When people who already work out regularly train more often, it might help them build more muscle. Since their muscles don't respond as strongly to each individual session, working out more frequently keeps their muscle-building processes active for longer periods.

Your muscles don’t make more protein faster when you lower weights slowly vs. lifting them up—so growth must come from rearranging what’s already there, not just making more.

When you first start lifting weights, your muscles get tiny tears — and the protein your body makes right after working out is mostly used to fix those tears, not to make your muscles bigger yet.

When people lift weights at a high effort level, their untrained muscles build more protein quickly, but their already-trained muscles don't get the same boost, even if they do more work.

When young women who are new to weight training do more sets and lifts, and eat at least 1.5 grams of protein per kilogram of body weight, they tend to gain more muscle than those who don’t get enough protein.

People who build the most muscle from weight training show increased activity in their muscle cells’ systems that rebuild proteins, use energy during exercise, and fix damaged proteins.