How many times you lift a weight affects what your body gets better at: lifting heavy weights a few times builds strength, lifting lighter weights many times builds endurance, and doing a middle amount builds muscle size.

When you lift weights, doing a few heavy reps makes you stronger, doing lots of light reps helps your stamina, and doing a medium amount builds bigger muscles.

If you mix up your workout reps—sometimes doing just a few, sometimes a bunch—your muscles grow about as much as if you always stuck to the usual 8 to 12 reps per set.

If you do the same total amount of lifting, whether you lift heavy weights for fewer reps or lighter weights for more reps, you'll build about the same amount of muscle as a beginner.

If you're lifting weights and go all the way to muscle failure, doing between about 6 and 35 reps per set can help you build muscle just as well as lower reps.