Skip to main content Accessibility help
×
Home
Hostname: page-component-65d66dc8c9-f7c9f Total loading time: 0.511 Render date: 2021-09-29T00:04:19.140Z Has data issue: true Feature Flags: { "shouldUseShareProductTool": true, "shouldUseHypothesis": true, "isUnsiloEnabled": true, "metricsAbstractViews": false, "figures": true, "newCiteModal": false, "newCitedByModal": true, "newEcommerce": true, "newUsageEvents": true }

Nutrition for sports performance: issues and opportunities

Published online by Cambridge University Press:  17 October 2011

Ronald J. Maughan*
Affiliation:
School of Sport, Exercise and Health Sciences, Loughborough University, Leicestershire LE11 3TU, UK
Susan M. Shirreffs
Affiliation:
School of Sport, Exercise and Health Sciences, Loughborough University, Leicestershire LE11 3TU, UK
*
* Corresponding author: Professor Ronald J. Maughan, fax +44 1509 226301, email R.J.Maughan@lboro.ac.uk
Rights & Permissions[Opens in a new window]

Abstract

Diet can significantly influence athletic performance, but recent research developments have substantially changed our understanding of sport and exercise nutrition. Athletes adopt various nutritional strategies in training and competition in the pursuit of success. The aim of training is to promote changes in the structure and function of muscle and other tissues by selective modulation of protein synthesis and breakdown in response to the training stimulus. This process is affected by the availability of essential amino acids in the post-exercise period. Athletes have been encouraged to eat diets high in carbohydrate, but low-carbohydrate diets up-regulate the capacity of muscle for fat oxidation, potentially sparing the limited carbohydrate stores. Such diets, however, do not enhance endurance performance. It is not yet known whether the increased capacity for fat oxidation that results from training in a carbohydrate-deficient state can promote loss of body fat. Preventing excessive fluid deficits will maintain exercise capacity, and ensuring adequate hydration status can also reduce subjective perception of effort. This latter effect may be important in encouraging exercise participation and promoting adherence to exercise programmes. Dietary supplement use is popular in sport, and a few supplements may improve performance in specific exercise tasks. Athletes must be cautious, however, not to contravene the doping regulations. There is an increasing recognition of the role of the brain in determining exercise performance: various nutritional strategies have been proposed, but with limited success. Nutrition strategies developed for use by athletes can also be used to achieve functional benefits in other populations.

Type
70th Anniversary Conference on ‘From plough through practice to policy’
Copyright
Copyright © The Authors 2011

Many different factors contribute to successful performance in sport. Among these, genetic endowment is undoubtedly the most important, but the innate sporting talent conferred by the genotype can be modified by various factors. Among these, a systematic programme of consistent and intensive training carried out over many years probably plays the greatest role. Successful athletes will possess the motivation to undertake this training, and tactics and other factors will also contribute. When all else is equal, however, as it usually is in elite sport which is structured in such a way that the outcome is always in doubt, an assortment of minor factors can determine who will be successful. Good food choices will not make a mediocre athlete into a champion, but poor food choices may prevent the potential champion from realising his/her potential.

Based on emerging evidence from nutrition science in the last two decades, there have been substantial changes in the approach to nutrition support of elite athletes. Until recently, the primary focus of sports nutrition was on recovery between training sessions to allow the athlete to undertake consistent intensive training without succumbing to injury, illness and chronic fatigue. This led to a particular focus on a high daily carbohydrate intake and high fluid intakes to ensure replacement of sweat losses. More recently, however, there has been a shift towards looking for ways in which sports nutrition can help promote the adaptations that take place in tissues in response to the training stimulus. Athletes still need energy, macronutrients and micronutrients, but sports nutrition is now more about using nutrition strategies to modulate training-induced muscle adaptations( Reference Hawley, Burke and Phillips 1 ).

A number of other new developments have arisen in sports nutrition. While each of these has attractions to the athlete in terms of the prospect of enhanced performance in competition, there are also opportunities to apply these same practices and principles to other population groups who have no interest in sport, but who may be physically active in their occupations, who may engage in exercise for the health benefits that ensue, or who may seek the improved functional outcomes that result (Table 1).

Table 1. Issues and opportunities from specific nutrition strategies that may apply to the elite athlete or to other population groups

There is also now a growing realisation that eating strategies for athletes must take account of the fact that each individual has different nutrition goals. At the elite level in sport, it is not acceptable any more to make generic prescriptions for all members of a team or for all competitors in any event. A strategy must be devised to take account of each athlete's physiological and biochemical characteristics as well as the training load and competition goals.

Building and repairing muscle

The aim of training is to improve exercise performance, and this is achieved by modulation of gene expression to induce changes in the structure and function of skeletal muscle and other tissues. The nature of the adaptation to training is specific to the nature of the stimulus applied: endurance training will enhance the capacity for endurance performance but elite athletes have low muscle strength( Reference Maughan, Watson and Weir 2 ) and highly trained strength athletes generally have poor endurance. The degree of response is proportional to the training load, i.e. to the intensity, duration and frequency of training. These responses to training are induced by selective alterations in the rates of synthesis and degradation of specific proteins: the tissue content of functional proteins is increased and the content of proteins that serve no functional role is decreased. The response is modulated by the nutrient, metabolic and hormonal environment, and this can be modified by food intake before, during and after training( Reference Phillips and van Loon 3 ). In this context, it is interesting to note that the 2011 list of prohibited substances and methods issued by the World Anti-Doping Agency includes, under Category M3, Gene Doping, the following prohibition( 4 ):

‘The following, with the potential to enhance sport performance, are prohibited:

3. The use of agents that directly or indirectly affect functions known to influence performance by altering gene expression.’

This clearly suggests that the use of nutrition manipulations that alter gene expression after training, and indeed training itself, are considered to be doping methods. It seems unlikely, however, that any athlete would be penalised for applying these methods.

Many athletes, especially those engaged in strength and power sports, consume a high-protein diet in the belief that this is necessary for muscle growth and repair, and the habitual protein intakes of some groups of athletes can reach values in excess of 2·5 g/kg body mass per d( Reference Tarnopolsky, Burke and Deakin 5 ), with some individual values far higher than this. However, while a diet deficient in protein will prevent muscle hypertrophy, very high dietary protein intakes will not drive the system in favour of protein synthesis. Excess protein will simply be used as a substrate for oxidative metabolism, either directly or as a precursor of glucose, and the excess nitrogen will be lost in the urine. All forms of exercise will cause an increased rate of protein oxidation compared with the resting state( Reference Millward 6 ), leading to an increase in the minimum daily protein requirement. Exercise, however, will increase the energy demand and any increased protein requirement will be met if a normal mixed diet adequate to meet the increased energy expenditure is consumed.

The timing of protein intake relative to training may be more important than the amount of protein consumed( Reference Phillips and van Loon 3 ). Remodelling of the muscle tissues takes place in the hours and days after the training stimulus has been applied: consumption of small amounts of protein can ensure positive protein balance. As little as 6 g essential amino acids or about 20 g high-quality mixed protein, ingested either just before or soon after training may help promote that the adaptations taking place within the muscles and further increases in the amount of protein ingested have little further effect( Reference Moore, Robinson and Fry 7 , Reference Glover and Phillips 8 ). Resistance training in the fasted state and without ingesting some protein-containing foods soon after training will not optimise the training response. Milk protein, especially whey, which is high in leucine, may be more effective than some other proteins in promoting net muscle protein synthesis after a resistance training session( Reference Phillips, Tang and Moore 9 ). Studies that have relied on net muscle protein balance as a marker for training adaptation have been criticised on the grounds that these short-term responses may not be predictive of longer term functional outcomes. The emerging evidence, however, does suggest that the acute responses observed in the few hours after a single resistance training session do translate into measurable effects on muscle mass and muscle strength that become measurable within a few weeks if the training and nutrition interventions are repeated a few times each week( Reference Phillips and van Loon 3 ). Some recent evidence suggests that it may be possible to simultaneously increase lean tissue mass while losing fat mass by combining a resistance exercise programme with intake of a fat-free milk drink after training: a matched group who consumed an isoenergetic carbohydrate drink after training gained a smaller amount of lean tissue mass and did not lose body fat( Reference Josse, Tang and Tarnopolsky 10 ). Subsequent to this observation in subjects undergoing resistance training, a similar effect has also been seen in overweight and obese individuals in the absence of exercise( Reference Baer, Stote and Paul 11 ): daily supplementation of the normal diet with 56 g whey protein for 23 weeks resulted in a mean reduction in body mass of 1·8 kg and in fat mass of 2·3 kg (suggesting a small gain in lean tissue mass), but supplementation with isoenergetic amounts of soya protein or carbohydrate had no effect.

Advances in molecular biology are beginning to clarify the intracellular mechanisms that underpin these adaptive responses. The mechanical and metabolic stresses of exercise cause changes in energy status and Ca concentrations in the active muscles and these activate or inhibit various signalling cascades that in turn affect the transcriptional co-activators that regulate gene expression. Coffey et al. showed an increased rate of myofibrillar protein synthesis, but no effect on mitochondrial protein synthesis, following high intensity sprint exercise when subjects ingested a protein–carbohydrate supplement (24 g whey protein, 4·8 g additional leucine and 50 g maltodextrin) 30 min prior to exercise: there was no effect on these signalling molecules when an energy-free placebo was ingested before exercise( Reference Coffey, Moore and Burd 12 ). A substantial increase in the phosphorylation of Akt-mTOR-S6K-rpS6 was observed in the fed trial, but there was no change in the placebo trial.

Moore et al. have recently used a unilateral exercise model to investigate the interactions between training and protein intake: resistance exercise followed by ingestion of 25 g whey protein was shown to stimulate myofibrillar protein synthesis over that induced by feeding alone( Reference Moore, Atherton and Rennie 13 ). This was attributed in part to greater phosphorylation of specific mammalian target of rapamycin signalling proteins (p70S6K and eEF2) and the activation of mitogen-activated protein kinases (extracellular-signal-regulated kinase 1/2 and p90RSK) signalling. Van Proeyen et al. looked at endurance rather than resistance training and showed that the acute response of the signalling proteins to a single bout of exercise is affected by nutrient status during training: 6 weeks of endurance training in the fed state (high carbohydrate pre-exercise meals and carbohydrate ingestion during exercise) resulted in slower re-activation of muscle protein translation than the same training regimen in the fasted state( Reference Van Proeyen, de Bock and Hespel 14 ). New training and nutrition strategies that maximise the adaptations taking place in the muscle will undoubtedly emerge as these mechanisms are further clarified.

These findings may have implications beyond the needs of athletes who wish to gain mass and strength. Disuse, whether due to a chronic condition or acute injury, leads to muscle wasting. The ageing process is also associated with loss of muscle mass and strength which may limit the ability to lead an independent life. Strategies to limit muscle loss and to maintain or restore function are therefore important. It is clear that the basic principles of exercise and nutrition that govern muscle responses to use and disuse are similar in athletes and in muscle-wasting conditions( Reference Phillips, Glover and Rennie 15 ). Recommendations aimed at maintaining function in the elderly differ in extent, but not in principle, from those aimed at athletes( Reference Morley, Argiles and Evans 16 ).

Low-carbohydrate, high-fat diets, performance and weight loss

The energy requirements of training are largely met by oxidation of fat and carbohydrate. The higher the intensity of exercise, the greater the reliance on carbohydrate as a fuel: at an exercise intensity corresponding to about 50% of an individual's maximum oxygen uptake (VO2 max), approximately two-thirds of the total energy requirement is met by fat oxidation, with carbohydrate oxidation supplying about one-third( Reference Romijn, Coyle and Sidossis 17 ). If the exercise intensity is increased to about 75% of VO2 max, the total energy expenditure is increased, and carbohydrate is now the major fuel. If carbohydrate is not available, or is available in only a limited amount, the intensity of the exercise must be reduced to a level where the energy requirement can be met by fat oxidation. The classic studies of Hultman, Bergstrom, Saltin and others in the 1960s clearly established the association between the availability of muscle glycogen and the capacity for endurance exercise( Reference Bergstrom, Hermansen and Hultman 18 ).

The practical message taken by coaches and athletes from these studies has been that carbohydrate intake should be sufficient to enable the training load to be sustained at the high level necessary to produce a response. During each strenuous training session, substantial depletion of the glycogen stores in the exercising muscles and in the liver takes place. If this carbohydrate reserve is not replenished by ingestion of high-carbohydrate foods before the next training session, training intensity must be reduced, leading to corresponding decrements in the training response. Any athlete training hard on a daily basis can readily observe this; if a low-carbohydrate diet, consisting mostly of fat and protein, is consumed after a day's training, it will be difficult to repeat the same training load on the following day. These observations led to the promotion of high-carbohydrate diets for all athletes in training. In a perceptive article written in 2000, however, Coyle wrote that ‘Although it is generally assumed that optimal adaptation to the demands of repeated training sessions requires a diet that can sustain muscle energy reserves, this premise does not consider the unsolved longstanding question of whether it is a lack or surplus of a substrate that triggers the training adaptation’( Reference Coyle 19 ). This comment was prompted by some recent studies suggested that training on a high-fat diet could increase the amount of fat oxidised during exercise but that it could also reduce the adaptations taking place within the muscle and potentially compromise the performance improvements that result from training( Reference Helge, Richter and Kiens 20 ).

Feeding a high-fat, low-carbohydrate diet for prolonged periods has been shown to increase the capacity of muscle to oxidise fat by stimulating mitochondrial biogenesis( Reference Hawley and Burke 21 ). This can certainly improve endurance capacity in the rat, but may not be as effective in man; similarly short-term fasting increases endurance capacity in the rat, but generally results in a decreased exercise tolerance in man( Reference Maughan, Fallah and Coyle 22 ). The training diet, therefore should generally be high in carbohydrate, with a large proportion of total energy intake in the form of complex carbohydrates and simple sugars, though there may be advantages in restricting carbohydrate availability before and during some training sessions( Reference Hawley and Burke 21 ). Some long training sessions should perhaps be performed in a fasted or carbohydrate-depleted state to maximise the capacity for fat oxidation, but athletes should probably ensure that carbohydrate stores are replete for high intensity training sessions. Thus, a daily intake of 10 g/kg body mass or even more may be necessary for athletes during periods of intensive training( Reference Burke, Hawley and Wong 23 ). These high levels of intake are difficult to achieve without consuming large amounts of simple sugars and other compact forms of carbohydrate, as well as increasing the frequency of meals and snacks towards a ‘grazing’ eating pattern.

Failure to meet carbohydrate needs may also make the athlete more susceptible to minor infectious illnesses. Exercising with low carbohydrate reserves can result in increased levels of stress hormones, which in turn impairs the functional capacity of the immune system. While usually trivial in themselves, these illnesses can disrupt training and may prevent participation in important competitions( Reference Robson-Ansley, Gleeson and Ansley 24 ).

The possibility of increased fat oxidation during exercise is attractive to those who seek to use a modest exercise programme to reduce body fat content. While it is clear that exercising in the fasted state or while consuming a carbohydrate-restricted diet can increase fat oxidation( Reference Maughan, Williams and Campbell 25 ), this is usually accompanied by an increase in the subjective perception of effort, and the total amount of work done, and therefore the effect on energy balance, is likely to be less( Reference Hawley, Maughan and Burke 26 ). It is also not at present clear whether carbohydrate-restricted diets are successful in promoting weight loss: most reviews have concluded that they are not more effective than isoenergetic low-fat diets( Reference Astrup, Larsen and Harper 27 , Reference Nordmann, Nordmann and Briel 28 ). The increase in perceived effort associated with exercise in a carbohydrate-depleted state is also likely to discourage adherence to an exercise programme.

Hydration

There is scope for nutritional intervention during exercise only when the duration of events is sufficient to allow absorption of drinks or foods ingested and this usually means only in exercise lasting more than about 40–60 min. The rules of some sports also limit opportunities for ingestion of food or fluid. The primary aims must be to ingest a source of energy, usually in the form of carbohydrate, and fluid for replacement of water (and, when losses are high) of electrolytes, especially Na, lost as sweat. High rates of sweat secretion are necessary during hard exercise in order to limit the rise in body temperature which would otherwise occur. If the exercise is prolonged, this leads to progressive dehydration and loss of electrolytes. Fatigue towards the end of a prolonged event may result as much from the effects of dehydration as from substrate depletion. Beginning exercise in a dehydrated state is certainly harmful to performance of high intensity exercise( Reference Goulet, Lamontagne-Lacasse and Gigou 29 ) and to endurance performance( Reference Gigou, Lamontagne-Lacasse and Goulet 30 ).

Laboratory tests of exercise performance may not truly reflect the conditions of sports competition. The choice of exercise model is therefore important, and many studies now use tests that more closely simulate the demands of sport, including time trials and variable intensity exercise tests. It is also recognised that indoor exercise in still air on a treadmill or stationary ergometer may impose a much greater heat stress than exercise of comparable intensity in an outdoor environment at the same temperature and relative humidity( Reference Sawka and Noakes 31 ). In many exercise situations, it is not necessary to drink anything during exercise. Most athletes finish endurance events with some degree of dehydration, but some slower performers may consume fluid in excess of sweat losses. This is not helpful to performance and may in extreme cases lead to hyponatraemia, which is occasionally fatal( Reference Hew-Butler, Ayus and Kipps 32 ).

Even in apparently homogeneous populations exercising at similar intensities in the same environment, there is a large individual variability in both sweat rate and sweat composition, and so some individual prescription is necessary, and the composition of drinks to be taken during exercise should be chosen to suit individual circumstances( Reference Maughan and Shirreffs 33 ). Prescription of fixed rates of fluid intake is generally not helpful. During exercise in the cold, fluid replacement may not be necessary as sweat rates will be low, but there is still a need to supply additional glucose to the exercising muscles. Although consumption of a high-carbohydrate diet in the days prior to exercise should reduce the need for carbohydrate ingestion during exercise in events lasting less than about 2 h, it is not always possible to achieve this; competition on successive days, for example, may prevent adequate glycogen replacement between exercise periods. In this situation, more concentrated glucose drinks are to be preferred, and recent evidence supports the inclusion of glucose/fructose mixtures when high rates of carbohydrate delivery are needed( Reference Jeukendrup 34 ). These will supply more glucose, thus sparing the limited glycogen stores in the muscles and liver without overloading the body with fluid. In many sports, there is little provision for fluid replacement: participants in games such as football or hockey can lose large amounts of fluid, but replacement is possible only at the half-time interval. Cold drinks can enhance endurance performance in warm weather more effectively than warm drinks by acting as a heat sink to slow the rate of rise of core temperature( Reference Lee, Maughan and Shirreffs 35 , Reference Lee, Shirreffs and Maughan 36 ).

Sports drinks containing glycerol, which acts to expand the plasma volume, have been popular with some endurance athletes, but as of 1 January 2010, these fall within the prohibited list of the World Anti-Doping Agency, and so their use in competition is not permitted( 4 ). Many other compounds have similar effects, though, and it remains to be seen whether these will also be prohibited on the basis that they act through similar mechanisms.

In the post-exercise period, replacement of fluid and electrolytes can usually be achieved through the normal dietary intake. If there is a need to ensure adequate replacement before exercise is repeated, extra fluids should be taken and additional salt (NaCl) might usefully be added to food or drinks( Reference Shirreffs, Taylor and Leiper 37 ). The other major electrolytes, particularly K, Mg and Ca, are present in abundance in fruit and fruit juices. Salt or mineral supplements are not normally necessary, though some cases of muscle cramp may be associated with high salt losses and may be prevented by ingestion of drinks with moderate–high salt content( Reference Stofan, Zachwieja and Horswill 38 ).

Although the focus of most research on hydration and exercise has been on performance outcomes, this is of little relevance to the majority of active individuals who exercise for enjoyment or health reasons. Fatigue and discomfort are major obstacles to exercise participation for many who would benefit from a regular exercise programme. The subjective perception of effort is therefore an important consideration: if the exercise feels hard, the duration will often be cut short and adherence is likely to be poor. It is well recognised that the subjective rating of perceived exertion is higher when exercise is performed in warm environments than in cool environments( Reference Galloway and Maughan 39 ) and is also increased by even moderate levels of hypohydration( Reference Carvalho, Oliveira and Barros 40 ). Ensuring an adequate hydration status prior to exercise and ingestion of fluids during exercise to limit the development of hypohydration may therefore prove to be important elements of an exercise prescription.

Dietary supplements

With regular strenuous training, there must be an increased total energy intake to balance the increased energy expenditure. Provided that a reasonably varied diet is consumed, this will generally supply more than adequate amounts of protein, minerals, vitamins and other essential dietary components. Athletes who chronically restrict energy intake to limit body mass, and especially fat mass, may benefit from a broad spectrum of vitamin and mineral supplements. Athletes with limited finances, little interest in the foods they eat, or those lacking in food preparation skills may also fail to consume a varied diet. While supplements are no substitute for good dietary choices, they may have a use in some of these situations.

There are a few well-recognised exceptions to the generalisation about the value of dietary supplements in meeting micronutrient needs, including Fe, and, in the case of very active women, Ca. More recently, there has been considerable interest in the role of vitamin D beyond its well-recognised effects on bone metabolism. There is growing evidence that many athletes are vitamin D deficient or insufficient, especially those who train indoors, who wear protective clothing while outdoors or who live at high latitudes( Reference Larson-Meyer and Willis 41 ), but the issue of whether athletes should supplement with vitamin D is at present controversial. Although there is no good evidence that routine vitamin D supplementation is beneficial to athletes, there is some evidence from cross-sectional studies of an association between circulating vitamin D levels and athletic performance( Reference Cannell, Hillis and Sorenson 42 ). It therefore seems prudent to recommend that athletes seek professional help to monitor their serum vitamin D status.

A wide range of supplements is on sale to athletes, often with exaggerated claims of efficacy in enhancing performance in competition. Many of these are not supported by evidence of either their effects on performance or their safety when taken in high doses for prolonged periods( Reference Maughan, Depiesse and Geyer 43 ). Sports supplements that may be useful in helping the athlete meet nutritional goals during training and competition include sports drinks, high-carbohydrate supplements and liquid meal supplements. These are more expensive than everyday foods, but often provide a convenient and practical way of meeting dietary needs in a specific situation. There is good evidence for an ergogenic effect of a few supplements in some specific situations, including caffeine, creatine and bicarbonate or other buffering agents, possibly including β-alanine. Caffeine in relatively small doses, typically 2–4 mg/kg, can improve performance in a variety of exercise tasks, with greater effects generally seen in prolonged exercise, probably by actions on adenosine receptors in the central nervous system rather than on lipolysis as was previously thought( Reference Davis, Zhao and Stock 44 ). Creatine, in the form of creatine phosphate, acts as an energy source for ATP re-synthesis in high intensity exercise. Meat eaters normally obtain about 1 g creatine/d from their diet, which is about 50% of the daily requirement, with the remainder synthesised from amino acids. Ingestion of about 10–20 g creatine for a period of 4–6 d can increase the muscle creatine content by 10–20%, leading to improvements in strength and sprint performance( Reference Kreider 45 ). The biggest improvements in performance are generally seen in repeated sprints with limited recovery. Acute ingestion of large doses of NaHCO3 (about 0·3 g/kg) can increase the extracellular buffering capacity and improve performance in exercise lasting from about 30 s to about 10 min. Similar benefits may be seen from a few days of β-alanine supplementation, which leads to an increase in muscle carnosine content and hence in buffer capacity( Reference Sale, Saunders and Harris 46 ). Recent data suggest a beneficial effect on exercise performance of large doses of dietary nitrate, which have been shown to reduce the oxygen cost of exercise( Reference Larsen, Ekblom and Sahlin 47 , Reference Larsen, Schiffer and Bourniquet 48 ) and to improve performance( Reference Bailey, Winyard and Vanhatalo 49 ). Both inorganic nitrate and vegetable sources, such as beetroot juice, have been shown to be effective.

A concern with many supplements on sale, apart from the lack of evidence of efficacy and safety, is the recent spate of reports of contamination of supplements with prohibited substances, including stimulants and anabolic steroids( Reference Maughan 50 ). The amounts present are generally, though not always, too small to be effective in improving performance or to pose a risk to health but can cause a positive drugs test( Reference Watson, Houghton and Grace 51 ). In some cases, however, high doses, even higher than the normal therapeutic dose, of steroids, stimulants and anorectic agents have been found in supplements, not only with potential performance benefits but also with a real risk of adverse health effects. One of the best-selling supplements, hydroxycut, was withdrawn from sale in 2009 because of links with liver damage that reportedly led to at least one fatality( Reference Seminerio and Sweetser 52 ).

Nutrition and the brain

Anyone who is physically active is familiar with the sensations that accompany a bout of hard exercise: these generally include breathlessness and muscle discomfort or even pain. It is easy to ascribe the cause of fatigue in these situations to a limitation occurring at the level of the lungs or in the active muscles. There is considerable interest, however, in the possibility that exercise performance is limited by events within the brain. There is, of course, nothing new in this idea and in 1889, Lagrange wrote that ‘Fatigue is … a kind of regulator, warning us that we are exceeding the limits of useful exercise, and that work will soon become dangerous. Numerous physiological phenomena show us that the sensation of fatigue has its seat rather in the nerve-centres than in the muscles’( Reference Lagrange 53 ). The concept of a ‘central governor’ that is commonly ascribed to A.V. Hill was generally accepted long before his work on the nature and causes of muscular fatigue.

As well as being of interest to the scientist, this has, of course, implications for nutrition strategies that might affect performance. A century after Lagrange wrote the words quoted earlier, Newsholme et al. sought to identify a mechanism by which the brain might influence fatigue( Reference Newsholme, Acworth, Blomstrad and Benzi 54 ). Their central fatigue hypothesis was based on the role of the neurotransmitter serotonin (5-hydroxytryptamine) in symptoms of lethargy, low arousal, loss of motivation and increased sensation of effort, and they proposed that fatigue developed due to a reduced uptake into cerebral neurones of tryptophan, the metabolic precursor on 5-hydroxytryptamine. This elegant hypothesis was underpinned by well-recognised metabolic responses that would reduce the availability of tryptophan for uptake into active muscle during prolonged exercise. Support for this hypothesis has come from some, but not all, interventions that used drugs to manipulate 5-hydroxytryptamine activity in the brain( Reference Wilson and Maughan 55 , Reference Roelands and Meeusen 56 ) and there is a growing awareness that dopaminergic activity may be of major importance. Amphetamines, which act on dopamine receptors, have long been known to enhance exercise performance, and modern agents that have more specific actions are increasingly investigated for their actions on exercise performance( Reference Roelands and Meeusen 56 ). As mentioned earlier, it has also been shown that the action of caffeine in enhancing exercise performance may be mediated by actions on central adenosine receptors rather than by actions on muscle metabolism or contractility as was previously thought( Reference Davis, Zhao and Stock 44 ).

Although pharmacological agents have clear effects on exercise performance, nutritional interventions to induce changes in brain function by altering the availability of neurotransmitter precursors have generally not been successful, though there have been some exceptions. Mittleman et al. showed that ingestion of a moderate dose of branched-chain amino acids would prolong endurance capacity during cycling exercise in the heat( Reference Mittleman, Ricci and Bailey 57 ). This is consistent with the Newsholme hypothesis: an elevated plasma branched-chain amino acids concentration would compete with tryptophan for uptake into the brain. A recent report has suggested that pre-exercise ingestion of the amino acid tyrosine, a metabolic precursor of dopamine, can enhance endurance cycling performance in a warm (30°C) environment( Reference Tumilty, Davison and Meckman 58 ). It is notable that both of these studies involve a combination of prolonged exercise and heat stress, and the evidence for a role of central fatigue is greater in the heat than in cooler environments.

Central dopaminergic neurones are also implicated in a number of neurological disorders and in addictive behaviours, and recent studies suggest a role for exercise in the management of a range of clinical disorders( Reference Archer, Fredriksson and Johansson 59 ). There is also evidence from animal studies that habitually physically active animals may have an enhanced ability to increase DA synthesis, which may have implications for the supply of the tyrosine precursor( Reference Foley and Fleshner 60 ). There is clearly scope for interactive effects of nutrition and exercise and investigations in this area are currently in progress.

Acknowledgements

R. J. M. has acted over the last 30 years as a consultant to, and received research grant support from, many commercial and non-commercial organisations with sports nutrition interests. S. M. S. has acted over the last 15 years as a consultant to, and received research grant support from, many commercial and non-commercial organisations with sports nutrition interests. Both authors contributed fully to the preparation of this manuscript.

References

1. Hawley, JA, Burke, LM, Phillips, SM et al. (2011) Nutritional modulation of training-induced skeletal muscle adaptations. J Appl Physiol 110, 834845.CrossRefGoogle ScholarPubMed
2. Maughan, RJ, Watson, JS & Weir, J (1983) Relationships between muscle strength and muscle cross-sectional area in male sprinters and distance runners. Eur J Appl Physiol 50, 309319.CrossRefGoogle Scholar
3. Phillips, SM & van Loon, LJC (2011) Dietary protein for athletes: From requirements to optimum adaptation. J Sports Sci (In the Press).CrossRefGoogle ScholarPubMed
5. Tarnopolsky, M (2010) Protein and amino acid needs for training and bulking up. In Clinical Sports Nutrition , pp. 6195 [Burke, L and Deakin, V, editors]. Sydney: McGraw-Hill.Google Scholar
6. Millward, DJ (2003) An adaptive metabolic demand model for protein and amino acid requirements. Br J Nutr 90, 249260.CrossRefGoogle ScholarPubMed
7. Moore, DR, Robinson, MJ, Fry, JL et al. (2009) Ingested protein dose response of muscle and albumin protein synthesis after resistance exercise in young men. Am J Clin Nutr 89, 161168.CrossRefGoogle ScholarPubMed
8. Glover, EI & Phillips, SM (2010) Resistance exercise and appropriate nutrition to counteract muscle wasting and promote muscle hypertrophy. Curr Opinion Clin Nutr Metab Care 13, 630634.CrossRefGoogle ScholarPubMed
9. Phillips, SM, Tang, JE & Moore, DR (2009) The role of milk- and soy-based protein in support of muscle protein synthesis and muscle protein accretion in young and elderly persons. J Am Coll Nutr 28, 343354.CrossRefGoogle Scholar
10. Josse, AR, Tang, JE, Tarnopolsky, MA et al. (2010) Body composition and strength changes in women with milk and resistance exercise. Med Sci Sports Exerc 42, 11221130.Google ScholarPubMed
11. Baer, DJ, Stote, KS, Paul, DR et al. (2011) Whey protein but not soy protein supplementation alters body weight and composition in free-living overweight and obese adults. J Nutr 141, 14891494.CrossRefGoogle Scholar
12. Coffey, VR, Moore, DR, Burd, NA et al. (2011) Nutrient provision increases signalling and protein synthesis in human skeletal muscle after repeated sprints. Eur J Appl Physiol 111, 14731483.CrossRefGoogle ScholarPubMed
13. Moore, DR, Atherton, JR, Rennie, MJ et al. (2011) Resistance exercise enhances mTOR and MAPK signalling in human muscle over that seen at rest after bolus protein ingestion. Eur J Appl Physiol 111, 365372.Google Scholar
14. Van Proeyen, K, de Bock, K & Hespel, P (2011) Training in the fasted state facilitates re-activation of eEF2 activity during recovery from endurance exercise. Eur J Appl Physiol 111, 12971305.CrossRefGoogle ScholarPubMed
15. Phillips, SM, Glover, EI & Rennie, MJ (2009) Alterations of protein turnover underlying disuse atrophy in human skeletal muscle. J Appl Physiol 107, 645654.CrossRefGoogle ScholarPubMed
16. Morley, JE, Argiles, JM, Evans, WJ et al. (2010) Nutritional recommendations for the management of sarcopenia. J Am Med Dir Assoc 11, 391396.CrossRefGoogle ScholarPubMed
17. Romijn, JA, Coyle, EF, Sidossis, LS et al. (1993) Regulation of endogenous fat and carbohydrate metabolism in relation to exercise intensity and duration. Am J Physiol 265, E380E391.Google ScholarPubMed
18. Bergstrom, J, Hermansen, L, Hultman, E et al. (1967) Diet, muscle glycogen and physical performance. Acta Physiol Scand 71, 140150.CrossRefGoogle ScholarPubMed
19. Coyle, EF (2000) Physical activity as a metabolic stressor. Am J Clin Nutr 72, 512S520S.CrossRefGoogle ScholarPubMed
20. Helge, JW, Richter, EA & Kiens, B (1996) Interaction of training and diet on metabolism and endurance during exercise in man. J Physiol 492, 293306.CrossRefGoogle ScholarPubMed
21. Hawley, JA & Burke, LM (2010) Carbohydrate availability and training adaptation: Effects on cell metabolism and exercise capacity. Exerc Sport Sci Rev 38, 152160.CrossRefGoogle Scholar
22. Maughan, RJ, Fallah, JS & Coyle, EF (2010) The effects of fasting on metabolism and performance. Br J Sports Med 44, 490494.CrossRefGoogle ScholarPubMed
23. Burke, LM, Hawley, JA, Wong, S et al. (2011) Carbohydrates for training and competition. J Sports Sci (In the Press).CrossRefGoogle ScholarPubMed
24. Robson-Ansley, PJ, Gleeson, M & Ansley, L (2009) Fatigue management in the preparation of Olympic athletes. J Sports Sci 27, 14091420.CrossRefGoogle ScholarPubMed
25. Maughan, RJ, Williams, C, Campbell, DM et al. (1978) Fat and carbohydrate metabolism during low intensity exercise: Effects of the availability of muscle glycogen. Eur J Appl Physiol 39, 7–16.CrossRefGoogle ScholarPubMed
26. Hawley, JA (2011) Fat-adaptation science: Low-carbohydrate, high-fat diets to alter fuel utilization and promote training adaptation. In Sports Nutrition: More than Just Calories – Triggers for Adaptation, vol. 69.Nestlé Nutrition Institute Workshop Series [Maughan, RJ and Burke, LM, editors]. Basel: Karger AG (In the Press).Google Scholar
27. Astrup, A, Larsen, TM & Harper, A (2004) Atkins and other low-carbohydrate diets: Hoax or an effective tool for weight loss? Lancet 364, 897899.CrossRefGoogle ScholarPubMed
28. Nordmann, AJ, Nordmann, A, Briel, M et al. (2006) Effects of low-carbohydrate vs low-fat diets on weight loss and cardiovascular risk factors. Arch Intern Med 166, 285294.CrossRefGoogle ScholarPubMed
29. Goulet, EDB, Lamontagne-Lacasse, M, Gigou, P-Y et al. (2010) Pre-exercise hypohydration effects on jumping ability and muscle strength, endurance and anaerobic capacity: A meta-analysis. Med Sci Sports Exerc 42, S254.CrossRefGoogle Scholar
30. Gigou, P-Y, Lamontagne-Lacasse, M & Goulet, EDB (2010) Meta-analysis of the effects of pre-exercise hypohydration on endurance performance, lactate threshold and VO2 max. Med Sci Sports Exerc 42, S254.CrossRefGoogle Scholar
31. Sawka, MN & Noakes, TD (2007) Does dehydration impair exercise performance? Med Sci Sports Exerc 39, 12091217.CrossRefGoogle ScholarPubMed
32. Hew-Butler, T, Ayus, JC, Kipps, C et al. (2008) Consensus Statement of the 2nd International Exercise-Associated Hyponatremia Consensus Development Conference. Clin J Sports Med 18, 111121.CrossRefGoogle Scholar
33. Maughan, RJ & Shirreffs, SM (2008) Development of individual hydration strategies for athletes. Int J Sport Nutr Ex Metab 18, 457472.CrossRefGoogle ScholarPubMed
34. Jeukendrup, AE (2010) Carbohydrate and exercise performance: The role of multiple transportable carbohydrates. Curr Opin Clin Nutr Metab Care 13, 452457.CrossRefGoogle ScholarPubMed
35. Lee, JKW, Maughan, RJ & Shirreffs, SM (2008a) The influence of serial feeding of drinks at different temperatures on thermoregulatory responses during cycling. J Sports Sci 26, 583590.CrossRefGoogle ScholarPubMed
36. Lee, JKW, Shirreffs, SM & Maughan, RJ (2008b) Cold drink ingestion improves exercise endurance capacity in the heat. Med Sci Sports Exerc 40, 16371644.CrossRefGoogle ScholarPubMed
37. Shirreffs, SM, Taylor, AJ, Leiper, JB et al. (1996) Post-exercise rehydration in man: Effects of volume consumed and sodium content of ingested fluids. Med Sci Sports Exerc 28, 12601271.CrossRefGoogle Scholar
38. Stofan, JR, Zachwieja, JJ & Horswill, CC (2005) Sweat and sodium losses in NCAA football players: A precursor to heat cramps? Int J Sport Nutr Ex Metab 15, 641652.CrossRefGoogle ScholarPubMed
39. Galloway, SDR & Maughan, RJ (1997) Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man. Med Sci Sports Exerc 29, 12401249.CrossRefGoogle ScholarPubMed
40. Carvalho, P, Oliveira, B, Barros, R et al. (2011) Impact of fluid restriction and ad libitum water intake or an 8% carbohydrate-electrolyte beverage on skill performance of elite adolescent basketball players. Int J Sport Nutr Ex Metab 21, 214221.CrossRefGoogle ScholarPubMed
41. Larson-Meyer, DE & Willis, KS (2010) Vitamin D and athletes. Curr Sports Med Rep 9, 220226.CrossRefGoogle ScholarPubMed
42. Cannell, JJ, Hillis, BW, Sorenson, MB et al. (2009) Athletic performance and Vitamin D. Med Sci Sports Exerc 41, 11021110.CrossRefGoogle ScholarPubMed
43. Maughan, RJ, Depiesse, F & Geyer, H (2007) The use of dietary supplements by athletes. J Sports Sci 25, S103S113.CrossRefGoogle ScholarPubMed
44. Davis, JM, Zhao, ZW & Stock, HS (2003) Central nervous system effects of caffeine and adenosine on fatigue. Am J Physiol 284, R399R404.Google ScholarPubMed
45. Kreider, RB (2003) Effects of creatine supplementation on performance and training adaptations. Mol Cell Biochem 244, 8994.CrossRefGoogle ScholarPubMed
46. Sale, C, Saunders, B & Harris, RC (2010) Effect of beta-alanine supplementation on muscle carnosine concentrations and exercise performance. Amino Acids 39, 321333.CrossRefGoogle ScholarPubMed
47. Larsen, FK, Ekblom, B, Sahlin, K et al. (2007) Effects of dietary nitrate on oxygen cost during exercise. Acta Physiol 191, 5966.CrossRefGoogle ScholarPubMed
48. Larsen, FJ, Schiffer, TA, Bourniquet, S et al. (2011) Dietary inorganic nitrate improves mitochondrial efficiency in humans. Cell Metab 13, 149159.CrossRefGoogle ScholarPubMed
49. Bailey, SJ, Winyard, P, Vanhatalo, A et al. (2009) Dietary nitrate supplementation reduces the O2 cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans. J Appl Physiol 107, 11441155.CrossRefGoogle ScholarPubMed
50. Maughan, RJ (2005) Contamination of dietary supplements and positive drugs tests in sport. J Sports Sci 23, 883889.CrossRefGoogle Scholar
51. Watson, P, Houghton, E, Grace, PB et al. (2010) The effect of delivery mode on excretion patterns of nandrolone metabolites after ingestion of a nandrolone pro-hormone. Med Sci Sports Exerc 42, 754761.CrossRefGoogle Scholar
52. Seminerio, J & Sweetser, S (2010) Drug induced liver injury secondary to hydroxycut. Am J Gastroenterol 105, S270.Google Scholar
53. Lagrange, F (1889) Physiology of Bodily Exercise. London: Kegan, Paul, Trench.Google Scholar
54. Newsholme, EA, Acworth, I & Blomstrad, E (1987) Amino acids, brain neurotransmitters and a function link between muscle and brain that is important in sustained exercise. In Advances in Myochemistry , pp. 127133 [Benzi, G, editor]. London: Libby Eurotext.Google Scholar
55. Wilson, WM & Maughan, RJ (1992) A role for serotonin in the genesis of fatigue in man: Administration of a 5-hydroxytryptamine reuptake inhibitor (paroxetine) reduces the capacity to perform prolonged exercise. Exp Physiol 77, 921924.CrossRefGoogle Scholar
56. Roelands, B & Meeusen, R (2010) Alterations in central fatigue by pharmacological manipulations of neurotransmitters in normal and high ambient temperature. Sports Med 40, 229246.CrossRefGoogle ScholarPubMed
57. Mittleman, KD, Ricci, MR & Bailey, SP (1998) Branched-chain amino acids prolong exercise during heat stress in men and women. Med Sci Sports Exerc 30, 8391.CrossRefGoogle ScholarPubMed
58. Tumilty, L, Davison, G, Meckman, M et al. (2011) Oral tyrosine supplementation improves exercise capacity in the heat. Eur J Appl Physiol (In the Press).CrossRefGoogle ScholarPubMed
59. Archer, T, Fredriksson, A & Johansson, B (2011) Exercise alleviates Parkinsonism: Clinical and laboratory evidence. Acta Neurol Scand 123, 7384.CrossRefGoogle ScholarPubMed
60. Foley, TE & Fleshner, M (2008) Neuroplasticity of dopamine circuits after exercise: Implications for central fatigue. Neuromolecular Med 10, 6780.CrossRefGoogle ScholarPubMed
Figure 0

Table 1. Issues and opportunities from specific nutrition strategies that may apply to the elite athlete or to other population groups

You have Access
22
Cited by

Send article to Kindle

To send this article to your Kindle, first ensure no-reply@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about sending to your Kindle. Find out more about sending to your Kindle.

Note you can select to send to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

Find out more about the Kindle Personal Document Service.

Nutrition for sports performance: issues and opportunities
Available formats
×

Send article to Dropbox

To send this article to your Dropbox account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Dropbox.

Nutrition for sports performance: issues and opportunities
Available formats
×

Send article to Google Drive

To send this article to your Google Drive account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Google Drive.

Nutrition for sports performance: issues and opportunities
Available formats
×
×

Reply to: Submit a response

Please enter your response.

Your details

Please enter a valid email address.

Conflicting interests

Do you have any conflicting interests? *