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 one foot in front of the other with your hands up to protect your face. Step 2 Step forward with your front foot and extend a jab at the same time. Step 3 Stay light in your feet and repeat the combination for the recommended number of reps or specific amount of time.