Hydration Strategy During Exercise

The goal of an exercise hydration strategy (ACSM Position Stand) is to prevent excessive dehydration (>2% body-weight loss) while avoiding overdrinking.

Before: Arrive euhydrated. ACSM suggests drinking roughly 5–7 mL/kg (≈2–3 mL/lb) of fluid about 4 hours before exercise, topping up if urine is dark or absent.

During: Fluid losses of 2–4% of body weight can be tolerated, but performance suffers as dehydration grows. Aim to drink at a rate that approximates sweat rate, individualized by weighing before and after sessions (each pound/0.45 kg lost ≈ 16 oz/~480 mL of fluid). For exercise lasting over ~60 minutes, include carbohydrate (see endurance-fueling) and sodium ~0.5–0.7 g per liter to aid retention, palatability, and reduce hyponatremia risk (see hyponatremia). For efforts under an hour, plain water is usually sufficient.

After: To fully restore losses, drink about 1.25–1.5 L per kg of body weight lost (≈125–150%), because some fluid is lost as urine; include sodium (from fluids or food) to retain it. Rehydration is more effective spread over a few hours than gulped at once.

Sweat rates vary enormously (commonly 0.5–2.0 L/h, higher in heat); self-testing by weighing is the most reliable way to personalize intake. Heat acclimatization increases sweat rate but lowers sweat sodium (see exercise-in-heat).

• Keep dehydration under ~2% body-weight loss; avoid overdrinking.
• Pre: ~5–7 mL/kg ~4 h before exercise.
• During: match sweat rate (~0.5–2.0 L/h); >60 min add carbs + sodium ~0.5–0.7 g/L.
• Post: replace ~125–150% of weight lost (~1.25–1.5 L per kg lost) with sodium.
• Personalize via pre/post body-weight weighing.

• fluid-needs — baseline daily hydration.
• electrolytes / hyponatremia — sodium replacement and dilution risk.
• dehydration-performance — cost of falling behind.
• endurance-fueling — carbohydrate alongside fluid in long efforts.