Enhancing athletic performance

Sports supplements are promoted as a way to improve athletic performance. They aim to build muscle bulk, improve metabolism, replace meals or provide rapid replacement of fluid, energy and electrolytes lost by intense physical activity. These preparations are known as ergogenic (work-enhancing) aids.

Ergogenic supplements claimed to be based on nutritional principles include:

• protein powders

• amino acids

• meal replacements

• sports drinks.

Protein powders

Protein powders are intended to provide muscle bulk, but they supply no amino acids which are not present in food sources, and don’t contain any of the other nutrients needed to help build muscle tissue. After absorption, purified protein is used as an energy source or stored as fat.

Amino acids

Amino acid supplements claim to provide those most likely to be used as fuel in exercising muscles, but supply them in concentrations and combinations that can be difficult for the body to handle, with the danger of large doses forming substances which are toxic, especially to the brain.

In any case these supplements supply less fuel than glucose or fat, and are usually supplied abundantly in a normal diet, in a form that is readily and harmlessly metabolised.

A non-protein amino acid, carnitine, is taken by many endurance athletes in the belief that it will burn more fat and spare the muscle stores of glycogen. This action was not demonstrated in clinical tests, but it did produce diarrhoea in half of the athletes tested. Carnitine is supplied naturally in milk and meat products.

Meal replacements

Meal replacements are promoted as supplying the nutrients usually obtained from a single meal. They can be presented as a tasty food bar or in liquid form.

The bars are a convenient source of energy as a pre-game snack, but they are far from a ‘complete’ food, and not suitable as a meal replacement.

A liquid meal taken about two hours before an athletic event could be suitable for a nervous athlete who can’t tolerate solid food at this stage, but it does not supply all the nutrients you would expect from a meal. A drink blended from non-fat milk or soy drink with fruit can achieve the same result at a lower cost.

Sports drinks

Drinks especially for athletes are marketed as a way to replace water, energy and electrolytes lost during physical activity.

Water loss from activity occurs mainly through sweat. Replacement of water loss has a high priority where a period of intense activity is likely to last more than 30 minutes, especially in high temperatures.

Dehydration is the most likely factor to have an adverse effect on highenergy performance, causing fatigue and reducing the capacity to perform. If continued, it can result in heat stroke and collapse, which can be life-threatening.

What is the best way to replace water when exercising?

For people who are exercising moderately, plain cool water is recommended as a replacement fluid. It is rapidly absorbed and quickly transported to the tissues, to replace lost water and cool the body.

When do athletes need energy supplements?

Energy supplementation could be needed when events require continuous heavy muscle use for one hour or more. Stores of glycogen in muscle tissue are sufficient for shorter periods, where energy supplements would offer no advantage. Energy in sports drinks is usually supplied in the form of glucose or other simple sugars.

When sugar concentrations are higher than 10 per cent the transport of water to the tissues is reduced, which can result in muscle cramps and nausea. Less than 6 per cent would be unlikely to have any benefit for performance. Most sports drinks provide between 6–8 per cent sugar, which is about half of that found in normal soft drinks. However, some provide less and others exceed this range. The percentage of sugar in each product is listed on the label.

Energy intake from sports drinks and meal replacements can lead to fat deposits and risk of overweight when it contributes to a total energy intake in excess of output.

Why do athletes need electrolyte supplements?

Electrolytes in your body are the positive and negative ions formed when minerals dissolve in body fluids. Electrolytes are responsible for nerve impulses and the contraction and relaxation of muscle, including the heart muscle. The balance of electrolytes must be constantly maintained in order to perform these functions, and to prevent muscle cramps or irregularities in heartbeat.

Electrolytes are excreted from the body in sweat, which increases with exercise. In sustained heavy sweating there is rapid loss of electrolytes, especially sodium, and a high intake of plain water at the same time leads to dilution of sodium concentrations in the body. Sports drinks supply sodium and other electrolytes which can not only help to maintain balance, but also assist the rate of fluid absorption from the digestive tract.

However, immediate electrolyte replacement is not necessary in normal sporting activity. Strenuous, sustained exertion with heavy sweating can be maintained for up to six hours, with fluid loss being replaced by large amounts of plain water, before electrolyte dilution reaches dangerous levels.

Sodium concentration in sports drinks is low, so there is little risk of excessive intake when they are taken in conjunction with vigorous, high sweat activity.