For top powerlifters, two types of weight training—one that restricts blood flow and one that doesn't—both leave fast-twitch muscle fibers the same size after training.

For people new to strength training, lifting light weights with restricted blood flow works just as well as lifting heavy weights for building muscle size over 6 weeks.

Even though muscles got bigger, the actual muscle fibers didn’t get thicker or change type—so the growth might be due to other factors like fluid or connective tissue.

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.

At first, your muscles might actually get a little smaller from this kind of training, but after doing it again later, they grow bigger than before — the growth just takes time to show up.

Lifting weights for three months makes the muscle fibers in young men's biceps get bigger — both the endurance-type and power-type fibers.