De Jure Fitness Slam Balls for Strength and Conditioning Slam balls are used for exactly what it sounds like--slamming them on the ground! Normal medicine balls or wall balls can't take that kind of abuse, but the Rep Slam Ball is designed to be thrown to the ground thousands of times without breaking. Grippe textured rubber shell, with sand inside for weight. These are perfect for Cross Training and HIIT workouts, where the slam ball is a staple of metabolic conditioning.