Bring yourself to the ground and enter a high plank position with your hands directly under your shoulders and your legs extended directly behind you. This is your start position. Keeping your core braced and not letting your hips drop, bend your left arm at the elbow towards to the floor, followed by your right arm, until you are in a forearm plank position. The proceed to immediately reverse the motion to come back into a high plank position. Repeat the same sequence for the required number of reps (or time).