When you flex your limb, you decrease the angle between 2 bones. The knee, hip, elbow, and shoulder joints consist of flexion movements. When you bring your arm straight in front of you, you are flexing your shoulder joint. When bring your ankle closer to your buttocks and bend your knee, you are flexing the knee joint. This movement allows us to walk, run, and jump. It further allows the knee and other joints to absorb forces and stress placed on the body.