Few exercises have as many working variations as the push-up. Any physical trainer will tell you that integrating medicine balls into the workout will not only create a tremendous challenge, but also deliver extensive results that involve more muscles than the standard push-up.

So perhaps you've worked in a medicine ball during your daily routine. Maybe two. Heck, maybe three. But if you want a challenge that will not only work your shoulders, back and chest, but also every bit of your core, you've got to try this:

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It's immensely difficult, but the challenge alone is what makes it enticing to try. Make sure to place both hands on the front two balls before lifting up your first foot. It can't hurt to have a "spotter" to hold the rear balls in place at first.

Another option is an isometric hold: Stop yourself mid-push-up and hold for 30 seconds. You'll feel your abs, obliques, shoulders, forearms and legs working immediately.

The man working it in the video like it's nothing is Travis Ross, who has a number of videos of routines that you can add to your workout to make it even more extensive and thorough.

And if that's not enough to challenge you, or you still feel like you need more ways to mix it up, check out these other workouts to satisfy your athletic appetite.

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