American College of Sports Medicine position stand. Exercise and fluid replacement

ACSM's position stand on fluid replacement gives guidance on staying appropriately hydrated during physical activity, across three phases: before, during and after.

Before exercise, the aim is to start well hydrated with normal electrolyte levels, drinking beverages along with normal meals when needed, at least several hours ahead so the body can absorb the fluid and urine output can return to normal. During exercise, the aim is to prevent losing more than 2% of body weight from water loss and to avoid large shifts in electrolytes, both of which can impair performance.

Because sweat rates and sweat composition vary widely, it recommends individualized plans, using body weight before and after exercise to estimate sweat rate. Drinks with electrolytes and carbohydrate can help more than water alone in some situations. Afterward, the goal is to replace any remaining fluid and electrolyte deficit, more aggressively when the deficit is large or recovery time is short.

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