This is about how hard you push yourself during certain exercises. It says you might not need to go all-out to failure to build muscle in some fibers, because one study found that legs not pushed to failure kept their muscle size while legs pushed to failure actually lost a little muscle. So, how hard you try could change how your muscles react.

When people do light weightlifting with restricted blood flow, their slow-twitch muscles can grow as much or more than their fast-twitch muscles, which is different from heavy lifting where fast-twitch muscles usually grow more.

When adults do light weight training with restricted blood flow, their slow-twitch muscles grow as much or more than their fast-twitch muscles, which is different from heavy weight training where fast-twitch muscles usually grow more.

Using a special training method with lighter weights and restricted blood flow along with heavy lifting might help trained people build more muscle by growing certain muscle fibers better, but different studies have found different results.

If you're a young man who already lifts weights, doing workouts with either light weights (lots of reps) or heavy weights (fewer reps)—as long as you push yourself until you can't do another rep—will make your muscles grow just as much either way.

Whether you lift light weights or heavy weights until you can't do another rep, your slow-twitch muscle fibers in your thighs grow about the same amount — but we can't be sure because the results are too uncertain.