Body-Solid Leg Extension and Prone Leg Curl Machine - leg 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 and Prone Leg Curl Machine - engineered with the user in mind. They adjust to fit your body comfortably and position you for optimum exercise posture. Full commercial warranty. Weight plate post is 1 dia. Olympic Adapter Sleeve, weight plates, and collars optional.