Consider the three basic physiques, called somatotypes, that largely determine how we look. People who are born with a relatively small number of muscle cells tend to have a linear appearance (ectomorphic physique), and encounter more difficulty in developing large muscles. People who inherit a relatively large number of fat cells generally have a round appearance (endomorphic physique), and experience more difficulty in developing defined muscles.

Individuals who are gifted with a relatively large number of muscle cells and a relatively small number of fat cells typically have a triangular appearance (mesomorphic physique), and are more likely to develop large and defined muscles. These are the same people who characteristically have wide shoulders, and narrow hips, as well as large torsos and small midsections. With appropriate training, mesomorphic men and women have the best chance to achieve chiseled abdominal muscles.

The same training program will enable all of us to improve our midsection strength and appearance, even if we don't develop the so-called six-pack set of abdominal muscles prominently displayed by bodybuilders. For most of us, a reasonably lean and tight midsection is an attainable goal that can be realized through proper nutrition and exercise.

Nutrition
The role of appropriate nutrition should not be underestimated with respect to reducing fat and slimming your waist area. In fact, a small decrease in your daily calorie consumption results in the use of stored fat to meet your daily energy requirements. For example, if you eat just 350 fewer calories on a daily basis, you will lose about a pound of fat every 10 days. Generally speaking, shifting from a typical American diet to a lower fat menu that emphasizes grains, vegetables, and fruit will cut at least that many calories from your daily food intake.

Exercise
Endurance exercise such as running, cycling, or stepping, is an excellent means for burning extra calories, as well as for improving cardiovascular fitness. Depending upon your training intensity, 30 minutes of these aerobic activities can burn between 250 and 450 calories. Assuming an average of 350 calories per half hour training session, every five hours of endurance exercise should result in a one-pound fat loss.

Strength training also uses a lot of energy during the exercise session, burning about 250 calories in a 30-minute circuit workout. A typical circuit workout involves 10 to 15 different strength exercises performed with brief rests between stations. However, unlike endurance exercise, strength training builds muscle that requires additional calories all day long for tissue maintenance. Every pound of new muscle resulting from the strength training program increases your resting metabolic rate by 35 to 50 calories per day.

Of course, strength training is the best activity for developing your abdominal muscles, so that you have something to show in your leaner midsection. Although some people have more muscle building potential than others, the following strength exercises best address the major midsection muscles.

• Machine Abdominal Curl: Performed properly, this exercise effectively isolates the front abdominal muscle (rectus abdominis), and permits a progressive increase in resistance to maximize strength development.
• Machine Rotary Torso: This exercise targets the oblique muscles on both sides of the midsection. Rotating your torso to the right uses the right internal and left external oblique muscles, and rotating your torso to the left uses the left internal and right external oblique muscles. The rectus abdominis muscle is also involved in both movements, making this an excellent exercise for overall midsection conditioning.

If you do not have access to resistance machines, I recommend a combination of bodyweight exercises performed with as little rest as possible between segments.

• Basic Trunk Curl: This is the standard abdominal exercise, and it works very well when performed in a slow and controlled manner. Place your hands loosely behind your head to maintain a neutral neck position, and slowly curl your upper back off the floor until your abdominal muscles are fully contracted. Each repetition should be completed in about six seconds (three seconds up and three seconds down), so that 10 reps require about one minute of continuous abdominal work.
• Reverse Trunk Curl: This more difficult movement is performed by keeping your upper back on the floor, bending your knees with your feet in the air, and slowly pressing your lower back into the floor. Like the basic trunk curl, 10 properly performed repetitions should take about 60 seconds for completion.
• Push-Pull: This is the most demanding exercise in the sequence, and involves the rectus abdominis, internal obliques, external obliques, and hip flexor muscles. Begin by doing a basic trunk curl and remaining in the top position. Lift both knees so that both feet are off the floor. Bring your left knee backwards and try to touch it with your right elbow as you extend your right leg forward. Reverse this procedure by bringing your right knee backward and trying to touch it with your left elbow as you extend your left leg forward. Alternate this push-pull, trunk twisting action at a slow movement speed for about one minute.

For best results, consider a combination of sensible diet, regular aerobic activity, major muscle group strength training, and specific abdominal exercises. While there is no guarantee that you will sculpt a spectacular six-pack, you should develop a slimmer and stronger midsection, as well as a high level of overall fitness and improved physical appearance.

Wayne L. Westcott, Ph.D., is fitness research director at the South Shore YMCA, and author of several books on fitness including Strength Training Past 50 and Building Strength and Stamina.