How Should Athletes Fuel Before and During Exercise?

Athletes should begin exercise well hydrated and consume enough carbohydrate beforehand to maximize carbohydrate availability. During prolonged exercise, they should replace carbohydrate, fluid and electrolytes at rates matched to the event, environment and individual athlete.

The Reasoning and Mechanism

Before exercise, carbohydrate helps replenish muscle glycogen and liver glycogen, while adequate fluid supports normal cardiovascular function and temperature regulation. A general pre-exercise target is $1\text{--}4\ \mathrm{g\,kg^{-1}}$ of carbohydrate consumed $1\text{--}4$ hours before exercise.

For example, a $70\ \mathrm{kg}$ athlete choosing $2\ \mathrm{g\,kg^{-1}}$ should consume:

$$70\ \mathrm{kg} \times 2\ \mathrm{g\,kg^{-1}} = 140\ \mathrm{g}$$

The meal should use familiar foods and may include moderate protein. Fat and fibre are often limited close to competition because they slow gastric emptying and may cause gastrointestinal discomfort.

During exercise, carbohydrate maintains blood glucose and supports carbohydrate oxidation. Requirements depend mainly on exercise duration and intensity.

Hydration should be individualized using sweat rate, exercise intensity, temperature and humidity. Sodium-containing drinks can help replace electrolyte losses during prolonged exercise, particularly in hot conditions or for athletes with high sweat rates.

A common misconception is that athletes should drink as much water as possible. Excessive fluid intake can cause exercise-associated hyponatraemia, so athletes should avoid gaining body mass through overdrinking during exercise.

IB Exam Technique

For A.2.2, explain the physiological purpose of each strategy rather than only listing recommendations. Link carbohydrate to glycogen and blood glucose, and link fluid and electrolytes to thermoregulation, cardiovascular function and health. Always recognize that fuelling is individualized according to duration, intensity, environment and gastrointestinal tolerance.