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 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 strong and you train your back with either short or full movements on the lat pulldown machine for 8 weeks, you'll get just as much better at doing more reps with the same weight—no matter which style you pick.

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 untrained adult men lift weights twice a week for 8 weeks, doing 4-6 sets of 8-12 reps until they can't do any more, their upper arm muscles will get bigger - this is measurable with ultrasound or other imaging.

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.