When people lift weights to build muscle, how much muscle they seem to gain depends on how you measure it—different ways of measuring show different results.

When people who already work out build muscle, they don’t get much bigger very fast, and the gains slow down over time—so to tell if one workout plan is better than another, you’d need to study a lot of people.

When people lift weights regularly, their muscles usually get about 5% bigger on average, no matter what kind of weight routine they follow.

Measuring thigh muscle thickness with ultrasound near the top and middle of the thigh is a good way to see if your muscles are growing from training—but measuring near the knee might not show it.

Doing strength exercises with your muscles stretched more or less doesn’t seem to make much difference in how much each part of the muscle grows — all parts grow about the same.

Most of the research on how much to lift and how often was done on young men who already train—so we don’t know if the same rules apply to women, older people, or beginners.