Image: Courtesy of the American Council on Exercise (ACE)
Do: Start on your hands and knees, with your knees directly under the hips and your hands beneath your shoulders. Brace your core. Point your left arm in front of you at the same time as you straighten the right leg behind you. Hold for eight seconds and then switch.
Don't: Matthews says that when people lift one leg, they often turn out that same hip. Engaging the core can help keep you level, and so can lifting the leg just to hip height.