Sports drinks aimed at enhancing endurance performance lasting several hours need to contain ~20 mM salt (sodium chloride) and ~10% carbohydrate in the form of glucose polymers and fructose. The salt and carbohydrate offset the losses of these substances caused by exercise. They also accelerate the uptake of water. Glucose polymers are used instead of glucose to keep the total osmotically active solute concentration (tonicity or osmolarity) of the drink below that of body fluids, because higher concentrations reduce the rate of emptying of the stomach and reduce the rate of uptake of water in the small intestine.
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