Current Issues in Sports Nutrition

Editor(s): A. Jeukendrup.

Caffeine and Creatine Use in Sport Is Drinking to Thirst Optimum? The Myths Surrounding Pre-Exercise Carbohydrate Feeding Nutrition in Team Sports Exercise, Appetite and Appetite-Regulating Hormones: Implications for Food Intake and Weight Control Nutrition for Acute Exercise-Induced Injuries


Subject index

Caffeine and Creatine Use in Sport Is Drinking to Thirst Optimum? The Myths Surrounding Pre-Exercise Carbohydrate Feeding Nutrition in Team Sports Exercise, Appetite and Appetite-Regulating Hormones: Implications for Food Intake and Weight Control Nutrition for Acute Exercise-Induced Injuries

Caffeine and Creatine Use in Sport

Author(s): M. A. Tarnopolsky

Background/Aims: Caffeine and creatine are 2 of the most widely available and used compounds in sport. Although the use of either is not considered a doping infraction, the evidence does suggest ergogenic potential in certain sports. The purpose of this paper is to review the pharmacology and potential mechanism(s) of action of caffeine and creatine as they pertain to possible use as an ergogenic aid in sport. Methods: Previous review articles on caffeine and creatine use in sport were screened for relevant information and references, and studies for review and recent articles (2007 onwards) were obtained and reviewed using a PUBMED search with the terms ‘caffeine AND exercise’, ‘creatine and creatine monohydrate AND exercise’, and appropriate linked articles were evaluated. Results: Caffeine taken before (3–6 mg/kg) or during (1–2 mg/kg) endurance exercise enhances performance, through central nervous system and direct muscle effects. Creatine monohydrate supplementation at higher (approx. 20 g/day × 3–5 days) or lower (approx. 5 g/day × 30 days) doses increases skeletal muscle total and phosphocreatine by 10–20%. Creatine supplementation appears to minimally but significantly enhance high-intensity sport performance and the mass and possibly strength gains made during resistance exercise training over the first few months. Conclusions: Although caffeine and creatine appear to be ergogenic aids, they do so in a sport-specific context and there is no rationale for their simultaneous use in sport. Higher doses of caffeine can be toxic and appear to be ergolytic. There is no rationale for creatine doses in excess of the recommendations, and some athletes can get stomach upset, especially at higher creatine doses.

Is Drinking to Thirst Optimum?

Author(s): T.D. Noakes

Backgrounds/Aims: Prior to 1969, athletes were advised to avoid drinking during exercise. At least 4 subsequent events led to the adoption of a radically different approach. By 1996, all exercisers were advised to drink ‘as much as tolerable’ in order to insure that they did not lose any weight during exercise – the ‘zero percent dehydration’ doctrine. This advice requires that athletes drink enough to ‘stay ahead of thirst’. The act of drinking is a basic survival instinct that has been regulated by complex, unconscious controls ever since the first fish-like creatures moved onto land and should not require conscious adjustment. Methods: Literature survey of all studies comparing the effects of drinking to thirst (ad libitum) and drinking to prevent any weight loss during exercise – the ‘zero percent dehydration’ doctrine. Result: No study found that drinking more than ad libitum during exercise produced any biological advantage, but it could cause exercise-associated hyponatremia. Conclusion: Drinking ad libitum appears to optimize performance and safety during exercise in many situations. The presence of thirst, not of water loss, may be the biological signal that impairs exercise performance in those who drink less than their thirst dictates during exercise.

The Myths Surrounding Pre-Exercise Carbohydrate Feeding

Author(s): A.E. Jeukendrup, S.C. Killer

Background/Aims: Carbohydrate ingested 30–60 min before exercise may result in hypoglycaemia during exercise, a phenomenon often called rebound or reactive hypoglycaemia. There is considerable confusion regarding pre-exercise carbohydrate feeding with advice that ranges from ‘consume carbohydrate in the hour before exercise’ to ‘avoid carbohydrate in the 60 min prior to exercise’. Methods: We analysed the studies available in the literature to draw conclusions about the use of carbohydrate in the pre-exercise period. Results: Without performing a meta-analysis, it is clear that the risk of reduced performance is minimal as almost all studies point towards unaltered or even improved performance. This is despite the rather large metabolic changes that occur in response to pre-exercise carbohydrate feeding. Conclusion: It can be concluded that advice to avoid carbohydrate feeding in the hour before exercise is unfounded. Nevertheless athletes may develop symptoms similar to those of hypoglycaemia, even though they are rarely linked to actual low glucose concentrations. An individual approach may therefore be necessary to minimize these symptoms even though they do not appear to be related to exercise performance.

Nutrition in Team Sports

Author(s): I. Mujikaa, L.M. Burkec

Team sports are based on intermittent high-intensity activity patterns, but the exact characteristics vary between and within codes, and from one game to the next. Despite the challenge of predicting exact game demands, performance in team sports is often dependent on nutritional factors. Chronic issues include achieving ideal levels of muscle mass and body fat, and supporting the nutrient needs of the training program. Acute issues, both for training and in games, include strategies that allow the player to be well fuelled and hydrated over the duration of exercise. Each player should develop a plan of consuming fluid and carbohydrate according to the needs of their activity patterns, within the breaks that are provided in their sport. In seasonal fixtures, competition varies from a weekly game in some codes to 2–3 games over a weekend road trip in others, and a tournament fixture usually involves 1–3 days between matches. Recovery between events is a major priority, involving rehydration, refuelling and repair/adaptation activities. Some sports supplements may be of value to the team athlete. Sports drinks, gels and liquid meals may be valuable in allowing nutritional goals to be met, while caffeine, creatine and buffering agents may directly enhance performance.

Exercise, Appetite and Appetite-Regulating Hormones: Implications for Food Intake and Weight Control

Author(s): D. Stensel

Knowledge about the relationship between exercise and appetite is important both for athletes wishing to optimise performance and for those interested in maintaining a healthy body weight. A variety of hormones are involved in appetite regulation including both episodic hormones, which are responsive to episodes of feeding, and tonic hormones, which are important regulators of energy storage over the longer term (e.g. insulin and leptin). Notable among the episodic appetite-regulating hormones is ghrelin, which plays a unique role in stimulating appetite and energy intake. Many studies have demonstrated that acute bouts of moderately vigorous exercise transiently suppress appetite and this has been termed ‘exercise-induced anorexia’. The mechanisms by which acute exercise suppresses appetite are not fully understood but may involve lowered concentrations of ghrelin and increased concentrations of satiety hormones, notably peptide YY and glucagon-like peptide 1. Evidence suggests that chronic exercise training typically causes a partial but incomplete compensation in energy intake perhaps due to beneficial changes in appetite-regulating hormones. The lack of a full compensatory response of appetite to exercise may facilitate the development of a negative energy balance and weight loss although there is individual variability in the response to exercise. From a practical standpoint athletes should not feel concerned that exercise will cause overeating as there is limited evidence to support this. For those desiring weight loss there may be some merit in performing exercise in the postprandial period as a means of enhancing the satiating effect of a meal but additional evidence is required to confirm the effectiveness of this strategy.

Nutrition for Acute Exercise-Induced Injuries

Author(s): K.D. Tipton

Background/Aims: Injuries are an unavoidable aspect of participation in physical activity. Little information about nutritional support for injuries exists. Review: Immediately following injury, wound healing begins with an inflammatory response. Excessive anti-inflammatory measures may impair recovery. Many injuries result in limb immobilization. Immobilization results in muscle loss due to increased periods of negative muscle protein balance. Oxidative capacity of muscle is also decreased. Nutrient and energy deficiencies should be avoided. Energy expenditure may be reduced during immobilization, but inflammation, wound healing and the energy cost of ambulation limit the reduction of energy expenditure. There is little rationale for increasing protein intake during immobilization. There is a theoretical rationale for leucine and omega-3 fatty acid supplementation to help reduce muscle atrophy. During rehabilitation and recovery from immobilization, increased activity, in particular resistance exercise will increase muscle protein synthesis and restore sensitivity to anabolic stimuli. Ample, but not excessive, protein and energy must be consumed to support muscle growth. During rehabilitation and recovery, nutritional needs are very much like those for any athlete desiring muscle growth. Conclusion: Nutrition is important for optimal wound healing. The most important consideration is to avoid malnutrition and to apply a risk/benefit approach.