The mountain climber [1] is a classic ab exercise, and I love it because not only does it work your core, it also has a cardiovascular component to it. While I enjoy traditional mountain climbers, at some point they will begin to feel easy. If that's the case, and you're looking for ways to turn a stagnant ab routine into an intense workout, you've got to try this mountain climber progression.

I find that doing mountain climbers on a stability ball, or another unstable object like a BOSU [2], makes the movement twice as hard and even more effective. Before you start performing the actual exercise, you're already engageing your core muscles to prevent yourself from falling off the ball, and you have to maintain that core engagement throughout the entire set. If this sounds enticing and you're up for the challenge, grab a medium-size stability ball and continue reading.

Stability Ball Mountain Climbers

• Begin in a high plank with your hands resting on the top of a ball.
• With your core engaged, bring your right knee forward under your chest, with the toes just off the ground. Return to your high plank. Switch legs, bringing the left knee forward. This completes one rep.
• Complete 12 reps, alternating legs.

If you love that exercise here are few more ab-specific exercises you can do with a stability ball [3].