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 in a split stance with both of your hands up. Step 2 Stay light on your feet and shift from side to side as you throw uppercuts. Step 3 Alternate between both hands for the recommended number of reps or specific amount of time.