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.

If you're already strength-trained, doing arm exercises with only part of the motion (like half-bicep curls) builds your arm muscles just as much as doing the full motion — and the data suggests there's probably no real difference between the two.

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 back with partial pull-downs that stretch the muscle at the bottom, you'll get just as strong at doing full pull-downs as someone who does full movements the whole time — meaning stretching the muscle really hard might be more important than moving through the full range.

If you're lifting weights and stretch your biceps and triceps really far—like at the bottom of a curl or overhead extension—you'll build muscle just as well as if you move all the way up and down, as long as you get that deep stretch.

Even the middle parts of your muscles grow more when you stretch them fully during workouts — it’s not just the ends that benefit from full range of motion.