Body Solid Seated Leg Extension & Supine Curl Machine GLCE365Leg extensions and leg curls are high priority exercises with trainers, bodybuilders, and coaches. These exercises define the front and back of the leg. They strengthen the knees, hamstrings, quadriceps, and glutes. They also serve to protect the knee and joints from stress and injury. Body Solid Leg Extension & Curl Machines are engineered with the user in mind. They adjust to fit your body comfortably and position you for optimum exercise posture.