When muscle thickness is measured using ultrasound after strength training, differences in thickness between the upper and lower parts of the biceps indicate localized muscle growth, not just temporary fluid buildup.

If you already lift weights, doing partial reps that fully stretch the muscle builds the exact same amount of muscle as doing full-range reps over two months. As long as you lift the same total weight and do the same number of sets, your muscles will grow at the same rate regardless of which style you pick.

Measuring thigh muscle thickness with ultrasound near the top and middle of the thigh is a good way to see if your muscles are growing from training—but measuring near the knee might not show it.

Doing bicep curls only halfway up (keeping the arm stretched) might make the lower part of your bicep grow a tiny bit more than doing full curls, but the difference is very small.

If you're already used to lifting weights, doing upper-body exercises for 8 weeks — whether you move your arms all the way or just partway — can grow your arm muscles about the same amount, as long as you go until you can't do another rep and do the same total work.

When young men who haven't trained before do either multi-joint exercises (like curls) or single-joint exercises (like bicep curls) for 10 weeks, their arm muscles grow by about the same amount - there's no meaningful difference between the two types of workouts.