You don't have to swim for long. It is recommended to swim 15 minutes or so. The resistance of water is hundreds of times faster than that of air, so you can't swim for long. Exercise Swimming can exercise the muscles of the whole body, but you can't swim for too long, and swimming is not conducive to gaining weight. If you want to gain weight, it is recommended to eat less and eat more meals. To exercise muscles, you need anaerobic exercise Z.