Core trunk strength is the key to most athletic moves yet the trunk is generally the weakest link. The 15 lb. GoFit Medicine Ball builds core trunk strength and joint integrity. All sports trainers now recognize core strength training as the logical starting point for an effective training program. Often athletes over-strengthen muscles at the expense of joint strength and no matter how strong your muscles are, you are only functionally as strong as your joints. You see this often in injuries to shoulders, elbows, hips, and knees. Medicine Ball training is designed to strengthen these areas and allows you to more fully access your muscle strength. * Before beginning any weight loss or exercise program, you should consult with your physician.