Eric Cressey's Medicine Ball Training Master Class Medicine balls are one of the most potent tools for developing power. They can be used in training outdoors, indoors, in limited space, and with groups of any size. However, although medicine balls are used often and by many coaches, most medicine ball programs are not set up to optimally get the most out of the tool and athlete. Most information on medicine balls are just a bunch of random exercises. There aren't any good medicine ball programs out there that show you exactly what to do and how to use them properly...until now.