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Seated Abdominal Machine Crunches |
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Written by Stephen E. Alway, PhD, FACSM
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Monday, 23 April 2007 |
Either you hate abdominal work, or you enjoy it. Few people sit on the fence on this one, but either way, most of us would like to have better "abs." Adding a few more sets of sit-ups is not the complete answer for producing those washboard six-packs, but neither is "poor genetics" a valid excuse for possessing soft rows of fat rather than razor sharp muscle. Furthermore, such excuses are usually self-fulfilling prophesies. The solution is perhaps obvious and relatively simple, and it will not take you endless hours surfing the Web to find the latest abdominal shaping gadget.
One of the first premises for improving abdominal shape is to increase your metabolic rate, both acutely (for a short time) and chronically (throughout the day). Usually your metabolic rate will be elevated for several hours after a workout, so regular workouts are a key to your acute metabolic success. In addition, those dreaded aerobics for 20-30 minutes a day would go a long way toward acutely increasing your metabolic rate both during and after training, by utilizing those fat calories, which are blanketing your muscles as energy sources.
However, your long-term success is rooted in increasing your total lean body mass, because even as you sitt at your computer, larger muscles will burn more calories chronically and continuously than small muscles. You also need to choose abdominal exercises that shorten, and therefore tighten, the fibers in this area, rather than exercises that excessively stretch the abdominal fibers. Seated abdominal crunches are one of those exercises that will help force and optimize abdominal contractions.
The Muscles
The rectus abdominis is easily recognized as a long strap-like muscle. Actually, it's really a series of short fibers stacked vertically on each other. The linea alba is a thin tendon-like line that creates a groove in the middle of the abdominal wall, so the rectus abdominis appears to have left and right halves. Usually, there are three additional rows of horizontally placed tendons running across the rectus abdominis. These make the abdominal "blocks" that provide the "six-pack" look on the abdominal wall. The fibers of the rectus abdominis are short, and only run from one horizontal tendinous insertion to the next. When the rectus abdominis is tensed, the short fibers bulge between the tendinous grooves, almost like small ropes or blocks. If both right and left halves of this muscle contract, the trunk is simply flexed forward so the head and chest move closer to the hips and legs (assuming a fixed pelvis). Although there's muscle activity in all the blocks during most abdominal exercises, the upper two rows preferentially contract and shorten the most when doing seated abdominal machine crunches.
Striations along the side of the torso created by the external oblique muscle are easily seen in people with five percent or less body fat. The external oblique runs from the lower ribs by small bundles of muscle fibers from lateral to medial, in the same direction that your fingers would point, if you were to put your hands in your pockets. As the external oblique moves more toward the center of your abdomen, it unites with other slips of muscle fibers to form a flat fan-shaped muscle that attaches to the iliac bones of the pelvis and hip structure, and also to the linea alba. When both left and rights sides of the external oblique muscles work together, they can flex the trunk and move the head toward the feet.
The internal oblique muscle sits just deep to the external oblique muscle. Even though it's not visible, its shape and function make important contributions to the overall abdominal network. It attaches on a thick connective tissue sheath in the lower back, called the thoracolumbar fascia, and forms the iliac bone of the hip. Its fibers run around the side of the trunk at right angles to the external oblique muscle, fanning out from their origins and running toward the head (superiorly). It attaches on the lowest three or four ribs, where they become continuous with the internal intercostal muscles (respiratory muscles of the rib cage). Similar to the external oblique muscle, the internal oblique flexes the trunk at the waist and moves the head toward the feet, if both left and right portions contract together.
Seated Abdominal Machine Crunches
This exercise will most effectively contract the upper two rows of the rectus abdominis, but the internal and external oblique muscles will also assist in the flexion of the trunk.
1. There are several good machines commercially available for this purpose, and a few bad ones. You should have a machine that allows you to adjust your seat height so the center of your hip joint is directly in line with the center of rotation of the lever on the machine. You should also be able to adjust the chest bar so you can move forward as far as possible (limited by contacting your thighs), but limit the excursion so you'll come back only to a vertical seated position with a 90-degree angle between your thighs and torso. The chest bar or chest pad should lie comfortably across the mid-pectoralis region of the upper chest. Begin in a seated position with your knees and hips flexed to 90 degrees.
2. Take a breath, then exhale as you push forward with your chest against the padded bar. Think about curling your shoulders and upper back so your chin moves toward your chest as your upper body is curling (or crunching) toward your thighs. Do not "explode" from the starting position, but move it forcibly and fully controlled.
3. Pause for about two to three seconds in the fully crunched position. Squeeze the abdominals and at the same time try to tilt the pelvis slightly forward and up to strongly activate the lower blocks on your abdominals (which otherwise will be underworked in this exercise).
4. Inhale as you slowly control the weight as it returns to the starting position. Stop just short of the starting position; then repeat the movement as you exhale and crunch forward. Never allow the weight to pull you past a position that has your torso perpendicular to your thighs when you are in the seated position. If this occurs, stop and adjust the excursion of the bar to prevent this from occurring on the next repetition.
Helpful Hints
This is definitely not an exercise that requires a full stretch in the extended position. If you force your back into extension to stretch the abdomen between repetitions, you'll stretch the abdominal fibers such that you end up with a muscle that protrudes when you are fully relaxed. Moreover, strengthening the abdominal muscles normally reduces the risk of lower back injury, but leaning backward (past the vertical position) would result in starting the next rep from a position in which the spine is extended. This creates a significant torque through the vertebrae of the lower back and opens this area to potential injury. If you have any back discomfort either in the up or down phase, stop the exercise and adjust the seat and/or bar positions. If this doesn't help, ask your gym owner to get a better seated crunch machine! Do not use excessively heavy weights (again to avoid unnecessary torque through the lower back). Use a resistance that is sufficient to make your abdominals feel like melting plastic blocks within 20 repetitions.
You should not hold your breath during any sit-up or crunch, since this increases intra-abdominal pressure and prevents the abdominal fibers from shortening as much (although it might feel easier to do a sit-up or crunch when holding your breath). If anything, it's good to either exhale as you are crunching forward, or even better, exhale before you do the contraction. Then concentrate on achieving a maximal shortening of the fibers during the exercise.
The machine crunch, or any similar exercise that prevents excessive lengthening of the anterior abdominal muscles during the exercise, is but one component of a complete abdominal program. Make no mistake; sharp abdominal ridges require turning the intensity level up another notch in both diet and exercise. A sloppy, high-fat and high-calorie diet might give you potential as a sumo wrestler, but will do very little for your bodybuilding or most other fitness and sport objectives. In addition, you may need to add 15-20 minutes of aerobic training four times a week to help meet your short-term and long-term goals.
These adjustments, together with intense, controlled rounds on the seated crunch machine, will be the first necessary steps toward abdominal success. Of course, nothing worthwhile or lasting comes easily or overnight. But, if you carefully set high standards and realistic goals and deadlines to achieve success, and you move your dream forward with determination, nothing can stop you. Get ready to un-shelf your new "six-pack" this summer.
References
1. Arokoski JP, Valta T, Airaksinen O, and Kankaanpaa M. Back and abdominal muscle function during stabilization exercises. Arch.Phys.Med.Rehabil. 82: 1089-1098, 2001.
2. Bayramoglu M, Akman MN, Kilinc S, Cetin N, Yavuz N, and Ozker R. Isokinetic measurement of trunk muscle strength in women with chronic low-back pain. Am.J.Phys.Med.Rehabil. 80: 650-655, 2001.
3. Bower A. Absolutely fabulous? The TV ads promise easy rock-hard abdominals, but studies show there's no such thing as a free six-pack. Time. 158: 54-55, 2001.
4. Lehman GJ and McGill SM. Spinal manipulation causes variable spine kinematic and trunk muscle electromyographic responses. Clin.Biomech.(Bristol., Avon.) 16: 293-299, 2001.
5. Moore KL, and Daley AF. Cinically Oriented Anatomy. Lippincott Williams & Williams, Baltimore, 4th Edition pp. 1999. 178-187.
6. Suleiman S and Johnston DE. The abdominal wall: an overlooked source of pain. Am.Fam.Physician 64: 431-438, 2001.
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