BODY PART TARGETED: WAIST (ABS), BACK & CORE
Assume a modified push-up position with your elbows bent 90 degrees and both forearms resting on the floor. Position your elbows directly underneath your shoulders and look straight toward the floor. Your body should form a perfectly straight line from the crown of your head to your heels. Your feet are together with only the toes touching the floor.
Hold position as long as you can, concentrating on keeping your abdominal and low back muscles tightened to prevent bending at the hips. Once a 30-second hold becomes easy, make the plank more challenging by alternately lifting each foot off the floor or holding the position for an extended amount of time.