Young guys need their natural testosterone to get the full muscle-building benefits from weightlifting — if their testosterone is blocked with drugs, their muscles don’t grow as much, even if they...

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.

Young men need normal testosterone levels to get the full muscle-building benefits from weight training — low testosterone blunts the body’s muscle-growth signals.

In trained young men, two different types of weight training—high-volume and high-load—result in the same rate of muscle protein synthesis after six weeks, meaning neither style leads to greater growth of muscle contractile proteins under these conditions.

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.

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.