Flexion and extension of parallel bars: pectoral muscle, triceps muscle and deltoid muscle (toe) are the main muscles, and latissimus dorsi and trapezius muscle are also practiced. The general process is as follows: hold the parallel bars with both hands, support your arms on the parallel bars, hold your head up and hold your chest up, the trunk and upper limbs are perpendicular to the parallel bars, and your calves overlap your ankles after bending your knees. The elbow joint bends slowly and the shoulder joint flexes, so that the body gradually descends to the lowest position. Pause for a moment and raise your arms until they return to their original state. Action requirement: 1. Slow down slowly, as much as possible. 2. Don't shake your body at will and keep your balance. 3. Don't complete the action in the back and forth swing of your body. Different movements need to produce different exercise effects on the main chest muscles and triceps brachii. 1. Choice of grip distance: narrow grip stimulates triceps brachii and wide grip stimulates pectoral muscle. 2. The choice of upper body inclination angle (side view): the center of gravity is on the upper body of triceps brachii, and the body should be backward, so that the arm can complete the movement behind the body; Focus on chest muscles and lean forward. 3. Angle between the upper arm and the trunk (rear view): Focus on holding the triceps brachii straight, don't be splayed when you put it down, and keep your arms parallel; Focus on the pectoral muscles. When you lower the pectoral muscles, you can stretch them out.