Hello, actually, for boys, running should be the best way to exercise, but running is very particular. If you run well, you can lose weight. If you don't run right, you will not lose weight, but you will get fatter and fatter. It takes at least 30 minutes to run, because the burning of fat starts after 30 minutes. After running, you need to relax your legs, otherwise they will become muscles, which is what I said just now.