The main role of triceps brachii is to straighten the elbow joint, extend the shoulder joint, stabilize the joint and protect it. 1. Straighten the elbow joint: Triceps brachii is the source of strength when straightening the elbow joint, through the elbow extension the body can complete a series of activities such as supporting the upper body, throwing, etc., which is carried out through the contraction of the triceps brachii. 2. Posterior extension of shoulder joint: Triceps is attached to the outer and lower edge of the glenoid of scapula, which can play the role of posterior extension of the shoulder joint, which can make the person swing the arm better, and the shoulder joint can be extended to the posterior side. 3. Stabilizing the joint: the triceps is attached to the glenoid and ligaments, which can stabilize the joint. 4. Protective effect: there are blood vessels and nerves passing through the triceps, the triceps muscle provides sufficient protection for it. In the part of the triceps muscle that is slightly lower, there are radial nerves passing through the triceps, the triceps muscle can also provide sufficient soft tissue support for it to prevent radial nerve injury.