Proper alignment of the mountain climber is essential in order to properly work out the muscles involved during this exercise. In the plank position, make sure your hands are directly underneath your shoulders, shoulder-width apart. The feet are hip-width apart and your toes are curled under. Your legs and arms are straight. Your tailbone is tucked under and your abdominals are strongly contracted, keeping your back from hyperextending. Your chin is slightly tucked in, and there is a straight line from the crown of your head to your heels.
Once you are aligned in the plank position, draw your right knee into your chest by using your abdominal muscles. Do not let your right foot touch the floor. Do not let your shoulders move in front or behind your hands — keep them directly over your wrists. Extend your right leg back into plank position. Do not bob your hips. Maintain a straight line from heels to head. Repeat on the other side. To increase the cardiovascular effect of this exercise, increase the speed of your leg motion.