Even if your muscles are low on stored sugar (glycogen), your body still builds muscle just as well after lifting weights, as long as you eat enough protein.

In rats, lifting weights for two weeks made their muscles build more protein even though the usual muscle-building signals in their bodies went down. This shows muscles can grow without needing those normal signals.

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.

Doing short bursts of intense exercise can help your muscles make more proteins, especially the ones in energy factories inside cells, but it doesn’t always make your muscles bigger if you only do it for less than six weeks.

When female athletes don't eat enough to cover both their workouts and basic body needs, their muscles stop building protein as well, which could make them weaker or slower to recover.

Lifting weights at a challenging level makes your muscles build more protein, and this boost happens just as much in arms or legs that are used to exercising as in ones that aren't.