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When you place your hands on medicine balls (or basketballs!), the instability causes your core muscles to work 20 percent harder than when you do pushups on the floor, according to researchers in New Zealand. If you're worried about the balls rolling away—making you face-plant—start with the balls braced against a wall until you get more comfortable.
Try these pushup variations for a total-body workout.
Get more out of every rep with these spins on the super-effective move.
13 Simple Ways to Amp Up Your Pushup