When your muscles don’t have enough stored sugar (glycogen), you can’t sprint as fast or go as long during all-out efforts like cycling or running hard.

Even when eating almost no carbs after a race, athletes who’ve been on a high-fat, low-carb diet for months can still rebuild their muscle sugar stores just as well as those eating lots of carbs.

Even though the person gets much weaker during their 10th sprint compared to the first, their muscles aren’t producing more lactic acid — which is weird because their stress hormone (epinephrine) is high, and you’d expect lactic acid to rise. So something is shutting down the energy system that usually makes lactic acid.

After a short, super-hard workout, your muscles refill their energy stores way faster than after a long, slow one—even if you eat the same amount of carbs.

Even after a really tough weightlifting session, your muscles don’t run out of fuel fast enough to slow you down, and they can refill just fine even if you don’t eat carbs for a while.

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.