Tools / Sweat rate
Sweat rate
Stop guessing how much to drink. One scale, one session, two weigh-ins: you will know exactly how much you lose per hour, and how much to put back. The full science is here.
Why it matters
−2 % = −20 %
Losing 2 % of your body mass in water is enough to collapse your time to exhaustion at high intensity (down to −20 %) and to shave 3 to 5 % off raw power. Blood thickens, stroke volume drops, heart rate drifts: you pay more for the same effort.
Drink too much = rinse
The opposite exists too: drink plain water beyond your losses and your kidneys flush it out, taking your electrolytes with it. If you are peeing clear every 20 minutes, you are not hydrating. You are washing. Hence the 600–1000 mg/L sodium window.
1 kg lost ≈ 1 L of water · indicative