Adding variety to push-ups
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Medicine balls, stability balls, basketballs and BOSUs can all be used to decrease stability, working more muscles. Pausing at the beginning, end or middle of a movement will make it even harder. Some research shows unstable surfaces may increase the activation of the muscles that stabilize the shoulders, but studies are inconclusive. Wobbly surfaces will, however, definitely increase trunk stabilization," Suprak said. And the chest can drop lower than normal if you're on three balls, so be cautious about going deeper, Olson said. "Basically, all your muscles are doing double duty; they're moving and stabilizing you, which can easily lead to injury."
Calderon, the pushup champ, sets up for medicine ball pushups by putting each hand on a ball. "Then it's one foot at a time until I'm stable," said Calderon, who is shooting for a new record: pushups using just two medicine balls.