Medicine balls are old school — like, really old school — and some believe that Hippocrates created them for his patients to help them recover from injury. Today’s medicine balls are made of leather or vinyl and are filled with ballast of differing weights. They also come in reactive and nonreactive versions — some bounce back quickly and others hit the ground and stick.
“Medicine balls help develop explosive power and rotational trunk strength,” Roberts says. “They also train you to absorb and redirect force, improving athletic performance and allowing you to project that power in every plane of motion.”