Various types of protein supplements are available. They are usually sold as a means of increasing muscle bulk, sometimes as protein powders alone, sometimes with added carbohydrate. Some research supports the anabolic (muscle-building) effects of consuming about 2.0-2.5 g of protein per kilogram of body weight each day during resistance training by athletes who compete in strength/power events. However, because they have relatively high energy requirements, eating a balanced diet usually supplies all the protein they need. There is no conclusive evidence to suggest that taking protein supplements will enhance muscle mass in athletes who are eating well and doing high-quality resistance training.
This particular type of protein is a by-product of the cheese-making industry. The liquid left after the cheese curd is separated contains protein, which, it has been suggested, has a high biological value (i.e. it is a relatively “complete” protein and is easily used by the body) and promotes gains in muscle mass greater than other protein supplements. The studies demonstrating that whey protein builds muscle have mostly been done in animals. Evidence for any effect on performance related to muscle building in humans is limited.
Another proposed positive effect of consumption of whey protein is that it may enhance immune function. It is suggested that, because whey contains significant amounts of the amino acid cysteine, it promotes the production of an antioxidant, glutathione, which is necessary for development of the immune response. There is not a lot of scientific evidence for this, and again most studies have ben done in animals, but one study showed an increase in peak power, 30-second work capacity, and glutathione levels when 18 athletes were supplemented with 20 g of whey protein per day. The authors suggest that the whey protein reduced oxidative stress and muscle fatigue.
Not all whey protein is the same. Different methods of processing affect the amount and nature of the protein. Whey protein hydrolysate is considered inferior, as the protein is denatured by heat processing during preparation. Whey protein isolate (the most expensive type) contains most protein (about 90 g per 100 g), whereas whey protein concentrate contains less than half this (35 g per 100 g). Whey protein prepared using long-exchange filtration appears to retain most of the supposed immune-enhancing components. Thus, those wishing to gain the proposed immune system benefits should choose whey isolates prepared by ion-exchange filtration.
Chromium is a trace element that is involved in insulin action and maintaining blood sugar levels. Athletes appear to have increased urinary excretion of the mineral compared with sedentary adults. Chromium, usually as chromium picolinate, which is easily absorbed, is taken by some athletes in the belief that it will increase strength. Scientific evidence of this is equivocal.
This is a naturally occurring amino acid (methyl-guanidine acetic acid) found in skeletal muscles. It is made in the body from other amino acids, but is also present in meat. The average adult daily requirement is thought to be about 2 g: about 1 g of this is supplied by the diet in meat-eaters, but must be produced endogenously by vegetarians. In muscle, in the form of creatine phosphate, creatine provides a source of fuel for sprints or high-intensity exercise lasting up to 10 seconds.
Creatine monohydrate is the most common dietary supplement and it has been shown that large doses will increase muscle creatine and creatine phosphate. The response to creatine supplementation is variable, and about 30% of people will not show increased levels sufficient to improve performance, possibly because the levels in muscle were high to begin with. Creatine supplementation has been shown to enhance performance in exercise involving repeated sprints or bouts of high-intensity exercise followed by short recovery intervals. It has also been shown in some studies to increase strength. Athletes taking this supplement will be given a loading protocol, whereby the muscle levels are built up to saturation, followed by a daily small dose to maintain levels. Some studies suggest that carbohydrate taken with the creatine will enhance uptake into muscles. No long-term studies of creatine supplementation have been reported but as yet no adverse effects have been described.
This is an amino acid that acts as fuel for the immune system. Athletes who are training hard have been shown to have low circulating levels of glutamine in the hours after hard exercise.
Although exercise is generally beneficial to health, it has been suggested that athletes in heavy training, or who have recently completed an endurance event, are more susceptible to infections than sedentary people. It is possible that severe exercise results in a temporary reduction in the body’s immune response. It has been proposed that the reduction in circulating glutamine may result in a reduced ability to mount an immune response to opportunistic infections. Experimental work investigating the idea that glutamine supplements may protect athletes from infections has not yet been conclusive. However, the supplements are sold widely and research is ongoing.
These are drinks that are designed to enable athletes to replace fluid lost during exercise. Dehydration can affect athletic performance, especially in endurance exercise such as long-distance running, but also in sports such as football or tennis where there is intermittent high-intensity exercise.
Sports drinks usually contain sugars (often as glucose) and electrolytes (sodium and potassium), but may also contain other substances such as choline and glycerol. They are designed with specific concentrations of glucose and electrolytes that are said to allow optimal rates of fluid absorption. The carbohydrate is also a source of energy. Concentrated solutions of carbohydrate can cause gastrointestinal upsets in some people.
Glycerol added to sports drinks has been shown in some studies, but not others, to enhance fluid absorption and prevent fatigue. It may be useful in endurance exercise, especially in hot conditions, but it may cause headaches and nausea, and is not advisable for those with high blood pressure or kidney problems, or for pregnant women.