Weights in the real world are rarely as compact or easy to handle as barbells and dumbbells. More often than not, you’re hauling an awkwardly-shaped sofa up four flights of stairs, or trying to fetch that steel cooler off the top shelf of your garage, or manhandling a 55-gallon drum of almond butter into your pickup truck. Those weights (and, therefore, your attempts to move them) are awkward and inefficient—and they challenge whole swathes of muscle groups that you don’t normally use together at the same time.
Fortunately, there’s an increasingly popular tool to help train for exactly that kind of motion. Slam balls are relatively soft, like traditional medicine balls, but they’re typically larger, and they handle like dead weight—no bounce, no elasticity. Plus, since they're usually filled with sand, their uneven weight distribution forces athletes to grapple with the unwieldy bulk as it shifts in their hands.
The slam ball “allows for exercises, ranges of motion, and movement speeds that one cannot obtain with traditional gym equipment like barbells, dumbbells, kettle bells, or machines,” says Marc Megna, C.S.C.S., co-owner and chief body architect at Anatomy at 1220 in Miami. “It can be an easy way to add resistance to exercises that are typically performed with just bodyweight.”
While modern fitness enthusiasts might have first encountered the heavy-duty slam ball at a niche gym, medicine balls are no novelties. Hippocrates supposedly tossed around stuffed animal skins to stay in shape. Persian wrestlers trained with sand-filled bladders 3,000 years ago. Medicine balls of 4 or 6 lbs. are even used to play “Hooverball,” a volleyball-like game developed in the early aughts for President Herbert Hoover. (It’s exactly the kind of sport that quickly fades, only to then become a CrossFit WOD 100 years later.)
Several companies make heavyweight medicine or slam balls, but Megna recommends Dynamax, which was founded in 1985 is more or less synonymous with vinyl slam balls. "They're easy to grip and very durable," Megna says. "We use them indoors and outdoors on our turf area. We find they last the longest."