The use of dietary supplements is widespread among athletes in all sports and at all levels of competition, as it is in the general population. For the athlete training at the limits of what is sustainable, or for those seeking a shortcut to achieving their aims, supplements offer the prospect of bridging the gap between success and failure. Surveys show, however, that this is often not an informed choice and that the knowledge level among consumers is often low and that they are often influenced in their decisions by individuals with an equally inadequate understanding of the issues at stake. Supplement use may do more harm than good, unless it is based on a sound analysis of the evidence. Where a deficiency of an essential nutrient has been established by appropriate investigations, supplementation can provide a rapid and effective correction of the problem. Supplements can also provide a convenient and time-efficient solution to achieving the necessary intake of key nutrients such as protein and carbohydrate. Athletes contemplating the use of supplements should consider the potential for both positive and negative outcomes. Some ergogenic supplements may be of benefit to some athletes in some specific contexts, but many are less effective than is claimed. Some may be harmful to health of performance and some may contain agents prohibited by anti-doping regulations. Athletes should make informed choices that maximize the benefits while minimizing the risks.
Ronald J. Maughan, Susan M. Shirreffs and Alan Vernec
Louise M. Burke and Peter Peeling
Many expert sporting bodies now support a pragmatic acceptance of the use of performance supplements which have passed a risk:benefit analysis of being safe, effective, and permitted for use, while also being appropriate to the athlete’s age and maturation in their sport. However, gaining evidence of the performance benefits of these supplements is a process challenged by the scarcity of research in relation to the number of available products, and the limitations of the poor quality of some studies. While meta-analyses and systematic reviews can help to provide information about the general use of performance supplements, the controlled scientific trial provides the basis on which these reviews are undertaken, as well as an opportunity to address more specific questions about supplement applications. Guidelines for the design of studies include the choice of well-trained athletes who are familiarized with performance tasks that have been chosen on their basis of their known reliability and validity. Supplement protocols should be chosen to maximize the likely benefits, and researchers should also make efforts to control confounding variables, while keeping conditions similar to real-life practices. Performance changes should be interpreted in light of what is meaningful to the outcomes of sporting competition. Issues that have been poorly addressed to date include the use of several supplements in combination and the use of the same supplement over successive events, both within a single, and across multiple competition days. Strategies to isolate and explain the variability of benefits to individuals are also a topic for future investigation.
Romain Meeusen and Lieselot Decroix
Cognitive function plays an important role in athletic performance, and it seems that brain functioning can be influenced by nutrition and dietary components. Thus, the central nervous system might be manipulated through changes in diet or supplementation with specific nutrients including branched-chain amino acids, tyrosine, carbohydrates, and caffeine. Despite some evidence that branched-chained amino acids can influence ratings of perceived exertion and mental performance, several well-controlled studies have failed to demonstrate a positive effect on exercise performance. Evidence of an ergogenic benefit of tyrosine supplementation during prolonged exercise is limited. There is evidence that mild dehydration can impair cognitive performance and mood. The beneficial effect of carbohydrate supplementation during prolonged exercise could relate to increased substrate delivery for the brain, with numerous studies indicating that hypoglycemia affects brain function and cognitive performance. Caffeine can enhance performance and reduce perception of effort during prolonged exercise and will influence specific reward centers of the brain. Plant products and herbal extracts such as polyphenols, ginseng, ginkgo biloba, etc. are marketed as supplements to enhance performance. In several animal studies, positive effects of these products were shown, however the literature on their effects on sports performance is scarce. Polyphenols have the potential to protect neurons against injury induced by neurotoxins, suppress neuroinflammation, and to promote memory, learning, and cognitive function. In general, there remains a need for controlled randomized studies with a strong design, sufficient statistical power, and well-defined outcome measures before “claims” on its beneficial effects on brain functioning can be established.
Amy J. Hector and Stuart M. Phillips
There exists a large body of scientific evidence to support protein intakes in excess of the recommended dietary allowance (RDA) (0.8 g protein/kg/day) to promote the retention of skeletal muscle and loss of adipose tissue during dietary energy restriction. Diet-induced weight loss with as low as possible ratio of skeletal muscle to fat mass loss is a situation we refer to as high-quality weight loss. We propose that high-quality weight loss is often of importance to elite athletes in order to maintain their muscle (engine) and shed unwanted fat mass, potentially improving athletic performance. Current recommendations for protein intakes during weight loss in athletes are set at 1.6–2.4 g protein/kg/day. However, the severity of the caloric deficit and type and intensity of training performed by the athlete will influence at what end of this range athletes choose to be. Other considerations regarding protein intake that may help elite athletes achieve weight loss goals include the quality of protein consumed, and the timing and distribution of protein intake throughout the day. This review highlights the scientific evidence used to support protein recommendations for high-quality weight loss and preservation of performance in athletes. Additionally, the current knowledge surrounding the use of protein supplements, branched chain amino acids (BCAA), β-hydroxy β-methylbutyrate (HMB), and other dietary supplements with weight loss claims will be discussed.
Øyvind Skattebo and Thomas Losnegard
Purpose: To investigate variability, predictability, and smallest worthwhile performance enhancement in elite biathlon sprint events. In addition, the effects of race factors on performance were assessed. Methods: Data from 2005 to 2015 including >10,000 and >1000 observations for each sex for all athletes and annual top-10 athletes, respectively, were included. Generalized linear mixed models were constructed based on total race time, skiing time, shooting time, and proportions of targets hit. Within-athlete race-to-race variability was expressed as coefficient of variation of performance times and standard deviation (SD) in proportion units (%) of targets hit. The models were adjusted for random and fixed effects of subject identity, season, event identity, and race factors. Results: The within-athlete variability was independent of sex and performance standard of athletes: 2.5–3.2% for total race time, 1.5–1.8% for skiing time, and 11–15% for shooting times. The SD of the proportion of hits was ∼10% in both shootings combined (meaning ±1 hit in 10 shots). The predictability in total race time was very high to extremely high for all athletes (ICC .78–.84) but trivial for top-10 athletes (ICC .05). Race times during World Championships and Olympics were ∼2–3% faster than in World Cups. Moreover, race time increased by ∼2% per 1000 m of altitude, by ∼5% per 1% of gradient, by 1–2% per 1 m/s of wind speed, and by ∼2–4% on soft vs hard tracks. Conclusions: Researchers and practitioners should focus on strategies that improve biathletes’ performance by at least 0.8–0.9%, corresponding to the smallest worthwhile enhancement (0.3 × within-athlete variability).
Karin Lobenius-Palmér, Birgitta Sjöqvist, Anita Hurtig-Wennlöf and Lars-Olov Lundqvist
This study compared accelerometer-assessed habitual physical activity (PA), sedentary time, and meeting PA recommendations among 102 youth with disabilities (7–20 years) in four subgroups—physical/visual impairments, intellectual disability, autism spectrum disorders, and hearing impairment—and 800 youth with typical development (8–16 years). Low proportions of youth with disabilities met PA recommendations, and they generally were less physically active and more sedentary than youth with typical development. The hearing impairment and autism spectrum disorder groups were the most and least physically active, respectively. Older age and to some extent female sex were related to less PA and more sedentary time. Considering the suboptimal levels of PA in youth with disabilities, effective interventions directed at factors associated with PA among them are needed.
Kelly P. Arbour-Nicitopoulos, Viviane Grassmann, Krystn Orr, Amy C. McPherson, Guy E. Faulkner and F. Virginia Wright
The objective of this study was to comprehensively evaluate inclusive out-of-school time physical activity programs for children/youth with physical disabilities. A search of the published literature was conducted and augmented by international expertise. A quality appraisal was conducted; only studies with quality ratings ≥60% informed our best practice recommendations. Seventeen studies were included using qualitative (n = 9), quantitative (n = 5), or mixed (n = 3) designs. Programs had a diversity of age groups, group sizes, and durations. Most programs were recreational level, involving both genders. Rehabilitation staff were the most common leaders. Outcomes focused on social skills/relationships, physical skill development, and psychological well-being, with overall positive effects shown in these areas. The best practice recommendations are consistent with an abilities-based approach emphasizing common group goals and interests; cooperative activities; mastery-oriented, individualized instruction; and developmentally appropriate, challenging activities. Results indicate that inclusive out-of-school time physical activity programs are important for positive psychosocial and physical skill development of children/youth with physical disabilities.
Stephen Crowcroft, Erin McCleave, Katie Slattery and Aaron J. Coutts
To assess measurement sensitivity and diagnostic characteristics of athlete-monitoring tools to identify performance change.
Fourteen nationally competitive swimmers (11 male, 3 female; age 21.2 ± 3.2 y) recorded daily monitoring over 15 mo. The self-report group (n = 7) reported general health, energy levels, motivation, stress, recovery, soreness, and wellness. The combined group (n = 7) recorded sleep quality, perceived fatigue, total quality recovery (TQR), and heart-rate variability. The week-to-week change in mean weekly values was presented as coefficient of variance (CV%). Reliability was assessed on 3 occasions and expressed as the typical error CV%. Week-to-week change was divided by the reliability of each measure to calculate the signal-to-noise ratio. The diagnostic characteristics for both groups were assessed with receiver-operating-curve analysis, where area under the curve (AUC), Youden index, sensitivity, and specificity of measures were reported. A minimum AUC of .70 and lower confidence interval (CI) >.50 classified a “good” diagnostic tool to assess performance change.
Week-to-week variability was greater than reliability for soreness (3.1), general health (3.0), wellness% (2.0), motivation (1.6), sleep (2.6), TQR (1.8), fatigue (1.4), R-R interval (2.5), and LnRMSSD:RR (1.3). Only general health was a “good” diagnostic tool to assess decreased performance (AUC –.70, 95% CI, .61–.80).
Many monitoring variables are sensitive to changes in fitness and fatigue. However, no single monitoring variable could discriminate performance change. As such the use of a multidimensional system that may be able to better account for variations in fitness and fatigue should be considered.
Anna E. Saw, Michael Kellmann, Luana C. Main and Paul B. Gastin
Athlete self-report measures (ASRM) have the potential to provide valuable insight into the training response; however, there is a disconnect between research and practice that needs to be addressed; namely, the measure or methods used in research are not always reflective of practice, or data primarily obtained from practice lacks empirical quality. This commentary reviews existing empirical measures and the psychometric properties required to be considered acceptable for research and practice. This information will allow discerning readers to make a judgment on the quality of ASRM data being reported in research papers. Fastidious practitioners and researchers are also provided with explicit guidelines for selecting and implementing an ASRM and reporting these details in research papers.