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. Equipment Used Kettlebell The kettlebell is a cast-iron weight (resembling a cannonball with a handle) used to perform ballistic exercises that combine cardiovascular, strength and flexibility training. Sizes may range from 4 pounds (1.8 kg) to 175 pounds (79 kg). Exercise Instructions Step 1 Start in a standing position with your feet shoulder width apart while holding a kettlebell in one hand at your shoulder. Step 2 Keep your body tight as you press the kettlebell over your head. Step 3 Fully extend your elbow and lower the kettlebell back down with full control.