Understanding how different nutrients can enhance exercise performance has led to the development of specific sports foods, where nutrients are packaged in convenient forms for athletes and exercising individuals. Sports drinks, gels, bars and dietary supplements in liquid, powder or capsule form are frequently used by athletes and exercising individuals. The vast majority of these specialised sports foods are simply convenient packages of nutrients, but athletes can often receive the same benefits from consuming these nutrients in regular foods, which may also provide a cheaper alternative. Nevertheless, sports foods can have a role to play in an athlete’s diet. For example, we know that consuming protein after resistance exercise enhances muscle protein synthesis. Most foods that are high in protein such as meat, poultry, eggs and dairy foods require refrigeration and are not always easy to access after a training session. A sports food such as a protein powder that can be mixed with water may be more convenient for an athlete to take to training and consume immediately after they finish exercise.
Nutritional ergogenic aids or sports supplements are dietary supplements that enhance performance above levels anticipated under normal conditions. Ergogenic aids typically contain unusual amounts of nutrients or other components of foods that would not normally be consumed through food alone. There are many products available today that are marketed as being able to enhance exercise performance, but there is rarely strong scientific evidence to support the proposed benefits. Nevertheless, the way in which many ergogenic aids are marketed make them very attractive for athletes and exercising individuals. In fact, many athletes hold strong beliefs about the positive effects of certain ergogenic aids. This may be due to a genuine benefit, or it may be due to a placebo or belief effect. The placebo effect occurs when an individual experiences or perceives a benefit from an ergogenic aid due to the belief that it will be beneficial rather than any direct physiological effect. Many scientists discount placebo effects as not being real and these effects are often tightly controlled for in experiments evaluating the effectiveness of an ergogenic aid. However, there have also been well controlled studies investigating the placebo effect using ergogenic aids such as caffeine that are known to enhance performance. These studies have shown that exercise performance is enhanced when participants are told they are receiving the ergogenic aid despite only being given an inactive substance rather than the actual ergogenic aid. Interestingly, although the placebo effect enhances performance, the magnitude of this effect is usually slightly less than the amount of performance improvement observed from the actual ergogenic aid. Some placebo effects are likely to occur with ergogenic aids and this may have some implications for ethical practice in sports nutrition. It might not be considered ethical to deliberately deceive an athlete by advising them to consume an ergogenic aid that does not cause any physiological effects which enhance performance. However, most athletes want to perform at their best regardless of how that is achieved and are more than willing to consume ergogenic aids even if the benefits are only due to a placebo effect. This area is complex, but the placebo effect should be taken into consideration when providing advice about ergogenic aids and also when monitoring the effects of ergogenic aids in sport. Despite many ergogenic aids not having scientific evidence to support their marketing claims, there are still a number of ergogenic aids that have actually been shown to be effective at enhancing performance under certain conditions and these include caffeine, creatine, nitrates, bicarbonate and beta-alanine.
Caffeine is one of the most widely used pharmacologically active substances in the world and it has been shown to improve performance in a variety of exercise tasks. Caffeine is present in many commonly consumed foods and beverages such as coffee, tea, chocolate and cola flavoured beverages. The physiological effects of caffeine occur due to its similarity to the adenosine molecule. Among its many actions, adenosine causes a decrease in alertness and arousal when it binds to receptors on the surface of cells in the brain. Caffeine also binds to these receptors and blocks the effects of adenosine. Therefore, caffeine can increase alertness, arousal and subsequently reduces the perception of effort during exercise. The reduced perception of effort during exercise can enhance performance by delaying fatigue and allowing an athlete to exercise at a higher intensity for longer periods of time.
Interestingly, the dose of caffeine required to achieve optimal improvements in exercise performance is relatively small. Doses of approximately 3 mg/kg body mass appear to be most effective with no additional benefit occurring with higher doses. This dose is equivalent to approximately 600 ml of a standard energy drink or two cups of coffee and is actually quite similar to the usual daily consumption of caffeine for many adults. Consumption of caffeine at these relatively low doses is unlikely to result in any negative side effects in most people, which is perhaps one reason why caffeine use in sport has not been restricted since 2004. Caffeine has been shown to improve performance when consumed in tablet form, coffee or in energy drinks. However, the amount of caffeine in coffee can vary significantly. In fact, some Australian studies have shown that there is a ten-fold difference in the caffeine content of coffee purchased at different retail outlets. Using energy drinks as a source of caffeine can also have limitations for athletes. Some athletes experience uncomfortable gastrointestinal symptoms when energy drinks are consumed before exercise. Therefore, it is recommended that caffeine is consumed in tablet form when used as a sports supplement in order to be most certain of the exact dose ingested and also to reduce any unwanted gastrointestinal side effects.
Caffeine is most effective when consumed approximately one hour before exercise, although many studies have shown caffeine enhances performance when it is given to participants at a variety of different times before and/or during the exercise task. It has even been shown that very small amounts of caffeine consumed in cola beverages can enhance performance in the concluding stages of an endurance exercise task. The benefit to performance in this instance actually occurred despite very little change in the caffeine concentration in the blood. In fact, the amount of caffeine appearing in the blood does not seem to be related to the performance benefit. Nevertheless, the studies that have directly compared different times of ingestion suggest that approximately one hour before exercise is optimal, but there may well be variations to this for different individuals.
Contrary to popular belief, caffeine consumption does not cause dehydration during exercise. Even though caffeine acts as a mild diuretic by causing small increases in urine volume, these effects are negated by exercise, possibly due to the changes in hormones and cardiovascular function during exercise. In fact, caffeine has actually been shown to cause similar performance benefits when consumed before exercise performed in hot conditions compared with more neutral environmental conditions.
Regular consumption of caffeine can cause the body’s cells to adapt and generate more adenosine receptors. This has the potential to make regular caffeine consumer less able to experience the performance enhancements associated with caffeine supplementation. However, studies have shown that individuals who normally consume large amounts of caffeine in their diet still receive similar benefits when consuming caffeine before exercise compared with athletes who do not consume much caffeine on a regular basis. It also does not appear that there is any benefit gained from abstaining from caffeine for a few days before using a caffeine supplement. It is important to note that, while we are confident caffeine supplementation is effective at improving exercise performance, there are a limited number of studies that have thoroughly investigated the factors that might moderate the ergogenic effects of caffeine and more research in this area is certainly warranted.
Creatine has been used by athletes as an ergogenic aid for several decades. Supplementation with creatine monohydrate increases the creatine pool in muscles which allows for more rapid ATP regeneration during repeated bouts of high intensity exercise. This mechanism may enable a higher training intensity and improved adaptation to training, particularly resistance training which involves repeated, high force muscle contractions. Creatine supplementation also appears to positively influence anabolic processes in muscles which result in an increase in lean muscle mass after supplementation. Many studies have shown that creatine supplementation during a period of resistance training enhances gains in muscle strength and lean body mass. Typical creatine supplementation protocols involve a short loading phase lasting 5-7 days in which 20g/day of creatine monohydrate is consumed in 4 daily intakes of 5g each, evenly spaced throughout the day. This is then followed by a maintenance phase in which 3-5g/day is consumed. The maintenance phase typically lasts for the duration of the training cycle in which improvements in maximal muscle strength and lean body mass are the primary goals.
Dietary nitrate is becoming increasingly popular as a sports supplement due to its capacity to enhance endurance exercise performance. Many green leafy vegetables and beetroot are examples of foods with a high nitrate content. The nitrate content of foods can vary significantly due to growing conditions and loss of nitrate during cooking and preparation which makes it difficult to predict how much dietary nitrate is being consumed through different foods. There are now many sports foods and beverages available that are made with concentrated beetroot juice and contain a known amount of nitrate. Once ingested, dietary nitrate can be converted to nitrite by bacteria in the mouth. Circulating nitrite is then converted into nitric oxide in blood and other tissues. Enhancing nitric oxide availability may improve muscle function and consequently exercise performance. Nitrate supplementation appears to specifically enhance the efficiency of oxygen use during exercise which allows individuals to perform greater work for the same energy cost. This results in an improved capacity to exercise at a fixed intensity for a longer duration before exhaustion occurs. Daily intake of 400-500mg of nitrate for approximately one week appears to be most effective at enhancing performance, however, benefits have also been shown after a single dose consumed 2-3 hours before exercise. Interestingly, the benefits of dietary nitrate supplementation are less evident in highly trained athletes, particularly when exercise performance is measured via a time-trial test rather than time to exhaustion tests. This suggests that recreational exercisers are likely to experience improved exercise performance after nitrate supplementation. However, elite athletes may wish to monitor their individual response to nitrate supplementation to determine if this is likely to be an effective nutrition strategy that contributes to their performance goals.
Performance in short duration, high intensity exercise can be improved after the ingestion of sodium bicarbonate. Increasing bicarbonate in the blood enhances the capacity to buffer acid produced by the muscle during exercise. This has the potential to delay fatigue during high intensity exercise. Although there is a clear mechanistic rationale for bicarbonate to enhance performance, not all studies show a performance benefit. This may be due to side effects associated with gastrointestinal discomfort off-setting the benefit of an improved buffer capacity. Similar to nitrate supplementation, the benefits of bicarbonate ingestion appear to be less evident in highly trained individuals, possibly due to the already high buffer capacity developed through training in this population. Doses of 200-400mg/kg body mass consumed 60-90 minutes before exercise appear to be optimal, however it is recommended that athletes trial this on several occasions during training to ensure that no adverse gastrointestinal side effects are likely to occur in competition.
Beta-alanine is a component of the dipeptide carnosine which plays a role in buffering acid produced in the muscle during high intensity exercise. This has the potential to delay fatigue and enhance performance, particularly in events lasting approximately 1-4 minutes in duration. Beta-alanine supplementation for several weeks has been shown to result in increased muscle carnosine and improved performance in short duration (1-4 minutes), high intensity exercise. A daily dose of 6.4g is used in most studies and it appears that at least 4 weeks of beta-alanine supplementation is required to elevate muscle carnosine concentration. However, further increases in muscle carnosine concentration are observed after 10 weeks of supplementation. The daily dose is usually consumed on 3-4 occasions spread throughout the day in order to reduce the acute side effects associated with consumption of large doses of beta-alanine. Side effects can include tingling, flushing and a prickly sensation on the skin which peak around 30-60 minutes after the ingestion of beta-alanine. The protocol for beta-alanine supplementation is much more difficult for athletes to adhere to than protocols for other supplements as it involves several daily doses taken for several weeks. Therefore, beta-alanine supplementation is only recommended for highly motivated athletes who are able to commit to a relatively long supplementation regime.
Supplements such as caffeine, creatine, nitrate, sodium bicarbonate and beta-alanine have all been shown to enhance exercise performance in many different studies. Most studies compare the effects of a single ergogenic aid against a placebo under relatively well-controlled conditions. However, many athletes looking for a competitive edge will consume multiple ergogenic aids at the same time in order to derive as much benefit as possible. Unfortunately, the beneficial effects of different supplements may not be additive when more than one is consumed. Findings of studies investigating combinations of supplements are somewhat inconsistent with some showing additive effects and other studies showing that performance gains from multiple supplements are no greater than those from a single supplement. Research into the effects of consuming multiple supplements is relatively scant at present due to the difficulty of conducting studies involving multiple interventions. While further research is required, it is also likely that different athletes will have somewhat different responses to each supplement. It is therefore important for athletes to monitor and evaluate their own individual responses to supplements to most effectively use sports supplements to enhance their performance.
Research into supplements continues to evolve and there are many new ergogenic aids that have showed promising results, but there is not quite enough scientific evidence available to date to provide clear recommendations. Examples of these ergogenic aids include – pickle juice to reduce muscle cramps; tart cherry juice to enhance recovery; citrulline, carnitine and quercetin for enhanced endurance performance; curcumin for reducing inflammation and enhancing recovery; and glutamine for enhancing immune function. All of these ergogenic aids have the potential to provide significant benefit, but the evidence is insufficient at the moment to be confident that most athletes will respond positively when these ergogenic aids are consumed.