Ans: If you are worried about losing muscle mass, that depends on your usage of the treadmill. If you are using the treadmill for extensive workouts, it might result in a little bit of muscle mass loss, but at the same time, you will also gain endurance as well as muscle mass at certain regions such as calves and thighs. However, if you only use the treadmill for warm-up before a heavyweight workout won’t make you lose muscle mass.