Your muscles store sugar (glycogen) to use as quick energy when you lift weights.

When you lift super heavy weights until you can't do another rep, your muscles use up a lot of their stored sugar (glycogen) to keep going — this shows your body is breaking down that sugar fast to power your workout.

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.

Lifting weights refills muscle energy slower than sprinting or HIIT, maybe because you don’t build up as much lactic acid and your muscles get more sore from stretching under load.

If untrained guys eat a high-fat diet for 7 weeks, their muscles use less stored sugar during medium-intensity exercise compared to eating a high-carb diet — it’s like saving their fuel — but their legs still take up the same amount of glucose from the blood.