Here are 20 medicine ball exercises to work out the major muscle groups in the body. Included, are exercises that definitely work the core muscles, a few that work the arm muscles, and a few that work the leg muscles. While this is not specifically a activity in and of itself, these exercises can be part of a activity. Lighter weight medicine balls could be used for a warm-up. Medium weight medicine balls could be used to work on quickness and agility. Heavier weight medicine balls could be used to help build muscle strength.