When you lift weights, your muscles grow because of the physical pulling and stretching forces they feel—this is thought to be the main reason they get bigger.

We’re not sure if the soreness and tiny tears in your muscles after a tough workout actually help your muscles grow bigger—or if they’re just a side effect.

The total amount of work your muscles do when lifting weights — how hard and how long you push — decides how strong the muscle-building signals get turned on.

If you lift weights until your muscles can't do another rep, pushing fast on the way up and slowing down on the way back, it helps your muscles grow bigger.

When you lift weights, your muscles grow bigger mainly because of the physical tugging and stretching they feel — and scientists think a special protein team (filamin-C and BAG3) might be the muscle’s internal detector that tells the cell to start growing, but we still don’t fully understand how it works.

When healthy young men lift weights until they're too tired to continue, their muscles grow about the same amount in both their arms and legs, no matter how heavy the weights are.