Sports drinks
Studies have shown that the optimal means of replacing the fuel and fluid lost during exercise is through consumption of sports drinks, in particular those that are ‘isotonic’ (9). These have a carbohydrate content of between 4% and 8%, as well as electrolytes – primarily sodium and potassium – which aid in the absorption of fluid and carbohydrate, whilst also replacing electrolytes that are lost as a result of sweating. The combination of carbohydrate and electrolytes affects the concentration (or osmolality) of a drink. Isotonic drinks have an osmolality of between 270-330 mmol/l; those with an osmolality less than this are hypotonic solutions, whilst those with a higher concentration are hypertonic solutions. Drinks that are hypotonic will result in rapid fluid absorption, but limited energy replacement, whilst the high osmolality of hypertonic solutions may slow the process of emptying from the stomach into the gut and the transport of fluid from the gut to body tissues.