In Cincinnati, it’s easy to pick up a piece of prehistory. According to Glenn Storrs, a curator at the Cincinnati Museum Center, you can hardly find a rock in the area that isn’t full of fossils. But there’s something else you can get your hands on that will put you in touch with the ancient past, and it’s just as easy to find at Cincinnati gyms: the medicine ball."Someday,” former Olympic weightlifting coach Istvan Javorek told ESPN The Magazine, “we will discover drawings of two cavemen throwing a rock back and forth. As long as there have been athletes, there have been medicine balls."It's not an unlikely supposition—historical evidence suggests Persian soldiers trained with sand-filled leather sacks approximately 3,000 years ago, and Hippocrates prescribed heavy, padded balls for therapeutic use in ancient Greece. Since then, medicine balls of all shapes, sizes, and weights have made their way into the fitness regimens of military personnel, NFL football players, US presidents, and average citizens alike. Specialists recognize the medicine ball as one of the Four Horsemen of Fitness, in addition to the indian club, the weighted wand, and the dumbbell.Today, personal trainers in Cincinnati use medicine balls in a seemingly infinite variety of exercises, strengthening cores, chests, arms, and legs while boosting coordination and flexibility. Popular exercises include the Russian twist, which requires participants to hold and rotate the ball left and right while keeping core muscles tight. Another classic move? Squats, which call for exercisers to keep the ball at arm's length as they perform crouching movements. The movement hones strength and balance, the better to win at Wii games—or, in the prehistoric era, outrun lions.