After a really tough workout, young guys lose about half a liter of fluid from outside their cells within a day — and it happens whether their energy stores are low or full, so fluid changes aren't just about fuel levels.

After a really tough workout, young guys lose a little bit of fluid from outside their cells — and it happens whether their energy stores are low or back to normal, so something other than fuel levels is affecting fluid changes.

When young guys burn off a lot of energy during intense cycling, their muscles lose stored fuel (glycogen), but this doesn’t seem to change how water is distributed in their arms, legs, or body — at least not enough for common body scanners to detect.

When male endurance athletes drink enough fluids to fully rehydrate after a long, sweaty workout, their muscles hold onto a lot more water than expected for the amount of fuel (glycogen) they're storing — about 17 parts water to 1 part fuel. This extra water isn't just stuck to the fuel; it might be due to temporary shifts in body fluids or increased hydration inside the muscles.

After intense cycling, young men burn through a lot of muscle fuel (glycogen), but that doesn’t change how water is split between cells and surrounding areas in their arms, trunk, or legs—measured by a common body scan method.

For male endurance athletes who are dehydrated after long workouts, drinking a little or a lot of fluid with carbs doesn’t make a difference in how fast their muscles refill energy stores in the first 4 hours after exercise.