Fitness left arm can't build muscles?
Originally, most people used the right arm as the main arm, which means that the right arm will exert more force unconsciously during exercise. This is a habit of people, but it is something that you don't usually notice, but after such a long time of exercise, the effect will be obvious. Therefore, I suggest you do more left arm exercises after each exercise. Nothing strange, hehe, don't worry, have a good exercise.