The rationale for the U. This product is not intended to diagnose, treat, cure, or prevent any disease. Although many dietary ingredients have been introduced into dietary supplements since October and have not been submitted to the FDA for a safety review, nutritional supplementation writ large is generally safe. Perhaps more alarming is a report by the Centers for Disease Control suggesting 2,, emergency room visits were due to prescription drug-related events which dwarfs the emergency room visits due to dietary supplements adjusted from 23, visits after excluding cases of older adults choking on pills, allergic reactions, unsupervised children consuming too many vitamins, and persons consuming ingredients not defined by DSHEA as a dietary supplement [ 5 ].
Notwithstanding, there have been case reports of liver and kidney toxicity potentially caused by supplements containing herbal extracts [ 7 ] as well as overdoses associated with pure caffeine anhydrous ingestion [ 8 ]. Collectively, the aforementioned statistics and case reports demonstrate that while generally safe, as with food or prescription drug consumption, dietary supplement consumption can lead to adverse events in spite of DSHEA and current FDA regulations described below.
Recognizing that new and untested dietary supplement products may pose unknown health issues, DSHEA distinguishes between products containing dietary ingredients that were already on the market and products containing new dietary ingredients that were not marketed prior to the enactment of the law. The first criterion is silent as to how and by whom presence in the food supply as food articles without chemical alteration is to be established.
The second criterion—applicable only to new dietary ingredients that have not been present in the food supply—requires manufacturers and distributors of the product to take certain actions. The guidance prompted great controversy, and FDA agreed to issue a revised draft guidance to address some of the issues raised by industry. The purpose of the Draft Guidance was to help manufacturers and distributors decide whether to submit a premarket safety notification to FDA, help prepare NDI notifications in a manner that allows FDA to review and respond more efficiently and quickly, and to improve the quality of NDI notifications.
The Draft Guidance has been criticized by industry and trade associations for its lack of clarity and other problems. Self-Affirmed GRAS is when a company has a team of scientific experts evaluate the safety of their ingredient. There is no requirement that the safety dossier be submitted to FDA but is used by the company as an internal document that may be relied upon if the ingredient is challenged by the FDA.
In any event, the likelihood of another revised Draft Guidance from FDA becoming available in the future is high, and possibly more enforcement actions taken against companies that market an NDI without submitting a notification. In response to growing criticism of the dietary supplement industry, the th Congress passed the first mandatory Adverse Event Reporting AER legislation for the dietary supplement industry.
After much debate in Congress and input from the FDA, the American Medical Association AMA , many of the major supplement trade associations, and a host of others all agreed that the legislation was necessary and the final version was approved by all. The law strengthens the regulatory structure for dietary supplements and builds greater consumer confidence, as consumers have a right to expect that if they report a serious adverse event to a dietary supplement marketer the FDA will be advised about it. An adverse event is any health-related event associated with the use of a dietary supplement that is adverse.
A serious adverse event is an adverse event that A results in i death, ii a life-threatening experience, iii inpatient hospitalization, iv a persistent or significant disability or incapacity, or v a congenital anomaly or birth defect; or B requires, based on reasonable medical judgment, a medical or surgical intervention to prevent an outcome described under subparagraph A.
Once it is determined that a serious adverse event has occurred, the manufacturer, packer, or distributor responsible person of a dietary supplement whose name appears on the label of the supplement shall submit to the Secretary of Health and Human Services any report received of the serious adverse event accompanied by a copy of the label on or within the retail packaging of the dietary supplement.
The responsible person has 15 business days to submit the report to FDA after being notified of the serious adverse event. Following the initial report, the responsible person must submit follow-up reports of new medical information that they receive for one-year. The FDA has various options to protect consumers from unsafe supplements. The FDA also has the authority to protect consumers from dietary supplements that do not present an imminent hazard to the public but do present certain risks of illness or injury to consumers. The law prohibits introducing adulterated products into interstate commerce.
The standard does not require proof that consumers have actually been harmed or even that a product will harm anyone. It was under this provision that the FDA concluded that dietary supplements containing ephedra, androstenedione, and DMAA presented an unreasonable risk. Most recently, FDA imposed an importation ban on the botanical Mitragyna speciose, better known as Kratom.
In , FDA issued Import Alert 54—15, which allows for detention without physical examination of dietary supplements and bulk dietary ingredients that are, or contain, Kratom. Criminal penalties are present for a conviction of introducing adulterated supplement products into interstate commerce. While the harms associated with dietary supplements may pale in comparison to those linked to prescription drugs, recent pronouncements from the U. Department of Justice confirm that the supplement industry is being watched vigilantly to protect the health and safety of the American public.
However, it was not until that the cGMPs were finally approved, and not until that the cGMPs applied across the industry, to large and small companies alike. The adherence to cGMPs has helped protect against contamination issues and should serve to improve consumer confidence in dietary supplements.
The market improved as companies became compliant with cGMPs, as these regulations imposed more stringent requirements such as Vendor Certification, Document Control Procedures, and Identity Testing. These compliance criteria addressed the problems that had damaged the reputation of the industry with a focus on quality control, record keeping, and documentation.
However, it does appear that some within the industry continue to struggle with compliance. In Fiscal Year , it was reported that approximately Further, Undoubtedly, relying on certificates of analysis from the raw materials supplier without further testing, or failing to conduct identity testing of a finished product, can result in the creation of a product that contains something it should not contain such as synthetic chemicals or even pharmaceutical drugs.
All members of the industry need to ensure compliance with cGMPs. According to the Nutrition Labeling and Education Act NLEA , the FDA can review and approve health claims claims describing the relationship between a food substance and a reduced risk of a disease or health-related condition for dietary ingredients and foods. However, since the law was passed it has only approved a few claims. The delay in reviewing health claims of dietary supplement ingredients resulted in a lawsuit, Pearson v.
Shalala , filed in After years of litigation, in the U. Court of Appeals for the District of Columbia Circuit ruled that qualified health claims may be made about dietary supplements with approval by FDA, as long as the statements are truthful and based on adequate science. Supplement or food companies wishing to make health claims or qualified health claims about supplements can submit research evidence to the FDA for review.
The FTC also regulates the supplement industry. Further, before marketing products, they must have evidence that their supplements are generally safe to meet all the requirements of DSHEA and FDA regulations. This has increased job opportunities for sports nutrition specialists as well as enhanced external funding opportunities for research groups interested in exercise and nutrition research. While the push for more research is due in part to greater scrutiny from the FDA and FTC, it is also in response to an increasingly competitive marketplace where established safety and efficacy attracts more consumer loyalty and helps ensure a longer lifespan for the product in commerce.
Companies that adhere to these ethical standards tend to prosper while those that do not will typically struggle to comply with FDA and FTC guidelines resulting in a loss of consumer confidence and an early demise for the product.
A common question posed by athletes, parents, and professionals surrounding dietary supplements relates to how they are manufactured and perceived supplement quality. In several cases, established companies who develop dietary supplements have research teams who scour the medical and scientific literature looking for potentially effective nutrients. These research teams often attend scientific meetings and review the latest patents, research abstracts presented at scientific meetings, and research publications. Leading companies invest in basic research on nutrients before developing their supplement formulations and often consult with leading researchers to discuss ideas about dietary supplements and their potential for commercialization.
Other companies wait until research has been presented in patents, research abstracts, or publications before developing nutritional formulations featuring the nutrient. Upon identification of new nutrients or potential formulations, the next step is to contact raw ingredient suppliers to see if the nutrient is available, if it is affordable, how much of it can be sourced and what is the available purity.
Sometimes, companies develop and pursue patents involving new processing and purification processes because the nutrient has not yet been extracted in a pure form or is not available in large quantities. Reputable raw material manufacturers conduct extensive tests to examine purity of their raw ingredients. When working on a new ingredient, companies often conduct series of toxicity studies on the new nutrient once a purified source has been identified. The company would then compile a safety dossier and communicate it to the FDA as a New Dietary Ingredient submission, with the hopes of it being allowed for lawful sale.
When a powdered formulation is designed, the list of ingredients and raw materials are typically sent to a flavoring house and packaging company to identify the best way to flavor and package the supplement. In the nutrition industry, several main flavoring houses and packaging companies exist who make many dietary supplements for supplement companies.
Most reputable dietary supplement manufacturers submit their production facilities to inspection from the FDA and adhere to GMP, which represent industry standards for good manufacturing of dietary supplements. Some companies also submit their products for independent testing by third-party companies to certify that their products meet label claims and that the product is free of various banned ingredients. For example, the certification service offered by NSF International includes product testing, GMP inspections, ongoing monitoring and use of the NSF Mark indicating products comply with inspection standards, and screening for contaminants.
More recently, companies have subjected their products for testing by third party companies to inspect for banned or unwanted substances. These types of tests help ensure that the dietary supplement made available to athletes do not contained substances banned by the International Olympic Committee or other athletic governing bodies e. While third-party testing does not guarantee that a supplement is void of banned substances, the likelihood is reduced e. Moreover, consumers can request copies of results of these tests and each product that has gone through testing and earned certification can be researched online to help athletes, coaches and support staff understand which products should be considered.
In many situations, companies who are not willing to provide copies of test results or certificates of analysis should be viewed with caution, particularly for individuals whose eligibility to participate might be compromised if a tainted product is consumed. The ISSN recommends that potential consumers undertake a systematic process of evaluating the validity and scientific merit of claims made when assessing the ergogenic value of a dietary supplement [ 1 , 4 ]. This can be accomplished by examining the theoretical rationale behind the supplement and determining whether there is any well-controlled data showing the supplement is effective.
Supplements based on sound scientific rationale with direct, supportive research showing effectiveness may be worth trying or recommending. Sports nutrition specialists should be a resource to help their clients interpret the scientific and medical research that may impact their welfare and help them train more effectively. The following are recommended questions to ask when evaluating the potential ergogenic value of a supplement.
Most supplements that have been marketed to improve health or exercise performance are based on theoretical applications derived from basic science or clinical research studies. Based on these preliminary studies, a dietary approach or supplement is often marketed to people proclaiming the benefits observed in these basic research studies.
Although the theory may appear relevant, critical analysis of this process often reveals flaws in the scientific logic or that the claims made do not quite match up with the cited literature. By evaluating the literature one can discern whether or not a dietary approach or supplement has been based on sound scientific evidence. To do so, one is recommended to first read reviews about the training method, nutrient, or supplement from researchers who have been intimately involved in the available research and consult reliable references about nutritional and herbal supplements [ 1 , 9 ].
To aid in this endeavour, the ISSN has published position statement on topics related to creatine [ 10 ], protein [ 11 ], beta-alanine [ 12 ], nutrient timing [ 13 ], caffeine [ 14 ], HMB [ 15 ], meal frequency [ 16 ], energy drinks [ 17 ], and diets and body composition [ 18 ]. Each of these documents would be excellent resources for any of these topics.
In addition, other review articles and consensus statements have been published by other researchers and research groups that evaluate dietary supplements, offer recommendations on interpreting the literature, and discuss the available findings for several ingredients that are discussed in this document [ 19 — 21 ].
A quick look at these references will often help determine if the theoretical impetus for supplementing with an ingredient is plausible or not. Proponents of ergogenic aids often overstate claims made about training devices and dietary supplements while opponents of ergogenic aids and dietary supplements are often either unaware or are ignorant of research supporting their use.
Sports nutrition specialists have the responsibility to know the literature and search available databases to evaluate the level of merit surrounding a proposed ergogenic aid. Some athletic associations have banned the use of various nutritional supplements e. Obviously, if the supplement is banned, the sports nutrition specialist should discourage its use.
In addition, many supplements lack appropriate long-term safety data. People who consider taking nutritional supplements should be well aware of the potential side effects so they can make an informed decision whether to use a supplement. Additionally, they should consult with a knowledgeable physician to see if any underlying medical problems exist that may contraindicate its use.
When evaluating the safety of a supplement, it is suggested to determine if any side effects have been reported in the scientific or medical literature. In particular, we suggest determining how long a particular supplement has been studied, the dosages evaluated, and whether any side effects were observed. Unfortunately, many available supplements have not had basic safety studies completed that replicate the length of time and dosages being used. The next question to ask is whether any well-controlled data are available showing effectiveness of the proposed ergogenic aid in athletic populations or people regularly involved in exercise training.
The first place to look is the list of references cited in marketing material supporting their claims. Are the abstracts or articles cited just general references or specific studies that have evaluated the efficacy of the nutrients included in the formulation or of the actual supplement? From there, one can critically evaluate the cited abstracts and articles by asking a series of questions:.
For perspective, studies reporting improved performance in rats or an individual diagnosed with type 2 diabetes may be insightful, but research conducted on non-diabetic athletes is much more practical and relevant. Were the studies well controlled? For ergogenic aid research, the gold standard study design is a randomized, double-blind, placebo controlled clinical trial.
This means that neither the researcher nor the subject is aware which group received the supplement or the placebo during the study and that the subjects were randomly assigned into the placebo or supplement group. At times, supplement claims have been based on poorly designed studies i. Well-controlled clinical trials provide stronger evidence as to the potential ergogenic value and importantly how the findings can best be used. Do the studies report statistically significant results or are claims being made on non-significant means or trends?
Appropriate statistical analysis of research results allows for an unbiased interpretation of data. Although studies reporting statistical trends may be of interest and lead researchers to conduct additional research, studies reporting statistically significant results are obviously more convincing. With this said, it is important for people to understand that oftentimes the potential effect a dietary supplement or diet regimen may have above and beyond the effect seen from the exercise bout or an accepted dietary approach is quite small.
In addition, many studies examining a biochemical or molecular biology mechanism can require invasive sampling techniques or the study population being recruited is unique very highly trained resulting in a small number of study participants. When viewed together, the combination of these two considerations can result in statistical outcomes that do not reach statistical significance even though large mean changes were observed. In all such cases, additional research is warranted to further examine the potential ergogenic aid before conclusions can be made.
Do the results of the cited studies match the claims made about the supplement or do they accurately portray the response of the supplement against an appropriate placebo or control group? It is not unusual for marketing claims to greatly exaggerate the results found in the actual studies and do so by focusing upon just the outcomes within the supplement treatment group as opposed to how the supplement group changed in comparison to how a placebo group changed.
Similarly, it is not uncommon for ostensibly compelling results, that may indeed be statistically significant, to be amplified while other relevant findings of significant consumer interest are obscured or omitted e.
Reputable companies accurately and completely report results of studies so that consumers can make informed decisions about using a product. At times, claims are based on research that has either never been published or only published in an obscure journal. If you see only a few other journals this is a suggestion that the journal is not a reputable journal. Most journals list their impact factor on the journal home page. Historically, those articles that are read and cited the most are the most impactful scientifically.
Have the research findings been replicated? If so, have the results only been replicated at the same laboratory? The best way to know an ergogenic aid works is to see that results have been replicated in several studies preferably by several separate, distinct research groups. The most reliable ergogenic aids are those in which multiple studies, conducted at different labs, have reported similar results of safety and efficacy. Additionally, replication of results by different, unaffiliated labs with completely different authors also removes or reduces the potentially confounding element of publication bias publication of studies showing only positive results and conflicts of interest.
A notable number of studies on ergogenic aids are conducted in collaboration with one or more research scientists or co-authors that have a real or perceived economic interest in the outcome of the study. This could range from being a co-inventor on a patent application that is the subject of the ergogenic aid, being paid or receiving royalties from the creation of a dietary supplement formulation, providing consulting services for the company or having stock options or shares in a company that owns or markets the ergogenic aid described in the study.
An increasing number of journals require disclosures by all authors of scientific articles, and including such disclosures in published articles. This is driven by the aim of providing greater transparency and research integrity. It is important to emphasize that disclosure of a conflict of interest does not alone discredit or dilute the merits of a research study. The primary thrust behind public disclosures of potential conflicts of interest is first and foremost transparency to the reader and second to prevent a later revelation of some form of confounding interest that has the potential of discrediting the study in question, the findings of the study, the authors, and even the research center or institution where the study was conducted.
Dietary supplements may contain carbohydrate, protein, fat, minerals, vitamins, herbs, enzymes, metabolic intermediates i. Supplements can generally be classified as convenience supplements e. As discussed previously, evaluating the available scientific literature is an important step in determining the efficacy of any diet, diet program or dietary supplement. In considering this, nutritional supplements can be categorized in the following manner:. Strong Evidence to Support Efficacy and Apparently Safe: Supplements that have a sound theoretical rationale with the majority of available research in relevant populations using appropriate dosing regimens demonstrating both its efficacy and safety.
Limited or Mixed Evidence to Support Efficacy: Supplements within this category are characterized as having a sound scientific rationale for its use, but the available research has failed to produce consistent outcomes supporting its efficacy. Routinely, these supplements require more research to be completed before researchers can begin to understand their impact. Importantly, these supplements have no available evidence to suggest they lack safety or should be viewed as harmful.
Several factors are evaluated when beginning to counsel individuals who regularly complete exercise training. To accomplish this, one should make sure the athlete is eating an energy balanced, nutrient dense diet that meets their estimated daily energy needs and that they are training intelligently. Far too many athletes or coaches focus too heavily upon supplementation or applications of supplementation and neglect these key fundamental aspects. Following this, we suggest that they generally only recommend supplements in category I i.
If an athlete is interested in trying supplements in category II i. We believe this approach is scientifically substantiated and offers a balanced view as opposed to simply dismissing the use of all dietary supplements. A well-designed diet that meets energy intake needs and incorporates proper timing of nutrients is the foundation upon which a good training program can be developed [ 22 , 23 ].
Incorporating good dietary practices as part of a training program is one way to help optimize training adaptations and prevent overtraining. The following is an overview of energy intake recommendations and major nutrient needs for active individuals. The primary component to optimize training and performance through nutrition is to ensure the athlete is consuming enough calories to offset energy expenditure [ 22 — 26 ].
People who participate in a general fitness program e. However, athletes involved in moderate levels of intense training e. For elite athletes, energy expenditure during heavy training or competition will further exceed these levels [ 27 , 28 ]. Additionally, caloric needs for large athletes i. This point was clearly highlighted in a review by Burke who demonstrated that carbohydrate needs are largely unmet by high-level athletes [ 22 ]. Additionally it is difficult to consume enough food and maintain gastrointestinal comfort to train or race at peak levels [ 35 ].
Maintaining an energy deficient diet during training often leads to a number of physical i. It is still a question whether there may be specific individualized occasions when negative energy balance may enhance performance in the days prior to running performance [ 36 ]. Populations susceptible to negative energy balance include runners, cyclists, swimmers, triathletes, gymnasts, skaters, dancers, wrestlers, boxers, and athletes attempting to lose weight too quickly [ 37 ].
Additionally, female athletes are at particular risk of under fueling due to both competitive and aesthetic demands of their sport and their surrounding culture. Female athletes have been reported to have a high incidence of eating disorders [ 38 ]. This makes LEA a major nutritional concern for female athletes [ 39 ]. Consequently, it is important for the sports nutrition specialist working with athletes to assess athletes individually to ensure that athletes are well fed according to the goals of their sport and their health, and consume enough calories to offset the increased energy demands of training, and maintain body weight.
Further, travel and training schedules may limit food availability or the types of food athletes are accustomed to eating. This means that care should be taken to plan meal times in concert with training, as well as to make sure athletes have sufficient availability of nutrient dense foods throughout the day for snacking between meals e. Beyond optimal energy intake, consuming adequate amounts of carbohydrate, protein, and fat is important for athletes to optimize their training and performance. In particular and as it relates to exercise performance, the need for optimal carbohydrates before, during and after intense and high-volume bouts of training and competition is evident [ 41 ].
Excellent reviews [ 42 , 43 ] and original investigations [ 44 — 49 ] continue to highlight the known dependence on carbohydrates that exists for athletes competing to win various endurance and team sport activities. A complete discussion of the needs of carbohydrates and strategies to deliver optimal carbohydrate and replenish lost muscle and liver glycogen extend beyond the scope of this paper, but the reader is referred to several informative reviews on the topic [ 23 , 41 , 50 — 53 ].
As such, individuals engaged in a general fitness program and are not necessarily training to meet any type of performance goal can typically meet daily carbohydrate needs by consuming a normal diet i. However, athletes involved in moderate and high-volume training need greater amounts of carbohydrate and protein discussed later in their diet to meet macronutrient needs [ 50 ]. In terms of carbohydrate needs, athletes involved in moderate amounts of intense training e.
Research has also shown that athletes involved in high volume intense training e. Preferably, the majority of dietary carbohydrate should come from whole grains, vegetables, fruits, etc. When considering the carbohydrate needs throughout an exercise session, several key factors should be considered. Several reviews advocate the ingestion of 0. It is now well established that different types of carbohydrates can be oxidized at different rates in skeletal muscle due to the involvement of different transporter proteins that result in carbohydrate uptake [ 55 — 59 ].
Interestingly, combinations of glucose and sucrose or maltodextrin and fructose have been reported to promote greater exogenous rates of carbohydrate oxidation when compared to situations when single sources of carbohydrate are ingested [ 55 — 63 ]. These studies generally indicate a ratio of 1—1. In addition to oxidation rates and carbohydrate types, the fasting status and duration of the exercise bout also function as key variables for athletes and coaches to consider. When considering duration, associated reviews have documented that bouts of moderate to intense exercise need to reach exercise durations that extend well into 90th minute of exercise before carbohydrate is shown to consistently yield an ergogenic outcome [ 41 , 68 , 69 ].
Currently the mechanisms surrounding these findings are, respectively, thought to be replacement of depleted carbohydrate stores during longer duration of moderate intensity while benefits seen during shorter, more intense exercise bouts are thought to operate in a central fashion. Moreover, these reviews have also pointed to the impact of fasting status on documentation of ergogenic outcomes [ 41 , 68 , 69 ].
In this respect, when studies require study participants to commence exercise in a fasted state, ergogenic outcomes are more consistently reported, yet other authors have questioned the ecological validity of this approach for competing athletes [ 43 ]. As it stands, the need for optimal carbohydrates in the diet for those athletes seeking maximal physical performance is unquestioned. Daily consumption of appropriate amounts of carbohydrate is the first and most important step for any competing athlete.
Once exercise ceases, several dietary strategies can be considered to maximally replace lost muscle and liver glycogen, particularly if a limited window of recovery exists. In these situations, the first priority should lie with achieving aggressive intakes of carbohydrate while strategies such as ingesting protein with lower carbohydrate amounts, carbohydrate and caffeine co-ingestion or certain forms of carbohydrate may also help to facilitate rapid assimilation of lost glycogen. Initially, it was recommended that athletes do not need to ingest more than the RDA for protein i.
If an insufficient amount of protein is consumed, an athlete will develop and maintain a negative nitrogen balance, indicating protein catabolism and slow recovery. Over time, this may lead to muscle wasting, injuries, illness, and training intolerance [ 76 , 77 , 81 ]. For people involved in a general fitness program or simply interested in optimizing their health, recent research suggests protein needs may also be above the RDA. Phillips and colleagues [ 76 ], Witard et al. In this respect, Morton and investigators [ 83 ] performed a meta-review and meta-regression involving 49 studies and participants and concluded that a daily protein intake of 1.
Consequently, it is recommended that athletes involved in moderate amounts of intense training consume 1. Although smaller athletes typically can ingest this amount of protein, on a daily basis, in their normal diet, larger athletes often have difficulty consuming this much dietary protein. Additionally, a number of athletic populations are known to be susceptible to protein malnutrition e. Overall, it goes without saying that care should be taken to ensure that athletes consume a sufficient amount of quality protein in their diet to maintain nitrogen balance. Proteins differ based on their source, amino acid profile, and the methods of processing or isolating the protein undergoes [ 11 ].
These differences influence the availability of amino acids and peptides, which may possess biological activity e. For example, different types of proteins e. Therefore, care should be taken not only to make sure the athlete consumes enough protein in their diet but also that the protein is high quality. The best dietary sources of low fat, high quality protein are light skinless chicken, fish, egg whites, very lean cuts of beef and skim milk casein and whey while protein supplements routinely contain whey, casein, milk and egg protein.
In what is still an emerging area of research, various plant sources of protein have been examined for their ability to stimulate increases in muscle protein synthesis [ 77 , 97 ] and promote exercise training adaptations [ 98 ]. While amino acid absorption from plant proteins is generally slower, leucine from rice protein has been found to be absorbed even faster than from whey [ 99 ], while digestive enzymes [ ], probiotics [ ] and HMB [ ] can be used to overcome differences in protein quality.
Preliminary findings suggest that rice [ 98 ] and pea protein [ ] may be able to stimulate similar changes in fat-free mass and strength as whey protein, although the reader should understand that many other factors dose provided, training status of participants, duration of training and supplementation, etc. While many reasons and scenarios exist for why an athlete may choose to supplement their diet with protein powders or other forms of protein supplements, this practice is not considered to be an absolute requirement for increased performance and adaptations.
Due to nutritional, societal, emotional and psychological reasons, it is preferable for the majority of daily protein consumed by athletes to occur as part of a food or meal. However, we recognize and embrace the reality that situations commonly arise where efficiently delivering a high-quality source of protein takes precedence. Jager and colleagues [ 11 ] published an updated position statement of the International Society of Sports Nutrition that is summarized by the following points:. An acute exercise stimulus, particularly resistance exercise and protein ingestion both stimulate muscle protein synthesis MPS and are synergistic when protein consumption occurs before or after resistance exercise.
For building and maintaining muscle mass, an overall daily protein intake of 1. Higher protein intakes 2. Optimal doses for athletes to maximize MPS are mixed and are dependent upon age and recent resistance exercise stimuli. General recommendations are 0. Rapidly digested proteins that contain high proportions of EAAs and adequate leucine, are most effective in stimulating MPS.
Different types and quality of protein can affect amino acid bioavailability following protein supplementation; complete protein sources deliver all required EAAs. The dietary recommendations of fat intake for athletes are similar to or slightly greater than dietary recommendations made to non-athletes to promote health.
Maintenance of energy balance, replenishment of intramuscular triacylglycerol stores and adequate consumption of essential fatty acids are important for athletes, and all serve as reasons for an increased intake of dietary fat [ ]. For example, higher-fat diets appear to maintain circulating testosterone concentrations better than low-fat diets [ — ].
Additionally, higher fat intakes may provide valuable translational evidence to the documented testosterone suppression which can occur during volume-type overtraining [ ]. In situations where an athlete may be interested in reducing their body fat, dietary fat intakes ranging from 0. This recommendation stems largely from available evidence in weight loss studies involving non-athletic individuals that people who are most successful in losing weight and maintaining the weight loss are those who ingest reduced amounts of fat in their diet [ , ] although this is not always the case [ ].
Strategies to help athletes manage dietary fat intake include teaching them which foods contain various types of fat so that they can make better food choices and how to count fat grams [ 2 , 33 ]. For years, high-fat diets have been used by athletes with the majority of evidence showing no ergogenic benefit and consistent gastrointestinal challenges [ ]. In recent years, significant debate has swirled regarding the impact of increasing dietary fat. While intramuscular adaptations result that may theoretically impact performance [ , ], no consistent, favorable impact on performance has been documented [ , ].
A variant of high-fat diets, ketogenic diets, have increased in popularity. This diet prescription leads to a greater reliance on ketones as a fuel source. Currently, limited and mixed evidence remains regarding the overall efficacy of a ketogenic diet for athletes. In favor, Cox et al.
In light of the available evidence being limited and mixed, more human research needs to be completed before appropriate recommendations can be made towards the use of high fat diets for athletic performance. In addition to the general nutritional guidelines described above, research has also demonstrated that timing and composition of meals consumed may play a role in optimizing performance, training adaptations, and preventing overtraining [ 2 , 25 , 40 ].
This means that if an athlete trains in the afternoon, breakfast can be viewed to have great importance to top off muscle and liver glycogen levels. This also serves to increase availability of amino acids, decrease exercise-induced catabolism of protein, and minimize muscle damage [ — ]. Additionally, athletes who are going through periods of energy restriction to meet weight or aesthetic demands of sports should understand that protein intake, quality and timing as well as combination with carbohydrate is particularly important to maintain lean body mass, training effects, and performance [ 25 ].
Notably, this strategy becomes even more important if the athlete is under-fueled prior to the exercise task or is fasted vs. Following intense exercise, athletes should consume carbohydrate and protein e. This eating strategy has been shown to supersaturate carbohydrate stores prior to competition and improve endurance exercise capacity [ 2 , 40 ]. Thus, the type of meal, amount of carbohydrate consumed, and timing of eating are important factors to maximize glycogen storage and in maintaining carbohydrate availability during training while also potentially decreasing the incidence of overtraining.
The ISSN has adopted a position stand on nutrient timing in [ ] that has been subsequently revised [ 13 ] and can be summarized with the following points:. The importance of this strategy is increased when poor feeding or recovery strategies were employed prior to exercise commencement. Consequently, when carbohydrate delivery is inadequate, adding protein may help increase performance, mitigate muscle damage, promote euglycemia, and facilitate glycogen re-synthesis.
However, the size 0. Similar increases in MPS have been found when high-quality proteins are ingested immediately before exercise. Vitamins are essential organic compounds that serve to regulate metabolic and neurological processes, energy synthesis, and prevent destruction of cells.
Water-soluble vitamins consist of the entire complex of B-vitamins and vitamin C. Since these vitamins are water-soluble, excessive intake of these vitamins are eliminated in urine, with few exceptions e. Research has demonstrated that specific vitamins possess various health benefits e. Alternatively, if an athlete is deficient in a vitamin, supplementation or diet modifications to improve vitamin status can consistently improve health and performance [ ].
Furthermore, while optimal levels of vitamin D have been linked to improved muscle health [ ] and strength [ ] in general populations, research studies conducted in athletes generally fail to report on the ergogenic impact of vitamin D in athletes [ , ]. However, equivocal evidence from Wyon et al. The remaining vitamins reviewed appear to have little ergogenic value for athletes who consume a normal, nutrient dense diet. Finally, athletes may desire to consume a vitamin or mineral for various health non-performance related reasons including niacin to elevate high density lipoprotein HDL cholesterol levels and decrease risk of heart disease niacin , vitamin E for its antioxidant potential, vitamin D for its ability to preserve musculoskeletal function, or vitamin C to promote and maintain a healthy immune system.
Updated in Minerals are essential inorganic elements necessary for a host of metabolic processes. Minerals serve as structure for tissue, important components of enzymes and hormones, and regulators of metabolic and neural control. Notably, acute changes in sodium, potassium and magnesium throughout a continued bout of moderate to high intensity exercise are considerable.
In these situations, athletes must work to ingest foods and fluids to replace these losses, while physiological adaptations to sweat composition and fluid retention will also occur to promote a necessary balance. Like vitamins, when mineral status is inadequate, exercise capacity may be reduced and when minerals are supplemented in deficient athletes, exercise capacity has been shown to improve [ ].
However, scientific reports consistently fail to document a performance improvement due to mineral supplementation when vitamin and mineral status is adequate [ , , ]. For example, calcium supplementation in athletes susceptible to premature osteoporosis may help maintain bone mass [ ]. Increasing dietary availability of salt sodium chloride during the initial days of exercise training in the heat helps to maintain fluid balance and prevent dehydration. Finally, zinc supplementation during training can support changes in immune status in response to exercise training.
However, there is little evidence that boron, chromium, magnesium, or vanadium affect exercise capacity or training adaptations in healthy individuals eating a normal diet. The most important nutritional ergogenic aid for athletes is water and limiting dehydration during exercise is one of the most effective ways to maintain exercise capacity. Before starting exercise, it is highly recommended that individuals are adequately hydrated [ ]. When one considers that average sweat rates are reported to be 0. For this reason, it is critical that athletes adopt a mind set to prevent dehydration first by promoting optimal levels of pre-exercise hydration.
Throughout the day and without any consideration of when exercise is occurring, a key goal is for an athlete to drink enough fluids to maintain their body weight. Consequently, to maintain fluid balance and prevent dehydration, athletes need to plan on ingesting 0. Athletes should not depend on thirst to prompt them to drink because people do not typically get thirsty until they have lost a significant amount of fluid through sweat.
Additionally, athletes should weigh themselves prior to and following exercise training to monitor changes in fluid balance and then can work to replace their lost fluid [ , — ]. During and after exercise, athletes should consume three cups of water for every pound lost during exercise to promote adequate rehydration [ ]. A primary goal soon after exercise should be to completely replace lost fluid and electrolytes during a training session or competition. Additionally, sodium intake in the form of glucose-electrolyte solutions vs. Finally, inappropriate and excessive weight loss techniques e.
Sport nutritionists, dietitians, and athletic trainers can play an important role in educating athletes and coaches about proper hydration methods and supervising fluid intake during training and competition. Educating athletes and coaches about nutrition and how to structure their diet to optimize performance and recovery are key areas of involvement for sport dietitians and nutritionists. Currently, use of dietary supplements by athletes and athletic populations is widespread while their overall need and efficacy of certain ingredients remain up for debate.
Dietary supplements can play a meaningful role in helping athletes consume the proper amount of calories, macro- and micronutrients. Dietary supplements are not intended to replace a healthy diet. Supplementation with these nutrients in clinically validated amounts and at opportune times can help augment the normal diet to help optimize performance or support adaptations towards a training outcome.
Sport dietitians and nutritionists must be aware of the current data regarding nutrition, exercise, and performance and be honest about educating their clients about results of various studies whether pro or con. Currently, misleading information is available to the public and this position stand is intended to objectively rate many of the available ingredients. Additionally, athletes, coaches and trainers need to also heed the recommendations of scientists when recommendations are made according to the available literature and what will hopefully be free of bias.
We recognize that some ingredients may exhibit little potential to stimulate training adaptations or operate in an ergogenic fashion, but may favorably impact muscle recovery or exhibit health benefits that may be helpful for some populations. These outcomes are not the primary focus of this review and consequently, will not be discussed with the same level of detail. Consequently, meal replacements should be used in place of a meal during unique situations and are not intended to replace all meals.
Care should also be taken to make sure they do not contain any banned or prohibited nutrients. The following section provides an analysis of the scientific literature regarding nutritional supplements purported to promote skeletal muscle accretion in conjunction with the completion of a well-designed exercise-training program. An overview of each supplement and a general interpretation of how they should be categorized is provided throughout the text.
However, within each category all supplements are ordered alphabetically. For example, increases in body mass and lean mass are desired adaptations for many American football or rugby players and may improve performance in these activities. In contrast, decreases in body mass or fat mass may promote increases in performance such as cyclists and gymnasts whereby athletes such as wrestlers, weightlifters and boxers may need to rapidly reduce weight while maintaining muscle mass, strength and power. HMB is a metabolite of the amino acid leucine.
It is well-documented that supplementing with 1. The currently established minimal effective dose of HMB is 1. From a safety perspective, dosages of 1. The effects of HMB supplementation in trained athletes are less clear with selected studies reporting non-significant gains in muscle mass [ — ].
Before and after each supplementation period, body composition and performance parameters were assessed. When HMB was provided, fat mass was significantly reduced while changes in lean mass were not significant between groups. In this report, fat mass was found to be significantly reduced while fat-free mass was significantly increased. In conclusion, a growing body of literature continues to offer support that HMB supplementation at dosages of 1.
In our view, the most effective nutritional supplement available to athletes to increase high intensity exercise capacity and muscle mass during training is creatine monohydrate. The gains in muscle mass appear to be a result of an improved ability to perform high intensity exercise enabling an athlete to train harder and thereby promote greater training adaptations and muscle hypertrophy [ — ]. The only clinically significant side effect occasionally reported from creatine monohydrate supplementation has been the potential for weight gain [ , , , ].
The ISSN position stand on creatine monohydrate [ 10 ] summarizes their findings as this:. Creatine monohydrate is the most effective ergogenic nutritional supplement currently available to athletes in terms of increasing high-intensity exercise capacity and lean body mass during training. Creatine monohydrate supplementation is not only safe, but has been reported to have a number of therapeutic benefits in healthy and diseased populations ranging from infants to the elderly. If proper precautions and supervision are provided, creatine monohydrate supplementation in children and adolescent athletes is acceptable and may provide a nutritional alternative with a favorable safety profile to potentially dangerous anabolic androgenic drugs.
At present, creatine monohydrate is the most extensively studied and clinically effective form of creatine for use in nutritional supplements in terms of muscle uptake and ability to increase high-intensity exercise capacity. The addition of carbohydrate or carbohydrate and protein to a creatine supplement appears to increase muscular uptake of creatine, although the effect on performance measures may not be greater than using creatine monohydrate alone. Initially, ingesting smaller amounts of creatine monohydrate e. Clinical populations have been supplemented with high levels of creatine monohydrate 0.
Further research is warranted to examine the potential medical benefits of creatine monohydrate and precursors like guanidinoacetic acid on sport, health and medicine. Research examining the impact of the essential amino acids on stimulating muscle protein synthesis is an extremely popular area. Theoretically, this may enhance increases in fat-free mass, but to date limited evidence exists to demonstrate that supplementation with non-intact sources of EAAs e. Moreover, other research has indicated that changes in muscle protein synthesis may not correlate with phenotypic adaptations to exercise training [ ].
An abundance of evidence is available, however, to indicate that ingestion of high-quality protein sources can heighten adaptations to resistance training [ ]. While various methods of protein quality assessment exist, most of these approaches center upon the amount of EAAs that are found within the protein source, and in nearly all situations, the highest quality protein sources are those containing the highest amounts of EAAs. To this point, a number of published studies are available that state the EAAs operate as a prerequisite to stimulate peak rates of muscle protein synthesis [ — ].
To better understand the impact of ingesting free-form amino acids versus an intact protein source, Katsanos et al. Protein accrual was greater when the amino acid dose was provided in an intact source. While the EAAs are comprised of nine separate amino acids, some individual EAAs have received considerable attention for their potential role in impacting protein translation and muscle protein synthesis.
In this respect, the branched-chain amino acids have been highlighted for their predominant role in stimulating muscle protein synthesis [ , ]. Interestingly, Moberg and investigators [ ] had trained volunteers complete a standardized bout of resistance training in conjunction with ingestion of placebo, leucine, BCAA or EAA while measuring changes in post-exercise activation of p70s6k.
They concluded that EAA ingestion led to a nine-fold greater increase in p70s6k activation and that these results were primarily attributable to the BCAAs. Finally, a study by Jackman et al. While significant, this magnitude of change was notably less than the post-exercise MPS responses seen when doses of whey protein that delivered similar amounts of the BCAAs were consumed [ 88 , ].
These outcomes led the authors to conclude that the full complement of EAAs was advised to maximally stimulate increases in MPS. After stomach pangs have been sensed, too many hours have passed without feeding the body. Other hunger cues can include fatigue, poor concentration, headaches, irritability, shakiness, and sleep disturbances. These symptoms are usually felt before the stomach pangs and should be acted on immediately to prevent more intense hunger and additional energy loss.
Fatigue Physical or mental exhaustion from overexertion. Case Study Nadia, a year-old collegiate softball pitcher, presents to the sports dietitian with complaints of headaches and fatigue. She is confused about why she continues to get headaches, as she drinks plenty of water throughout the day and during practices.
Nadia practices twice a day: 60 to 90 minutes of conditioning in the morning and 2 to 3 hours of skills practice in the afternoon. Nadia was asked to keep a 1-week food and exercise log that also emphasized rating her hunger level throughout the day. On review, the sports dietitian noted that Nadia had a hard time judging her hunger level, causing her to skip meals and snacks. Nadia rarely feels hungry throughout the day, but she often gets a headache a few hours after her morning practice and when she is studying in the evening.
The sports dietitian reviewed some of the common signs of hunger with Nadia. Nadia was surprised that hunger cues also include fatigue, poor concentration, headaches, irritability, shakiness, and sleep disturbances—not just stomach pangs. Nadia recognized that she often experiences one or more of these symptoms throughout the day. After just one day of following the plan, Nadia reported that her headaches subsided and her concentration in the classroom and on the field had greatly improved. Carbohydrates The main source of energy for all body functions, particularly brain and muscle functions; necessary for the metabolism of other nutrients.
Protein Made up of amino acids that act as the building blocks for muscles, blood, skin, hair, nails, and the internal organs. Fat A wide group of compounds that may be either solid or liquid at room temperature. Complex carbohydrates A carbohydrate composed of two or more linked simple-sugar molecules. Lean proteins Protein sources that are low in saturated or trans fats, including beans, nuts, nut butters, eggs, chicken, turkey, fish, and soy.
Choose complex carbohydrates, lean proteins, unsaturated fats, and plenty of fruits and vegetables to ensure variety in the diet. Carbohydrates include fruits, vegetables, breads, rice, pasta, potatoes, cereal, oatmeal, pretzels, and crackers. Healthy fats include oils, nuts, seeds, fatty fish, avocado, and nut butters.
Athletes can easily use the figure as a visual guide for proper eating both at home and on the road. Quick Fact Add a variety of colors to your plate; eating an assortment of fruits and vegetables will provide nutrients and flavor to your meals. Why are carbohydrates important for exercise? Carbohydrates are the single most important source of energy for athletic performance. They are a rapid source of fuel to the working muscle and are burned efficiently with or without the presence of oxygen.
Carbohydrates are oxidized broken down three times faster than fat and are the predominant energy source for fueling both aerobic and anaerobic activity. Consuming low-carbohydrate diets is not recommended, as they cause a decrease in muscle glycogen stores. This glycogen decrease can lead to premature muscle fatigue during exercise and may result in the body using its muscle protein as a source of energy.
Athletes who Oxidized A chemical reaction with oxygen. Aerobic In the presence of air or oxygen. Anaerobic In the absence of air or oxygen. Glycogen The major carbohydrate stored in animal cells, mainly in the muscle cells and some in the liver. Glycogen is converted to glucose and released into circulation, as needed, by the body.
Nerve conduction The transmission of impulses throughout the nerves in the body. Quick Fact Very high-carbohydrate diets can raise blood triglyceride levels, leading to increased fat stores and weight gain. Carbohydrates are the key to muscle contraction, nerve conduction, and brain function. Carbohydrates are essential before, during, and after exercise in order for the athlete to attain optimal performance and recovery. The average athlete has the capacity to store approximately to grams of carbohydrate as glycogen in the body.
Glycogen is stored in the body at three sites: muscle cells, liver, and blood Figure 2. Muscle cells are the largest source, storing approximately to grams 1, to 1, kcal. The liver is the second largest storage site, containing approximately 75 to grams to kcal. Blood is the smallest site, circulating approximately 25 grams kcal. Training and carbohydrate loading positively influence the amount of muscle glycogen stored.
The glycogen that is used during exercise is specific to the muscle being used. Although there are to grams of total glycogen stored throughout the muscles, only a certain percentage can be used, depending on which muscles are activated. What are the differences between simple and complex carbohydrates? Carbohydrates are either simple or complex.
Simple carbohydrates raise blood sugar levels quickly. Examples include bananas, raisins, white breads, and energy gels. After simple carbohydrates have been digested, they enter the bloodstream as glucose to provide a rapid source of energy to the brain and exercising muscles. Conversely, complex carbohydrates raise blood sugar levels more slowly. Examples include whole-grain cereals, oatmeal, whole-grain breads, beans, and apples with Simple carbohydrates A form of carbohydrate that exists as a monosaccharide or disaccharide.
Complex carbohydrates a carbohydrate composed of two or more linked simple-sugar molecules. It is not digestible by humans. Although dietary fiber provides no energy for cellular activity, it does help maintain a healthy digestive system, lower blood cholesterol levels, and regulate blood glucose levels. Total daily energy expenditure Total amount of calories energy expended by the body over a hour period.
After complex carbohydrates have been digested, they will enter the bloodstream at a slower rate than simple carbohydrates because of their higher dietary fiber content. Complex carbohydrates provide a longterm source of energy to the exercising muscle and have a higher nutritional value than simple carbohydrates, providing certain vitamins and minerals.
What are the general carbohydrate recommendations for endurance athletes? Carbohydrate requirements for endurance athletes will depend on the intensity and duration of the exercise or sport, total daily energy expenditure, gender, and environmental conditions.
Recommended guidelines for carbohydrate intake range between 5 and 12 grams of carbohydrates per kilogram of body weight. Table 1 depicts daily carbohydrate needs for various endurance exercise durations. Total body glycogen content can last an endurance athlete approximately 90 to minutes of continuous endurance exercise. Athletes engaged in high-intensity, short-duration activities such as sprinting and strength training have a unique carbohydrate requirement.
Protein is a crucial nutrient that is required for growth and repair of muscle and other body tissues. Additionally, protein plays a large role in the formation of hormones, hemoglobin blood , enzymes, and antibodies. Proteins are comprised of amino acids, and unlike carbohydrates, they are not stored in the muscles cells as a source of energy.
Most athletes usually get this amount of protein from their daily food intake. Overconsumption of protein may lead to increased fat storage and dehydration, and long-term use may cause kidney damage. What are the general protein requirements for athletes? Protein requirements for athletes are variable and depend on the intensity and duration of the exercise or sport, total daily energy expenditure, and gender. Protein needs can be adequately met through diet as long as total energy intake is sufficient.
Boosting protein intake above the recommended amounts will not provide an additional benefit to the athlete because there is a limit to the rate at which lean muscle mass can accrue. The overconsumption of protein, in excess of 2 grams per kilogram of body weight per day, could potentially lead to acute as well as chronic kidney damage. Athletes with kidney disease should be aware of the dangers of consuming high-protein diets. Daily protein requirements for endurance and strength athletes are listed in Table 2. General Sports Nutrition 7.
What is the role of protein in the body? Hormone A complex chemical substance produced in one part or organ of the body that initiates or regulates the activity of an organ or group of cells in another part. Enzymes Proteins that accelerate chemical reactions. Antibodies Part of the immune system that helps to combat and neutralize foreign bodies such as viruses, bacteria, and parasites. Amino acids The basic structural building units of proteins. Total energy intake Total amount of calories energy needed by the body over a hour period.
What are the potential health consequences of consuming more than the recommended amount of protein in the diet? Athletes should be aware of the potential health consequences associated with consuming higher than recommended amounts of dietary protein. High dietary protein intake can lead to numerous health consequences Table 3. Table 3 Possible Health Consequences of the Overconsumption of Protein Metabolites A substance produced by the process of metabolism or vital for a certain metabolic process.
Satiety Being full or satisfied. Decalcification A loss of calcium from teeth and bones. What are the two principle types of fat? The two principle types of fat in the diet are saturated and unsaturated. Unsaturated fats are found in liquid oils olive oil, canola oil, and peanut oil , nuts, seeds, avocados, and fish. General Sports Nutrition Fat can be an important source of long-term energy during exercise. It protects and insulates body organs and is necessary for absorption of fat-soluble vitamins A, D, E, and K. The side effects of a low-fat diet include dry skin, brittle nails, hair loss, decreased protection of organs, and a fatsoluble vitamin deficiency that leads to poor physical and mental performance.
Fat-soluble vitamins A group of vitamins that do not dissolve easily in water and require dietary fat for intestinal absorption and transport into the bloodstream. The fatsoluble vitamins are A, D, E, and K. Saturated fat Fat that can cause an increase in cholesterol levels and that increases the risk for heart disease. Trans fat Considered to be an unhealthy source of fat that often leads to cardiovascular disease if ingested in high amounts. Unsaturated fat A heart-healthy fat that has the potential to lower cholesterol levels and reduce heart disease. Monounsaturated fat A type of fat that is shown to reduce the incidences of heart disease.
Bonking A condition in which an athlete experiences extreme fatigue and an inability to maintain the current level of activity. Should my nutritional strategies differ before competition versus practice? What should I eat if I have only less than 2 hours between games? The strategies that an athlete has developed for practice should remain consistent in the competitive arena. The athlete must remain well fueled with highcarbohydrate foods and fluids during competition to help prevent bonking, gastrointestinal upset, cramping, and excessive muscle tissue damage.
Refueling is important to restore severely depleted glycogen stores as quickly as possible in order to perform effectively during the next game. Case Study Natalina is a year-old varsity soccer midfielder. Her position requires a lot of endurance and sprinting during the minute game. In the championship tournament, she will play two games per day with less than 2 hours between each game. She must consume foods that taste good, provide the necessary energy to fuel her performance for the second match, and are quickly digestable so that they do not bother her stomach.
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Natalina should consume a snack that is high in carbohydrates and low in proteins and fats immediately after the first game. These foods will be digested and enter the circulation quickly, helping Natalina to recover some of her energy stores in time for the next game and thus maintain a higher level of performance. Sadly, these are not always conducive to optimal performance. Many do not think about what to consume; rather, they consume whatever is available to them at the time. As a coach, I know that my athletes cannot get stronger or faster without choosing the proper foods; therefore, I strongly encourage my athletes to consult with the sports dietitian to educate them in helping to make proper food choices at home and on the road that will enhance their performance and recovery.
General Sports Nutrition A word of caution: Natalina should avoid consuming solids foods within 30 minutes of her second game. This will allow enough time for proper digestion and help to prevent stomach upset. During the 30 minutes before the game, Natalina should consume approximately 8 to 16 ounces 1 to 2 cups of water or sports drinks to ensure adequate hydration.
These products vary in caloric content, taste, texture, size, and nutrient content. It is important for an athlete to experiment with various products during practice and not during competition. An athlete should not try new foods, energy bars, energy gels, or sports drinks for the first time before or during a major competition or event, as this may result in gastrointestinal problems, causing impaired athletic performance.
What are the common causes of gastrointestinal distress in athletes? Gastrointestinal distress Distress that occurs in the upper or lower gastrointestinal tracts that can negatively impact sports performance. Gastrointestinal distress is unfortunately common in many athletes. Symptoms in the upper and lower part of the gastrointestinal tract can negatively impact performance during exercise and may also be felt after exercise.
Sport: The type of activity or sport the athlete is training and competing in may affect gastrointestinal symptoms. Sports that involve jostling or up and down movements during activity tend to cause more gastrointestinal distress than those that are more stable. For instance, athletes who participate in running and triathlon events or teams sports such as soccer, basketball, or lacrosse may experience more gastrointestinal distress than athletes who participate in swimming, cycling, or water polo.
Intensity: Exercise intensity can influence gastrointestinal symptoms. The more intense the exercise such as sprinting , the slower are the digestion and absorption rate from the stomach, leading to potential gastrointestinal problems. Age: Experience can be a factor that influences gastrointestinal symptoms.
Younger athletes tend to consume foods that they enjoy without thinking about the consequences that these foods will have during exercise. Age may not always be a positive, however. As athletes age, gastrointestinal motility may slow, resulting in decreased rates of digestion, absorption, and excretion, leading to an increased incidence of gastrointestinal upset. Gender: Women more often complain of gastrointestinal distress since females have a slower gastricemptying rate than men influenced by estrogen. Menstrual cramping has also been associated with diarrhea.
Highly anxious athletes who consume foods or fluids before exercise are generally the most susceptible to gastrointestinal distress. These athletes may feel nauseated and vomit before an event and generally avoid pre-workout meals and snacks. Ironically, avoiding a pre-race or pre-game meal or snack can also cause gastrointestinal problems in addition to promoting early-onset fatigue.
Athletes should experiment with various types and amounts of foods and fluids to see what works best for them see Question There is a physiological limit to the amount of fluid that can be emptied from the stomach into the small intestine and eventually into the circulation. The amount of fluid tolerated in the stomach will depend on the dynamics of the sport and the individual athlete. Fiber intake: Diets that are too high or too low in fiber may delay or speed up gastric-emptying rates. Diets that are higher in fiber content will delay gastric emptying, whereas diets low in fiber can accelerate gastric emptying.
Athletes should keep fibrous foods to a minimum before exercise or competitions to prevent potential gastrointestinal problems. Athletes must educate themselves on the potential causes of gastrointestinal distress and must listen to their bodies. Athletes may want to experiment with various foods and fluids during practice to establish a plan that reduces gastrointestinal issues. Understand that not all General Sports Nutrition consuming sports food or fluids to ensure that they do not overconsume a particular nutrient.
Medications: Excessive use of over-the-counter nonsteroidal anti-inflammatory pain medications, such as ibuprofen, Aleve, and Motrin, may have side effects such as irritation of the stomach lining. This stomach irritation, if severe, may lead to ulcers or other serious complications. An athlete who is suffering from an acute or chronic injury should consult with a healthcare provider on the appropriate use of over-the-counter medications.
Supplements: Some supplements are known to react with the stomach, whereas others may contain certain products that the athlete may not be able to tolerate. For example, iron supplements may cause constipation and nausea if taken on an empty stomach. Athletes should consult with a registered dietitian regarding any questions or concerns that they may have about supplement use and implications. Timing of meals, snacks, and fluids: Consuming meals, snacks, or fluids too close to the start of exercise or consuming products that may not optimize gastric emptying can have negative outcomes for the athlete.
Registered dietitian An individual trained to provide food and nutrition information and who has successfully passed the national registration exam for registered dietitians. Gastrointestinal distress is likely the result of poor timing or inadequate knowledge or experience.
International society of sports nutrition position stand: nutrient timing
Why is sleep important, and how much do I need? Sleep is essential to life and is as vital to the body as food and oxygen. One of the most common concerns of athletes is sleep. How much should athletes get, and what happens when they are unable to fulfill their sleep requirement? Sleep requirements for maintaining optimal health as well as physical and mental performance is 8. An athlete who requires 8 hours of sleep per night and is only getting 7 hours will, by the end of the week, accrue 7 hours of sleep debt.
A sleep debt of this magnitude is equivalent to the loss of one full night of sleep. Some of the common reasons for sleep deprivation in athletes include stress, workload, training early in the morning or late at night, overtraining, or medical conditions, as well as alcohol and stimulant consumption. Sleep debt is cumulative and must be restored as soon as possible. If the debt is not repaid, it will roll over to the following week. Athletes will then find themselves experiencing excessive sleepiness during the day and will likely fall asleep at inappropriate times and places, such as behind the wheel of the car, at work, or in the classroom.
The first 48 hours of total sleep deprivation has been shown to have deleterious effects on mental capacity only. Physical effects will not manifest until 72 hours. After falling asleep, an individual will enter NREM sleep first where very little dreaming occurs. REM sleep, on the other hand, involves a substantial amount of dreaming and is essential to helping the individual recover mentally. During the REM cycle, the mind attempts to process and organize all of the information that it has encountered during the day.
The REM cycle is a very active portion of sleep, even though the individual is unable to move; this is analogous to an automobile with the accelerator pressed down and the brake on at the same time. Alcohol consumption and certain medications have been demonstrated to disrupt the REM cycle and should be avoided before bedtime. The following conditions are necessary to induce healthy sleep: Non-rapid eye movement NREM The first stage of sleep where very little dreaming occurs.
General Sports Nutrition The body will find a way to catch up, and the longer the sleep debt goes on, the harder it will be to stay awake and perform. Another consequence of sleep deprivation is overeating. Research has shown that those who do not get enough sleep or have a hard time staying asleep will crave higher calorie foods and tend to overeat the next day. Studies have also shown that individuals who suffer from chronic sleep deprivation experience higher incidences of heart disease, obesity, diabetes, and ulcers.
Rapid eye movement REM This second stage of sleep involves a substantial amount of dreaming and is essential to helping individuals recover mentally. During the rapid eye movement cycle, the mind attempts to process and organize all of the information that it has encountered during the day. Keep the room dark. The room should be quiet. Noise should be kept to a minimum; the use of earplugs or noise-canceling headphones can be beneficial in reducing ambient noise.
The room temperature should be cool. A cooler surrounding will assist the athlete in falling asleep. Warm or hot surroundings add to the discomfort and are likely to disrupt normal sleep schedules. The use of a fan or air conditioner to keep temperatures cool will help to avoid unnecessary disruptions in sleep. Individuals have found that using their own pillow when traveling is a great way of helping them fall asleep in unfamiliar surroundings. Some effective strategies that an athlete can employ to help to reduce the effects of fatigue caused by sleep deprivation include napping and the strategic use of caffeine.
Although sleep loss must be paid back, napping can be a very effective short-term strategy to help the athlete prolong focus and attention when sleep deprived. The recommended amount of nap time is between 30 and 60 minutes; however, if an athlete can get more than 60 minutes of needed sleep, it is highly recommended that he or she do so. A 30to minute nap can prolong mental performance for approximately 2 hours. If the athlete has an important mental task to perform immediately after napping, then the 30 to 60 minutes is advisable, as any longer napping can produce a sense of grogginess that may last for up to 20 minutes or more on waking.
Caffeine is a central-nervous stimulant and has the capacity to increase mental focus, reduce physical and mental fatigue, and improve reaction time. Athletes should try to get a minimum of 8 hours of sleep per night to ensure optimal recovery and performance. If 8 hours is difficult to get at one time, an athlete should try to squeeze in naps throughout the day to help him or her catch up.
Insufficient sleep can cause lapses in attention that can lead to injuries. Getting the required amount of sleep each night will help the athlete avoid making basic mistakes. Anathea C. The correct use of caffeine has also been demonstrated to improve athletic performance. After 24 hours of continuous sleep deprivation, caffeine consumed at the right time in the right amounts has been scientifically proven to prolong mental performance for approximately 3 additional hours see Question Caffeine should not be consumed within 5 hours before bedtime, as it can interfere with sleep.
As a general-surgery resident, I had become detrained after many sleepless nights on call. In order to get ready for Ironman, I had to make up ground very quickly in a very short window of time during a research fellowship. In order to maximize my time and effort, I turned to experts in the field of sports nutrition and exercise science. With a professional and individualized nutrition and exercise program, I found that my body composition improved and my sleep patterns became more regulated, and I saw significant performance improvements in all of my sports.
I improved 83 minutes overall in my second Ironman race and gained an edge in every stage of the race. What are the basic principles of exercise that are needed to optimize training and performance? Why should athletes warm up before and cool down after exercise? This section offers athletes specific guidelines and tools to measure performance and to implement effective exercise concepts to prevent the common pitfalls that athletes regularly encounter.
What are the health benefits of regular exercise? Health is defined as freedom from disease. Numerous people are unaware that they are afflicted with risk factors that can lead to chronic illnesses such as heart disease, diabetes, stroke, and certain cancers. Many risk factors often have no physical symptoms silent , and thus, they are not felt by an individual. The most significant physiological risk factors for heart disease include high blood pressure hypertension , elevated blood lipids cholesterol and triglycerides , and high blood sugar hyperglycemia.
Additional risk factors include smoking, obesity, and a lack of physical activity. Quick Fact One of every four Americans has high blood pressure. Uncontrollable risk factors such as genetics, age, gender, and ethnicity play a significant part in the development of disease, but chronic illnesses such as heart disease and diabetes are commonly a result of individual lifestyle poor diet, smoking, a lack of exercise, etc. Contemporary medicine has made great strides in treating and controlling many of the chronic diseases plaguing modern society; however, this intervention comes with a hefty price tag to both the individual and the economy.
Heart disease is still the number-one killer of both men and women in Western society. Quick Fact , Americans die from heart disease every year. Cardiorespiratory exercise done three or more times per week for 30 to 60 minutes at a moderate intensity has been proven to lower the risk of heart disease. Greater benefits can be experienced with a higher frequency and duration, meaning more than three times per week and longer than 30 minutes.
The health benefits of regular exercise include reduced total blood lipids and blood pressure, improved lipid profiles, weight management, and a strong heart and circulatory system. Reduced blood lipid profiles: Studies have shown that regular exercise cardiorespiratory and resistance training can have a significant positive effect on blood lipid profiles. Additionally, the total cholesterol to highdensity lipoprotein ratio improves.
Low-density lipoprotein has been implicated in the development of arterial plaque, whereas high-density lipoprotein is known to reduce and potentially remove arterial plaque. Endurance exercise has a higher positive impact on blood lipid profiles than resistance exercise. Blood lipid profile A blood test that determines the amount of fat in the form of cholesterol and triglyceride in the circulation.
Plaque A build-up of lipids fats in the arteries of the heart that reduces blood flow. Diastole A resting phase of the heart where blood refills the chambers of the heart. Vascular resistance The resistance to blood flow that must be overcome to push blood through the circulatory system. Metabolize The breaking down of carbohydrates, proteins, and fats into smaller units; reorganizing those units as tissue building blocks or as energy sources; and eliminating waste products of the processes.
Insulin A naturally occurring hormone secreted by the cells of the pancreas in response to increased levels of glucose in the blood. The hormone acts to regulate the metabolism of glucose, fats, and proteins. Reduced blood pressure: Regular exercise has been shown to reduce blood pressure in hypertensive individuals. The effect is more pronounced in those who have moderate hypertension compared with individuals with severe hypertension. Average blood pressure decreases of 5 mm Hg systole and 7 mm Hg diastole have been confirmed in persons suffering from mild hypertension.
Although the physiological basis for the decrease in blood pressure resulting from endurance exercise is still unknown, it is theorized that endurance exercise may help to reduce vascular resistance. Active and fit individuals have been shown to be less susceptible to developing hypertension. Weight management: Exercise promotes weight loss and helps to maintain lean body mass.
Regular exercise aerobic and anaerobic in conjunction with a moderate reduction in calorie intake is an effective method for losing and maintaining weight. Exercise can help to metabolize glucose more efficiently from the circulation by increasing insulin sensitivity in the cells. This improved sensitivity helps to remove excess blood glucose for entry into the cells where it is stored as glycogen or immediately oxidized for energy.
Evidence exists that demonstrates the effects of exercise on stress reduction and smoking cessation. Strong heart and circulatory system: Chronic aerobic exercise has distinct anatomical and physiological effects on the human heart. Some of the more favorable changes from exercise include larger coronary arteries for better circulation, greater pumping capacity because of increased contractility, and a larger left ventricle for ejecting more blood per beat throughout the body.
All of these positive changes to the heart make it stronger, more efficient, and less susceptible to a heart attack. Exercise has been shown through research to reduce total blood lipids and blood pressure, improve lipid profiles, control weight, and strengthen the heart and circulatory system.
General Exercise Concepts Even though exercise is not the universal panacea to all diseases, it can have a profound effect on reducing or eliminating some of the more insidious risk factors associated with certain chronic illnesses. Anyone considering beginning an exercise program should make sure that he or she has first been given the green light by his or her physician. Consulting with a qualified and experienced exercise physiologist and registered dietitian is advisable to ensure that the program is scientifically based and safe. Athletes who are serious about their training and competition must ensure that they are optimally prepared by using the most current scientific methods that will allow for maximal adaptations and performance while reducing susceptibility to overtraining and injury.
In order for athletes to train and compete at the highest possible level, they must pay careful attention to scientifically sound and effective exercise strategies and principles. A well-designed exercise program, aerobic or anaerobic, should incorporate four general training principles: 1 specificity, 2 progression, 3 variation, and 4 overload. Specificity is a training principle that necessitates an athlete to train specifically for the sport or activity. The training program incorporates the physiological requirements for the activity, including the musculoskeletal, Specificity A training principle that necessitates an athlete to specifically train for the sport or activity.
If an athlete fails to integrate specificity into his or her training, he or she will most likely compromise his or her performance. For example, a high jumper would be best served by incorporating sport-specific movements, such as jump squats, plyometric drills, or power cleans, into his or her training program. These specific movements would prepare the jumper more effectively for competition than non—sport-specific movements.
Examples of non—sport-specific movements for this athlete include endurance running, leg extensions, or bench press; these movements have little transferability to the actual activity. An athlete should be monitored carefully during his or her prescribed workouts to determine when training loads need to be increased or decreased. For example, a discus thrower would have a detailed strength training program designed for an entire training year.
The program would be broken into specific cycles see Question 21 that would incorporate gradual increases in workload throughout the season. If an athlete decided to leap ahead of the program, breaking the designed progression, in all likelihood, the athlete would find himself or herself peaking prematurely and missing the opportunity to compete at his or her best. Variation Comes from changing workloads, exercises, or both.
Variation comes from changing workloads, exercises, or both. Varying the workloads weight lifted, sets, or repetitions is intended to prevent overtraining. Regular fluctuations must be built into the program to include changes in the volume and intensity of the training. Some days would incorporate strength, some strength endurance, and others power to allow for adequate recovery and maximal adaptation.
Changing exercises frequently can help to reduce boredom, improve fitness and performance, and stimulate renewed physiological adaptations through a multitude of diverse ranges of motion and planes of movement. After an athlete has adapted to a particular training load, that training load must be increased to create a stronger stimulus and further adaptation. If an athlete is not provided with a significant enough overload, further improvements in the physiological systems of the body will cease, and the athlete will plateau in his or her performance.
The training load is usually increased by a definite percentage each week to allow for proper adaptation. Overload A method of training that requires the physiological systems of the body to be increasingly stressed to ensure continued improvement. Frequency is defined as the number of training sessions per week. To maximize performance in longdistance running, an athlete would need to train between three and five times per week.
For a strength athlete, training can range between two and five sessions per week, depending on the sport. The training cycle usually determines the frequency of training and should be carefully manipulated to allow for maximal recovery, adaptation, and continued improvement. Frequency The number of training sessions per week. Training intensity The amount of effort low, moderate, high required to perform a specific exercise. Intensity How hard an athlete works during training and competition.
Training volume The total amount of work done during a training period. Athletes in the preseason phase of training getting ready to compete will spend less time exercising during each session because training intensity will be very high. Conversely, the off-season phase will generally involve longer training sessions with low to very low intensity. Intensity is probably the single most important variable, as it provides the required stimulus overload necessary for increasing performance. Intensity can come in the form of increasing the resistance lifted, working at a higher heart rate, or reducing the recovery time between sets of an exercise.
Athletes engaged in strength training programs usually determine intensity based on the repetition maximum. During the latter stages of the season, a runner may alternate days of low-, moderate-, and high-intensity training to ensure maximum recovery and performance. The basic principles of exercise were designed to help athletes improve performance, reduce injuries, and avoid overtraining. Warming up before exercise and cooling down after exercise are imperative to an athlete, helping to reduce injury, enhance performance, and promote recovery.
Many athletes overlook these stages of exercise, as they do not feel that they have the time or even understand the benefits of warming up or cooling down. To profit from a thorough warm-up and cool-down, an athlete must spend at least 10 minutes before workout and 5 minutes after workout stretching the major muscle groups and joints of the body. General Exercise Concepts There are two methods of warming up: dynamic and specific. A dynamic warm-up should consist of ten minutes of light exercise that involves the entire body, using both major and minor muscle groups. The warm-up should commence with five minutes of light jogging, stationary cycling, or jumping jacks, followed by dynamic muscle movements.
These movements can include walking lunges, backward running, lateral shuffling, one- and two-legged hops, and walking with alternating toe touches. The purpose behind the dynamic warm-up is to increase heart rate and blood flow to the working muscles and joints, raise muscle temperature, improve muscle elasticity and plasticity, and increase respiratory rate and change joint fluid viscosity.
A specific warm-up should consist of five minutes or more of sport-specific movements and stretches that simulate muscle and joint actions of the sport. For example, a basketball or volleyball player would spend time on his or her shoulder and hip muscles and joints by doing light jumping, spiking, and layup and shooting drills, and a baseball player would concentrate on specific throwing and upper-torso rotational movements.
The purpose behind a specific warm-up is to increase functional capacity, improving sport-specific performance. An athlete, whatever the sport, needs to take the time to work on sport-specific warm-ups to ensure maximal efficiency and injury reduction. After an intense training session or competition, an athlete must take five minutes to cool-down properly. Venous return The transportation of blood from the cells through the veins back to the heart. Syncope A sudden drop in blood pressure that causes dizziness and possible fainting.
The cool-down phase should involve a gradual reduction in the intensity of exercise, followed by stretching flexibility exercises see Question For example, at the end of a workout, a runner should reduce his or her running intensity to a light jog and then to a walk to prevent blood from pooling in his or her lower extremities.
Light jogging and walking after exercise aid in venous return. Venous return promotes blood flow back to the heart and lungs because of the muscles contracting against the veins. This venous return helps the athlete to recover faster and reduces the potential for syncope decreased blood flow to the brain , which can cause dizziness or fainting. Athletes of all ages and abilities should take the time to learn and apply warm-ups and cool-downs to their training programs.
Dynamic warm-up 10 minutes 1. Light jogging— meters 2. Light jogging with giant forward arm circle— meters 3. Light jogging with giant backward arm circles— meters 4. Side shuffle with lateral arm raises— meters 5. Carioca— meters B. Sport-specific warm-up 5 to 8 minutes 1. Walking lunges with alternating upperbody twists can use 2- to 4-pound medicine ball —1 for 50 yards see a and b a General Exercise Concepts the athlete recover faster and prevent the possibility of lightheadedness and fainting. Athletes need to ensure that the warm-up is not too intense, as it may interfere with their performance by causing premature fatigue.
During the cool-down phase, an athlete should bring his or her heart rate down to less than beats per minute to ensure proper recovery. In-place two-legged hops—1 for 30 seconds see c, d, and e d jump c start e finish 3. Light medicine ball 2 pound throws with partner see g and h or wall see i and j —1 for 30 seconds each arm i preparing to throw h throwing General Exercise Concepts g preparing to throw j throwing C. Cool-down 5 to 8 minutes 1. Very light walking or jogging—2 to 3 minutes 2. Shoulder stretches—3 for 20 to 30 seconds each see l l 4. Groin stretches—3 for 20 to 30 seconds each see m m 5.
How can I improve my flexibility? Flexibility is influenced by factors such as age, gender, activity level, and joint and tissue structure. As athletes age, the joints and surrounding tissue structures become more rigid and lose much of their elasticity, causing a decrease in range of motion.
Professor Fang Dongmei
This decreased flexibility is generally the result of fibrosis, a condition in which fibrous connective tissue replaces muscle fibers. Females tend to have more flexibility than males because of possible structural and anatomical differences and hormonal influences. Less active individuals are inclined to have a lower level of flexibility than more active individuals. Additionally, there are inherent joint and tissue structure differences joint capsules, tendons, ligaments, and skin between individuals that result in varying levels of flexibility.
Certain individuals have higher elasticity and plasticity components to their connective tissue, making them more flexible. Flexibility The range of motion about a joint. General Exercise Concepts Flexibility is the range of motion about a joint. It is an important component of all sports; thus, athletes should work on their flexibility year round before, during, and after the season. Athletes can improve their flexibility by incorporating three to four stretching sessions per week into their training schedule.
Conversely, flexibility can deteriorate with periods of inactivity, leading to an increase in susceptibility to serious injury. Fibrosis A condition in which fibrous connective tissue replaces muscle fibers. Flexibility can be attained during the warm-up and cool-down parts of a workout.
After the dynamic warm-up, when muscle temperature is higher, an athlete should spend at least 5 minutes working on his or her flexibility see Question Stretching before exercise can help to reduce injuries and increase performance through enhanced elasticity of muscles, tendons, and joint range of motion and functional ability. The cool-down phase is considered to be the optimal time to maximize flexibility. Active stretch When an athlete applies the force for the stretch. Passive stretch Requires the use of a device or person to apply the force for the stretch.
There are two recommended stretching techniques that improve flexibility: active stretching and passive stretching. An active stretch occurs when an athlete applies the force for the stretch. For example, the seated hamstring and lower back stretch requires the athlete to lean his or her upper torso to his or her lower torso and hold for a period of time. The passive stretch requires the assistance of a device or person to apply the force for the stretch.
Stretching can be subdivided into four basic stretch techniques: static, dynamic, ballistic, and proprioceptive neuromuscular facilitation. Static stretching Referred to as the stretch-hold technique. It begins by moving the joint and muscle through a range of motion until the stretch sensation is felt in the belly of the muscle. Dynamic stretching A method of stretching using sportsspecific movements to increase flexibility. Static stretching is often referred to as the stretch— hold technique.
The athlete begins the stretch by moving the joint and muscle through a range of motion until the stretch sensation is felt in the belly of the muscle. The stretch is then held for 20 to 30 seconds followed by a relaxation period of a few seconds. The stretch is repeated for two more repetitions trying to increase the range of motion each time using the same technique. The athlete should avoid stretching the muscle too intensely, as this could lead to injury. Static stretching is a very effective method for increasing flexibility and is generally considered to be safe.
Dynamic stretching is a method of stretching using sport-specific movements to increase flexibility. General Exercise Concepts This type of stretching helps to prepare an athlete for the movement patterns of his or her sport by stretching the involved muscles, tendons, and joints. Ballistic stretching is often referred to as the bounce technique. The movement is rapid with no hold bouncing at the end of the stretch. The muscle is stretched quickly, returned to its original position rapidly, and then stretched again.
Ballistic stretching has the potential to cause serious injury and should be avoided. During ballistic stretching, the muscle is never allowed to relax, which creates a stretch reflex in the muscle, causing it to tighten; this is counterproductive to the purpose of stretching. An example of a ballistic stretch is the standing toe touch. The athlete stands with his or her legs slightly apart and tries to touch his or her toes by bouncing up and down in rapid succession for a period of time.
If an athlete has a pre-existing back or hamstring injury, the potential for further injury using this stretch is high. Proprioceptive neuromuscular facilitation is often referred to as the stretch—hold—contract technique. Performance of this method of stretching usually requires a partner with a certain level of expertise. The proprioceptive neuromuscular facilitation method has been demonstrated to be a superior technique for developing flexibility, as it prolongs muscle relaxation after each stretch.
There are three different types of proprioceptive neuromuscular facilitation stretching; the most commonly used Proprioceptive neuromuscular facilitation Often referred to as the stretch—hold— contract technique. This method of stretching usually requires a partner with a certain level of expertise to perform. Flexibility can be acquired rapidly and has the potential to increase performance and reduce injury.
An example of the hold—relax—contract technique for a hamstring stretch requires the athlete to lie flat on his or her back. The athlete is required to keep the leg straight and the knee locked during the entire stretch. The isometric contraction on the leg is held for 6 seconds and then allowed to relax for a few seconds. The partner then applies a second passive stretch greater than the initial stretch and should be held for a period of 30 seconds.
This stretching technique can be applied to most joints of the body and is a very effective method for improving flexibility. Long periods of inactivity can decrease flexibility quickly and should be avoided. What is the difference between slow- and fast-twitch muscle fibers, and what role do they play during exercise? Human skeletal muscle is comprised of two different types of muscle fiber, slow twitch type 1 and fast twitch type 2 , in approximately equal amounts.
Fast-twitch fibers, on the other hand, are whitish in color, contract three to four times faster than slowtwitch fibers, have a low endurance capacity, and are considerably larger than slow-twitch fibers. Type 2 muscle fibers generate most of their ATP energy anaerobically without oxygen from carbohydrates glycolysis. Fast-twitch muscle fibers are recruited during high-intensity exercise such as sprinting and weight training. There are, however, distinct physiological differences between the type 2a and type 2b fast-twitch muscle fibers.
Myoglobin Found mainly in muscle tissue; serves as a storage site for oxygen. Mitochondria Powerhouses of the cell that burn carbohydrates, fats, and proteins for energy. General Exercise Concepts Slow-twitch muscle fibers have a reddish appearance because of their high myoglobin content and have a relatively slow contractile force. They have a high mitochondria content and are surrounded by numerous blood vessels capillaries that bring oxygen and nutrient-rich blood into the muscle.
Type 1 muscle fibers produce energy aerobically in the presence of oxygen and are very efficient at producing ATP energy needed for the contraction and relaxation of muscle from the oxidation of fats and carbohydrates; thus, they are recruited quickly, are remarkably fatigue resistant, and are used exclusively during endurance events such as marathon running and long-distance cycling. Glycolysis Breakdown of glucose into energy. Type 2a muscle fibers perform similarly to both fastand slow-twitch fibers; they have a relatively higher blood flow capacity, a higher capillary density, and a higher mitochondrial content than type 2b fibers, and they are relatively fatigue resistant.
Type 2a muscle fibers have some capacity for oxidative metabolism utilization of fats and carbohydrates for energy. Type 2b fibers have a very low blood supply, a low mitochondrial content, and a low capillary density, and they fatigue rapidly during exercise. Type 2b fibers are recruited during very intense exercise, such as a meter sprint or a meter sprint swim, and produce energy exclusively through anaerobic metabolism of carbohydrates.
The amount of force generated by type 2b muscle fibers is considerably greater than by type 2a, and in essence, a type 2b muscle fiber is a power fiber. During exhaustive exercise, such as marathon running, the body preferentially recruits slow-twitch muscle fibers first. At some undetermined point, slow-twitch fibers begin to fatigue from glycogen depletion.
The reduction in glycogen content eventually forces the body to transition to the fast-twitch type 2a fibers to maintain performance. When type 2a fibers exhaust their energy stores, the body finally activates the type 2b fibers to keep the muscles fueled. The ratio of fast-twitch to slow-twitch fibers appears to be genetically determined at a very young age, possibly the first few years of life.
Fiber distribution is inherited and cannot be significantly altered through training. Studies completed on identical twins clearly demonstrate inheritance as a major factor in determining fiber type and distribution; results prove that their fiber types are almost indistinguishable. Regular strength training has been shown to shift a small percentage of type 2a muscle fibers to type 2b. In addition, as an athlete ages, there appears to be an appreciable change in muscle fiber distribution, with a shift from fast-twitch to slowtwitch fibers.
The relative percentage and distribution of type 1 and type 2 muscle fibers usually steer an athlete into a particular sport or activity. Athletes who are endowed with a higher percentage of slow-twitch fiber are more likely to gravitate to endurance-type activities, such as marathon running. Conversely, athletes endowed with a higher percentage of fast-twitch fibers are more inclined to be better at strength or power sports, such as sprinting.
Athletes with almost equal ratios of type 1 and 2 fibers tend to be better at moderate- to high-intensity activities, such as the mile run. Most athletes discover what they are better suited to by experimenting with different activities at a young age. What is periodization? Why is it important? For decades, athletes prepared for competition by using a trial and error approach to their training. Training was rarely scientifically based, and athletes usually experimented with a variety of approaches hoping to discover the one that was most effective.
If a particular method failed to produce the desired results, athletes typically moved on to a different program. The ultimate cost of using an ad hoc approach to training frequently resulted in the athlete failing to reach his or her optimal athletic potential. Athletes often fell into the trap of training too hard too often and for too long, leading to unnecessary injuries and overtraining.
As a response to this hit-or-miss approach to training, Eastern European Bloc countries began developing and using a more scientific approach to athlete preparation. The scientific method of establishing a relationship between training intensity and volume over time is referred to as periodization. This method of training is very successful at preparing and peaking athletes for competition and has become the standardized training method for athletes throughout the world.
Periodization cycling is a system of training that allows individual variations in program volume and intensity over a specific period of time. The relationship between intensity and volume is typically an inverse one—in other words, as intensity increases, volume decreases and vice versa Figure 3.
The period covers an entire training Volume The amount of work done during an exercise bout. Periodization A method of training that varies the volume and intensity of training over a period of time to prevent overtraining. The classic periodization model Figure 4 is broken into three phases: macrocycle, mesocycle, and microcycle. The first phase, macrocycle, is the longest phase and is usually a year long. This cycle spans the four seasonal periods of off-season, postseason, pre-season, and in-season.