Round 4: Crunch and Plank
The power in a punch doesn't come from the arm; it comes from the torque of twisting your hips and firing all that energy through the muscles in your core. Your obliques, abs, and lower back have to contract to throw (and absorb) punches, Foster says. While the twisting you do when throwing punches shadowboxing and hitting the heavy bag trains the obliques, the two exercises illustrated here strengthen the front and back of the core. Do them one after the other without resting, and then take a 60-second breather.
A) dumbbell crunch: Lie faceup, knees bent with feet planted on floor; hold a 10-pound dumbbell in each hand directly over chest, arms straight. Crunch up, keeping arms straight, until shoulder blades are off floor; slowly lower to starting position. Repeat for 12 reps.
B) Plank to failure: Hold a perfect forearm plank as long as you possibly can. (Aim for at least a minute; your goal is 2½ to 3 minutes.) Hips should be lifted and your back straight, with abs, quads, and glutes engaged, shoulders directly over elbows, and forearms parallel. Fix gaze six inches in front of you to keep neck neutral.