When rats lift weights with different numbers of reps, their muscles show the same early biological changes no matter if they do few or many reps—and those early changes don’t tell us which workout will make muscles grow bigger over time.

If rats lift weights slowly for longer periods, they grow less muscle than if they lift quickly or at a medium pace—even if the total effort is the same—because how fast they move matters for muscle growth.

When rats lift weights with quick, short reps, their leg muscles make more of the cellular machinery needed to grow bigger, compared to slow, long reps—and this might be why quick reps help muscles grow more.

When you lift weights, your muscles temporarily stop building protein, but right after you finish, they kick into high gear to repair and grow—this happens because key signaling molecules in your muscles get activated during recovery.

Your muscles don't grow while you're lifting weights—they grow later, while you rest, because your body uses that time to repair and build new muscle tissue after the workout stresses them.

Your muscles don't grow while you're lifting weights—they grow later, while you rest, because that's when your body repairs tiny tears and builds more muscle tissue using the energy and nutrients you've eaten.