Weigh yourself before and after a typical session to measure sweat rate, or use an estimate. Then plan fluid and electrolytes for your next workout based on its length and how salty your sweat is.
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Losing more than 2% of body mass can reduce endurance and focus.
Drinking more than you sweat can dilute blood sodium (hyponatremia).
Replacing sodium on long or hot sessions helps you hold pace.
Sweat rates vary from under 0.5 to over 2 litres per hour depending on body size, fitness, intensity, temperature, humidity and clothing. Measuring your own rate in conditions like race day is far more accurate than a generic rule.
Sodium is the main electrolyte lost in sweat, with potassium a distant second (about 150-250 mg per litre). Sports drinks typically contain 400-800 mg sodium per litre; electrolyte tabs and salt capsules can top up for salty sweaters.
5-7 mL per kg body weight 2-4 hours before.
Replace about 70% of sweat losses; keep loss under 2%.
1.25-1.5 L per kg still lost, with sodium.
Weigh yourself nude and dry before a one-hour session, track how much you drink, and weigh again after towelling off. Sweat loss = weight lost + fluid drunk - any urine. Divide by hours of exercise.
Enough to keep body mass loss under about 2%, but never so much that you gain weight. Replacing roughly 60 to 80% of sweat losses suits most people.
Typically 500 to 1,500 mg per litre, with an average near 900-1,000 mg. If your kit has white salt marks or sweat stings your eyes, you are probably a salty sweater.
For sessions over about 60 to 90 minutes, in heat, or when sweat losses are large. Shorter sessions usually need water only.
Drink about 1.25 to 1.5 litres for every kilogram still lost, over the next few hours, with some sodium to help you retain it.
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