Why Full Sit-ups Can Back-fire

Core training is the foundation of great athletic performance, whether you’re a seasoned pro or week-end warrior. The core consists of the lumbo-pelvic-hip complex, and the thoracic and cervical spine-not just “abs”. 29 muscles attach to this powerhouse allowing   efficient acceleration, deceleration, and stabilization during dynamic movement. The abdominal wall, part of the core, is like an anatomical corset which also includes the deep transversus abdominis, which are below your belly button, internal obliques, the lumbar multifidus, pelvic floor muscles and the diaphragm. In any athletic move, these muscles work together, like a large stable column, to fire quickly and efficiently. This core, the body’s stabilization system, is like a good foundation on a home: if it’s not built right, the house will have problems somewhere down the road. In the gym, for example, someone lying on a weight bench lifting a bar for a chest press might have their lower back several inches arched in the air, demonstrating an inefficient core. So there is some misunderstanding of what kind of ab exercises work best to keep your mid-section strong .The full sit-up, for example, can place devastating loads on your spine. Simply modifying the sit-up to a partial curl-up, with the head and shoulders lifting a few inches off the floor, would be better.

In a New York Times article last month, titled Core Myths, the belief that the core means only the abs was challenged, for there is no science behind the idea. Stuart McGill, a professor of spine biomechanics and chair of the Department of Kinesiology at the University of Waterloo in Canada, compares the spine to a fishing rod supported by muscular guy wires. If all the wires are tensed equally, as in the whole lumbo-pelvic –hip complex, the rod stays straight. A core exercise program should emphasize all the muscles that girdle the spine, not just the abs, to ensure balanced strength. In his lab, he’s demonstrated how an average sit-up can exceed the limit known to increase the risk of back injury in normal American workers. In fact, in 1991, the safety of the full sit-up test was deemed no longer recommended for school-aged children as a means to test their abs. Instead, the partial curl was recommended.        

The full sit-up is 3 muscle actions: neck flexion, spine flexion, and hip flexion. It’s important to be able to sit up, no doubt, but repeated sit-ups   can place hundreds of pounds of compression on the lumbar disks. Hooking or holding the feet down places even greater stresses to the low back. Ironically, the bent knee sit-up has been taught to minimize the action of the hip flexor in the sit-up, though it is not correct. The abs can only curl the trunk. The sit-up is a strong hip flexor exercise whether the knees are bent or straight.

 Instead of full sit-ups, research shows that although there is no ideal exercise for each individual, the traditional crunch, or many variations of a curl-up, with the head and shoulders lifting a few inches off the floor, holding briefly, is a good exercise to challenge the abdominal muscles while imposing a minimal load to the lumbar spine. Speed of movement has an impact also. In The Journal of Strength and Conditioning Research May 2008, curl-up speeds were shown to have a significant impact on spinal loads, and that the combination of slow and moderately controlled speeds  is generally recommended for health and fitness programs. In their opinion, at the competitive level, coaches can choose fast explosive trunk exercises, but to also aim for a more varied program that includes trunk endurance, strength and good motor patterns that ensure spinal stability.

McGill says that 3 exercises, done regularly, can provide a well-rounded core stability program: practice the curl-ups, learn how to do a side-plank (lie on your side and raise yourself in a straight line, and the “bird dog” (from all fours, hands and knees, you raise an alternate arm and leg level  for 4 or 6 seconds) .


 Connie Aronson is an ACSM Health & Fitness Specialist in Ketchum, Idaho

Printed in the Idaho Mountain Express August 28, 2009