"Sit-ups till an album side was through ... broomstick twists until my balance betrayed me ... passing plates from partner to partner like a medicine ball until vertigo sabotaged my set ... hanging sit-ups from a jungle gym until I fell on my head and nearly broke my neck."

You just read the introduction to "Confessions of an Abdominal Junkie," a magazine article I had an absolute blast writing for MuscleMag International more than 20 years ago. Citing it now does something far more important than establish my abdominal expertise (and exercise extremism); it exemplifies a commonly made mistake that you have quite possibly made.Increasing the number of repetitions to decrease the size of your waist.While you may effectively incorporate 25-to-50- or even 100-rep sets to warm up for weightlifting or to increase core-muscle endurance for activities such as marathon running, long-distance bicycling, or all-day hiking, there's no such thing as spot reduction.In other words, even 2000 reps per day won't whittle your waist away.What can shrink the size of your stomach, though, is a comprehensive plan that integrates aerobic exercise, anaerobic exercise, and a bit of human physiology called nutrient partitioning by reducing your overall amount of body fat. The plan works whether you are currently carrying an excess of 45, 25, or five pounds of it.So with sufficient time, sustained motivation, and frequent fine tuning of your diet, you could eliminate what rolls over your belt like an unwanted awning when you sit down - or suck your gut down to such a degree that your midsection muscles jump out like a jack-in-the box when you put a hand to an ear and flex them.For either to happen, however, you need to know the difference between aerobic and anaerobic exercise.For most, biking on a trail at 10 miles per hour is an aerobic activity, which means as you're pedaling you're processing oxygen. The processing of oxygen allows the pedaling to continue for a few minutes (if you're not in great shape) or for a few hours (if you are).For all but pros, biking on a velodrome at 30 miles per hour is an anaerobic activity, which means as you're pedaling you're unable to process oxygen. In fact, you may not even be able to reach that speed (if you're not in great shape) or hold it for more than a minute or two (even if you are).The effort is that intense.In short, the degree of intensity in combination with your fitness level is what makes the exercise aerobic or anaerobic - whether it's biking, walking, swimming, skiing, running, or even lifting weights. And the degree of exercise intensity that burns the most body fat is whatever degree allows you to expend the maximum amount of calories over the course of the workout.Consequently, if you're carrying 45 pounds of unwanted flab and not in great shape, easier and longer is far better than shorter and harder. Starting with three or four 15-minute, moderately paced walks per week may suit your needs.Building up to three or four 45-minute, fast paced walks may be your goal three months from the start.The time to do anaerobic work is in the weight room, but only after giving your muscles a few weeks to acclimate to it. After that, you want to lift weights heavy enough to make your major muscle groups, like your quadriceps, hamstrings, glutes, triceps, pecs, and lats, fail after eight to 10 reps. (Smaller muscle groups, like your abs, calves, and biceps, respond better when failure occurs after 12 to 15 reps.)Failure forces the muscles to adapt and grow. Bigger muscles mean more calories are burned, between 50 and 68 per day per pound of muscle.Calories that - if you eat properly - come from stored fat.Conspicuous by its absence so far is any reference to consuming fewer calories. You don't have to do that to lose body fat.Instead, you incorporate a bit of nutritional science known as nutrient partitioning and change the composition of your meals.If you eat more protein and complex carbohydrates and less simple carbohydrates and fats, your body naturally burns more and stores less fat. And if you do want to speed up the stomach-shrinking process by reducing the cals you consume, don't cut back on protein or complex carbs cals.Just cut out the junk.Finally, when you do exercises for the abs, keep the sets short and intense.An abs exercise easy to picture is called the seated broom twist. It's the one often used as a way to warmup for a weightlifting workout.To do a rep, you simply rest a broom handle against your neck, hold the ends with your hands, and rotate your torso one way as far as you can. To do a warmup set, you continue rotating your torso rhythmically.It's not that hard to reach 100 reps if you relax and picture windshield wipers working on a standard setting. Unfortunately, those 100 reps are not intense enough to either build muscle or burn many calories.But if you do only 15 reps where you forcefully exhale before every rep, squeeze your abs as hard as you can, and always maintain that maximum tension, you'll create the type of muscular overload that creates muscle mass.