MUSCLES ENGAGED Hamstrings The hamstrings play a crucial role in many daily activities, such as, running, jumping, walking and cycling. Strengthening your hamstring muscles help to protect your knees from injury by absorbing the stress placed on the knee. Weak hamstrings can lead to knee injury. 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 Pull the kettlebell between your legs as you pitch your body forward at the hips. Step 2 Drive through your heels and powerfully extend your hips. Step 3 Pull you elbow up high keeping the kettlebell close to your body.