How Muscle Fuel and Water Come Back After Exercise

When fit male runners exercise for a long time in hot weather, their muscles lose nearly half their fuel and over 10% of their water — showing that heat and hard effort together really drain both energy and hydration from muscles.

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.

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.

When male endurance athletes refill their muscle fuel after long workouts, each gram of that fuel comes back with at least 3 grams of water stuck to it — even if they're not drinking much.

When your muscles store glycogen, it holds onto water—about 3 to 4 grams of water for every gram of glycogen. If glycogen runs low, cells get less hydrated, and that makes creatine less effective at pulling water into cells.