For how we live.
For most people eating normally, added electrolytes do little, and plain water rehydrates fine for ordinary exercise. The clearest endurance danger is drinking too much — and the proven use is illness, not the gym.
FIFA gave every World Cup match a mandatory three-minute break and the ATP set its first WBGT thresholds. Physiologists who study cooling say three minutes in direct sun does little to core temperature.
A 2002 review went hunting for the origin of "8 x 8" and found nothing. Two decades later, isotope measurements in 5,604 people put daily water use anywhere from about 1 litre to about 6.
A review of 42 studies on South Africa's Comrades Marathon finds medical encounters at up to 20 per 1,000 starters — mostly dehydration and cramping, not the cardiac events that draw the most attention.
Play was suspended on outside courts on Saturday when the tournament's five-point Heat Stress Scale maxed out. A ball kid collapsed during a match the same day. The threshold is set on physiology, not air temperature.
Across 111 runners completing up to four trials each, two consumer devices tracked the direction of fluid loss reasonably well but missed the amount by 25% to 33% on average.
Seventy-two runners were sampled before and after the 2024 Boston Marathon. Every marker of kidney and intestinal injury rose, and staying hydrated did not change that.
Twenty adults sat for three hours at 39 °C with and without a fan, hydrated and not. Dehydrated, the fan raised heart rate and stopped feeling better, while sweat losses rose either way.