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Hydration and Electrolytes for Exercise: The ACSM Guide
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Losing just 2% of your body weight in fluid can measurably reduce endurance and focus. The American College of Sports Medicine (ACSM) position stand on exercise and fluid replacement gives practical, evidence-based targets for before, during and after training. Here is how to put them into practice.
Before exercise
- Drink about 5–7 mL of fluid per kg of body weight at least 4 hours before exercise. For a 70 kg person that is roughly 350–500 mL.
- If you produce little urine or it is dark, add another 3–5 mL/kg about 2 hours before.
- The goal is to start well hydrated — not overloaded.
During exercise
- The aim is to limit body-mass loss to under 2%. Because sweat rates vary widely, the best approach is individual — weigh yourself before and after long sessions to learn your own sweat rate.
- For exercise lasting longer than 1 hour, include sodium at 0.5–0.7 g per litre of fluid. This improves taste, helps retain fluid, and lowers the risk of hyponatremia in people who drink a lot.
- For endurance beyond an hour, adding carbohydrate (around 30–60 g per hour) helps sustain performance.
- Do not force excessive amounts — drinking far more than you sweat can dangerously dilute blood sodium.
After exercise
- Normal meals and drinks restore hydration for most people over the following hours.
- If recovery time is short (under ~12 hours) and losses were large, drink 1.25–1.5 litres of fluid per kg of body weight lost, with some sodium, to replace the deficit fully.
Helpful products
- Electrolyte powder — a simple way to add sodium for sessions lasting over an hour.
- Insulated water bottle — keeps fluids cool and makes regular sipping easier.
This article summarises general scientific evidence and is not personal medical advice. If you have a heart, kidney or blood-pressure condition, talk to a qualified health professional about your fluid and sodium needs.
Source: American College of Sports Medicine Position Stand: Exercise and Fluid Replacement. Medicine & Science in Sports & Exercise.
