Best Ab Workout: Should You Do Sit-Ups?

Sit-ups may be excellent for developing the abdominal muscles, but they increase the risk of back injury.

Sit-ups have been the mainstay of abdominal exercise for more than 100 years. Most people who want great-looking abs do sit-ups – hundreds of them. Is this the best ab exercise? More importantly, are they safe? Maybe not – you could be training your abs at the expense of your back.

Research by Dr. Raymond Chong, an assistant professor of physical therapy at the Medical College of Georgia, examined muscle exertion during six types of sit-ups. He found that the old standby – bent-knee sit-ups with arms folded across the chest – is still the best exercise for developing the rectus abdominis, the long and wide abdominal muscle on the front of your torso.

If sit-ups work the abdominal muscles best, that should be the end of the controversy. We should buckle down and crank out those sit-ups – the more the better. Conventional wisdom suggests that sit-ups will build firm-looking abdominal muscles and develop core strength for doing everything better, from waxing the car to hitting a tennis ball.

It’s not that simple. In a series of elegant studies on the abdominal muscles and spine, Dr. Stuart McGill and colleagues from the University of Waterloo, in Canada, found that sit-ups put so much stress on the spine that we shouldn’t do them at all! Their work also suggests that the sit-up test is dangerous and is not a good measure of fitness, after all.

You can develop ripped abdominal muscles and have a healthy back at the same time. Good ab muscle strength contributes to good back health – if you do the exercises correctly. Do abdominal exercises improperly and you can cause back injuries that will never heal. Chronic back pain is a big price to pay, particularly since you could develop fit-looking abs doing other exercises.

The Great Sit-Up Controversy

The Medical College of Georgia issued a statement about research on sit-ups conducted by Dr. Chong and his students. The study used a technique called electromyography (EMG). EMG shows how much muscles work during specific exercises, such as sit-ups and curl-ups, by measuring the electrical activity of the muscles. Scientists place electrodes over a muscle belly and the harder the muscles work, the more electricity is measured on the EMG. By placing the EMG electrodes (pads that pick up the electrical signal in the muscles) on key muscle groups, the scientists can tell which exercises are best for building the abdominal muscles.

The researchers measured abdominal muscle activation during six types of sit-ups. Subjects did the exercises with arms folded across their chests and feet stabilized. The exercise ball was the kind found in any gym – soft, pliable and 70 centimeters in diameter. The muscle EMG signals were fed into a computer so the exact muscle activation of each sit-up could be measured and recorded. Sit-ups included:

• Partial sit-ups  (crunches) – lifting the shoulders about six inches from the floor, performed on the floor.

• Full sit-ups – rising to a full lateral position with knees bent at a 90-degree angle on the floor.

• Crunches using an exercise ball with no assistance.

• Full sit-ups using an exercise ball with no assistance.

• Crunches using a ball held steady by an assistant

• Full sit-ups using a ball held steady by an assistant.

You might think doing sit-ups on the ball would be hardest because of the unstable surface. Dr. Chong’s group found that the most strenuous sit-up was the full sit-up from the floor, which activated the abdomen, back, shoulders, hips and legs. The full sit-up using the ball unassisted was the second most strenuous. The least strenuous was crunches on the floor, followed by crunches using a ball with an assistant, crunches using a ball without an assistant and full sit-ups using a ball with an assistant. They found that while crunches require less effort and less strain on the hip and lower back than full sit-ups, crunches placed more stress on the neck. There is less strain on the neck when the body is vertical, such as during a full sit-up.

The Downside of Sit-Ups

Canada’s Dr. McGill is widely regarded as the leading expert in the world in spinal biomechanics and back pain. His extensive research on the spine has provided valuable information about how to develop the muscles of the abdomen, back, hips and legs and how to prevent back pain.

Dr. McGill said Dr. Chong’s research didn’t tell the whole story about sit-ups. “The problem with work like Dr. Chong’s is that they neglect the resultant spinal load when challenging muscle,” he said. “A sit-up causes spine loads above the NIOSH action limit in most people, so muscle activation is only half the story.” In other words, sit-ups may be excellent for developing the abdominal muscles, but they increase the risk of back injury.

The NIOSH is the National Institute of Occupational Safety and Health that sets limits for body stresses in the workplace. Dr. McGill’s research shows that stressing the back repeatedly lowers its tolerance to injury. The NIOSH set an upper limit of back compression at 3,300 Newtons (N). A Newton is a measure of force. One bent-knee sit-up creates 3,350 N, while straight-leg sit-ups create a whopping 3,506 N – greater than the maximum level set by the NIOSH for predicting back injuries. Curl-ups, on the other hand, created only 1,991N of spinal compression, and side-bridges (a great exercise for your obliques, the muscles on the sides of your abs) created 2,585 N.

Part of our pre-occupation with sit-ups comes from a misunderstanding of the role of the abdominal muscles in movement. The torso region needs stability to transmit forces between the upper and lower body. The main function of the rectus abdominis is not to shorten and flex the trunk. Rather, it is an important stabilizer and force transmitter. This is suggested by the structure of the muscle: Tendons break the muscle into four portions, which give the well-developed rectus a six-pack appearance. The muscle is designed to transmit stresses around the spine, which increases the efficiency of the obliques. Thus, the rectus abdominis is more important as a spinal stabilizer than as a major factor in trunk movement.

The abdominal muscles are important stabilizers that affect performance and well-being of the muscles of the upper body, lower body and spine. It’s better to build the abdominal muscles by making them stabilize the body during exercise. Using the exercise ball and whole-body exercises using medicine balls are terrific for building core strength.

Safe, Effective Exercises for Ab Muscles

The goal of your ab program is to have fit, attractive, functional muscles that support the spine and help prevent back pain. It’s true that doing sit-ups overloads the abs, but they also cause back injury. If you do enough traditional sit-ups (straight-leg or bent-knee), you will probably suffer a back injury. The message from scientific studies is clear:

Don’t Do Sit-Ups!

Your midsection exercise program should emphasize three exercises: curl-ups, side-bridges and bird-dogs. Curl-ups develop the rectus abdominis muscle (front of the abdomen). Side-bridges work the obliques (side of the abdomen) and the quadratus lumborum muscle, a deep muscle that helps stabilize the spine. Bird-dog exercises build the spinal extensor muscles. EMG studies from Dr. McGill’s laboratory show that these exercises best load their target muscles (i.e., curl-ups: rectus abdominis; side-bridges: obliques and quadratus lumborum; and bird-dogs: spinal extensors), while minimizing the load on the spine. Combined, these exercises build endurance and help shape the muscles in your mid-section, while preventing back problems.

Curl-Ups. Lie on your back on a mat with one knee bent and your foot flat, and the other leg straight on the floor. Curl-up to raise your head and shoulders slightly off the floor. The center of rotation should be at the mid back (thoracic vertebrae) to avoid excessive neck movement (cervical flexion). Raise your elbow slightly off the floor as well, to prevent prying the upper body through the shoulders. The exercise progresses by first pre-activating the rectus abdominis and then the obliques (the brace) so the challenge involves increased curling against the brace (not with more flexion). As more bracing is added, overlay deep breathing patterns to condition your ability to breathe while ensuring a stable spine. Eventually, place your hands lightly on your forehead (do not pull on your head). Never curl up as far as possible because it places too much bending stress on the spinal discs. Build up to four sets of 50 repetitions.

As you become more fit, do curl-ups on an exercise ball. Lie on your back on the ball until your thighs and torso are parallel with the floor. Cross your arms over your chest and contract your rectus abdominis, raising your torso to no more than 45 degrees. Increase the stress on your oblique muscles by moving your feet closer together. Emphasize the motion of the rectus abdominis rather than the shoulder and neck muscles. Build up to four sets of 50 repetitions.

Side-Bridges. This is the best exercise for your obliques and is wonderful for promoting spinal stability and preventing back pain. This is not a well-known exercise. However, EMG studies show it strengthens the obliques and quadratus lumborum muscles and helps stabilize the spine.

The technique: Lie on your side and support your body between your forearm and knee. As you increase fitness, move the support from your knees to your feet. Repeat on the other side. Hold position for 2 X 10 seconds. Build up to at least four to 10 sets of 30 seconds on each side of your body. You can also do this exercise on an exercise ball.

Bird-Dogs. This isn’t an ab exercise, but it builds fitness in your torso so that you get balance and stability in the area. Start on your hands and knees; simultaneously raise and straighten your right arm and left leg until they are in line with your spine. Hold for six to eight seconds. Do not raise either your arm or your leg above spine level. Return to the starting position and immediately repeat the movement with the left arm and right leg. Build up to four to 10 sets of 10-30 seconds on each side of the body.

How to Get Lean, Fit-Looking Abs

The key to developing lean, defined abdominal muscles is to minimize body fat and develop your abdominal muscles without stressing your spine. You can do ab exercises five hours a day and still have a fat stomach. Spot reducing doesn’t work; you can’t lose fat in a specific area through exercise alone. Rather, you have to lose body fat throughout your body. An important part of your ab program is to use more calories than you take in order to create a negative calorie balance. You can only achieve this through consistent, clean eating and regular exercise. For maximum fat loss, you should do high-intensity cardio (running, biking, etc.) for 60 minutes, preferably five to seven days a week.

References:

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Cordo PJ, VS Gurfinkel, et al. The sit-up: complex kinematics and muscle activity in voluntary axial movement. J Electromyogr Kinesiol, 13: 239-252, 2003.

Fahey, T. Basic Weight Training for Men and Women. New York: McGraw Hill, 2004. (5th edition)

Fahey T, Insel P and Roth W. Fit and Well. New York: McGraw Hill, 2003 (5th edition)

Green JP, SG Grenier and SM McGill. (2002) Low-back stiffness is altered with warm-up and bench rest: implications for athletes. Med Sci Sports Exerc, 34: 1076-1081.

McGill SM. Low back exercises: evidence for improving exercise regimens. Phys Ther, 78: 754-765, 1998.

McGill SM Low Back Disorders. Champaign, IL: Human Kinetics, 2002.

Medical College of Georgia. Research pinpoints variations in sit-up techniques. Press release, Aug. 15, 2003.

Shrier I, D Feldman, et al. Comparison between tests of fatigue and force for trunk flexion. Spine, 28: 1373-1378, 2003.

Suzuki J, R Tanaka, S, et al. Assessment of abdominal muscle contractility, strength, and fatigue. Am J Respir Crit Care Med, 159: 1052-1060, 1999.

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