For men who exercise regularly, doing both weight training and intense cardio together doesn't slow down muscle building compared to just weight training alone, even after 10 weeks of working out.

When young men lift weights to build muscle, their muscle-building process speeds up at first but slows down after 10 weeks, even if they keep increasing the difficulty.

After 10 weeks of working out, men who are already somewhat active don't build muscle as efficiently as before, and their bodies don't respond as strongly to exercise—this happens whether they're doing cardio or weight training.

Lifting weights at a challenging level makes your muscles build more protein, and this boost happens just as much in arms or legs that are used to exercising as in ones that aren't.

Your muscles make more protein when you start lifting weights, but after a few weeks, that boost fades — even if you keep lifting harder — no matter if you use heavy or light weights.

When young men who haven't trained before do one-arm exercises for eight weeks, their resting muscle building speed goes up by almost half in that arm, but the part that builds muscle fibers stays the same, showing different parts of muscle react differently to exercise.