The friends with thin arms want to increase the circumference of their arms by exercising their muscles, they should first understand what muscles are present at the arms. The muscles of the arm are divided into two parts, front and back, the front has biceps, rostrum brachii and brachialis. In the back, there are mainly triceps and elbow muscles. To increase the dimension of the arm, these muscles should be exercised. Exercise should be planned, step-by-step and targeted under the guidance of a professional trainer, and should not be done blindly overnight. Exercise muscles usually first exercise the biceps, rostrum brachii, etc. of the forearm, and then the triceps and elbow muscles, respectively. At the same time should increase the intake of protein, the muscle gain of the arm will play a supporting effect.