MUSCLES ENGAGED Shoulders The shoulder is the most movable joint in the body. However, it is an unstable joint because of the range of motion allowed. This instability increases the likelihood of joint injury, often leading to a degenerative process in which tissues break down and no longer function well. Calves Calves (calf muscles) influence the ankles and contribute to overall ankle strength. Strengthening your calf muscles will help your balance and performing movements such as running, walking and jumping. Exercise Instructions Step 1 Start is a split stance with your hands up protecting your face. Step 2 Stay light on your toes and continuously punch with your left and right hand. Step 3 Punch straight in front of you and fully extend your arms with every punch.