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...

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.

If you're trying to build upper-body muscle and you're already experienced with lifting, it's probably better to focus on the part of the exercise where your muscle is stretched, even if you don't do the full movement. Adding in the part where the muscle is more squished doesn't seem to help you grow more.

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.

Adding stretching between your weightlifting sets can help you build more muscle faster than just resting normally, without making your workouts take longer. Research suggests this method can lead to about 10.5% more muscle growth compared to 6.7% with regular rest over two months.