Come into an all fours position on an exercise mat with your hands directly under your shoulders and your knees directly under your hips. Lift your knees so they hover a few inches off the floor. This is your start position. Maintaining a braced core and neutral spine, lift your left hand on the floor and reach across to tap your right shoulder. Return the left hand back to the floor and repeat the same movement with your right hand. Perform this alternating movement for the required number of reps (or time).