If you're already strength-trained and do upper-body workouts for 8 weeks, it doesn't matter much if you lift all the way up and down or just do part of the motion—your muscles grow and get stronger about the same either way.

If you're already strong and you train your arms using only the part of the movement where your muscles are stretched (like holding the bottom of a bicep curl), you'll build just as much arm muscle as if you did the full movement — the stretch alone seems to be all you need.

Doing partial-range weight exercises with a longer muscle stretch can build arm and thigh muscles just as well as doing full-range exercises, as long as you’ve been training for a while and do it for 12 weeks.

Using machines or bands that change how hard they feel as you move might make your muscles work more evenly during an exercise, but that doesn’t always mean you’ll grow bigger muscles faster than with regular weights—especially if you’re just starting out.

If you lift weights with either light weights and short breaks, or heavy weights and long breaks—but keep the total work the same—you’ll still build muscle in about 8 weeks. So, there’s more than one way to get stronger and bigger muscles.

Even if you don’t move through the full range, doing the exercise where your muscle is stretched the most (like halfway down in a squat) builds more muscle than doing it where the muscle is bunched up (like a shallow squat).