Jennifer Aniston's yoga pro Mandy Ingber (her new DVD, Yogalosophy, is in stores) shares her plan
Step 4: Forearm Plank & Leg Lift (Shoulders, Arms, Abs, Legs)
Start in plank position. Bend elbows to rest forearms on floor with elbows below shoulders, hands clasped in a fist (as shown). Pressing back in to heels, raise left leg an inch off floor, flexing foot, and holding for 15 seconds. Return to plank pose. Switch sides; repeat.