HOW: Face away from an elevated surface. Place your hands on the ground directly under your shoulders and elbows locked out. Put your feet on the step with your toes pushing into the step creating a plank position. Straighten your knees by squeezing your quadriceps muscles. Hold that for a few seconds and repeat.
FEEL: You should feel your quadriceps muscle working as you straighten out your knees. You should feel a stretch when your knee is fully extended.