Gymnic Heavy Med 4 Soft Weighted Medicine Ball (20cm, 4 kg / 8.8 lbs.) The Heavy med balls represent an evolution of the classic medicine ball. Add resistance to a variety of different exercises to help strengthen core muscles. They are very popular in fitness and rehab. Filled exclusively with water, their surface allows a good grip. Thanks to the elasticity of the material, our Heavy med balls are safe to use on any kind of floor or surface.