Stand with your feet more than shoulder-width apart, knees slightly bent, toes pointing forward. Raise arms to your sides at shoulder level, put hands in fists, and bend your elbows. Tighten your abs, and punch your right arm to the left so your rib cage twists; keep the abdominals tight as you return to the starting position. Avoid swinging your body throughout the move; keep your hips steady. Repeat on opposite side. Alternate punches for two minutes.