Action 1: supine barbell arm flexion and extension. First of all, lie on your back on a flat bench, bend your knees with your legs and let your feet step on the ground to control the stability of your body. Hold the barbell with both hands directly above your body, the grip distance is shoulder width, the elbow is slightly bent, and then the posture of the big arm is fixed. The triceps brachii exerts force to bend the elbow joint and the forearm. When it reaches the apex, it shrinks properly and then returns to its original state. Action 2: The barbell bends. This movement can be regarded as the first movement in the training of stance variation. First of all, stand naturally, with your legs slightly apart, so that your feet are shoulder width apart, straighten your back and contract your abdominal core. Hold the barbell with both hands, palms up, let the arms tighten at both sides, and fix the posture of the big arm. Then the forearm bends upward, stops for a while at the apex, and then slowly recovers.