Mountain Climber

Start in a high push-up position, hands under shoulders, body in a straight line.

Pull one knee quickly toward your chest while the other leg remains extended.

Switch legs in a running rhythm -- the faster, the more cardiorespiratory load.

Keep your hips low and stable -- don't let them rise up or move side to side.

Core remains active the entire time to protect the spine.

Slow down for more core focus, speed up for cardio and fat burning.