17. Stay in control. Don't use momentum (for example, rocking your upper body back and forth) instead of your abs to do the work. Keep your middle muscles contracted throughout the entire range of motion. Let them pull your shoulders and/or hips off the floor. (July 1983)
18. Know when to take it easy. Your rectus abdominis, the large ab muscle, responds best to high-intensity training (doing tough exercises, not necessarily more reps). But if you hit it hard every day, the muscle will fatigue and you won't see results. Work your abs 2 or 3 times a week on nonconsecutive days. (Dec. 2003)
19. Add the bike to your ab routine. According to a study by the American Council on Exercise, the bicycle (lying faceup, bring right knee and left elbow toward each other, then switch sides) is the best waist-firming exercise because it uses every muscle in your abs. (Dec. 2001)
2006 Update Prefer normal crunches? Doing them on a stability ball is more effective than doing them on the floor because your abs (and core) will have to work harder to stabilize your position and you're able to move through a larger range of motion.
20 Fire 'em up. To engage the deepest muscles of your abs during any exercise -- or just sitting at your desk throughout the day -- try this: Inhale, then exhale and pull your bellybutton toward your spine, without hunching your shoulders forward --don't just suck in your belly. (Aug. 2004)