Movement: Start on all fours and pike your hips up so that your feet are on the ground, and your arms and legs are straight. Now simply lift one leg up so that your knee is at chest height. Quickly switch legs and repeat in a rhythmic fashion. It is critically important in this exercise to achieve range of motion in the hips and not to excessively flex the lumbar spine. Start with a slow pace and short strides and increase speed and stride length as you progress.
Repetitions: When both legs have come up to the chest, this counts as one repetition.
Instructions and effects for the Mountain Climbers exercise 
Movement in Sagittal Plane