HOW: Begin in a tall plank position with your hands on the ground underneath your shoulders, and your feet straight out from your hips with your toes pushing into the ground. From here, keep your back flat, core engaged, and bring one knee up towards your chest. When it is as far up as you can go, move it straight back from your hip keeping the foot off of the ground. Repeat this motion for the prescribed amount of reps.
FEEL: You should feel your core and shoulder muscles working to stabilize your body. You should also feel your hip muscles working when you bring your hip forwards and backwards.
COMPENSATION: Don’t arch your back when bringing your leg back and forth.