Friday, August 28, 2009

Why sit-ups can backfire


Core training is the foundation for great athletic performance, whether you're a seasoned pro or weekend warrior.

The core consists of the lumbo-pelvic-hip complex, and the thoracic and cervical spin—not just "abs." Twenty-nine 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. It 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 his or her 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 midsection strong. The full sit-up, for example, can place devastating loads on your spine. Modifying the sit-up to a partial curl-up, with the head and shoulders lifting a few inches off the floor, is better.

A New York Times article last month, titled "Core Myths," challenged the belief that the core means only the abs, for there is no science behind the idea. Stuart McGill, a professor of spine biomechanics and chairman 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, McGill has 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 three 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.

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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 on the lumbar spine. Speed of movement has an impact also. In the May 2008 Journal of Strength and Conditioning Research, curl-up speeds were shown to have a significant impact on spinal loads. A combination of slow and moderately controlled speeds is generally recommended for health and fitness programs. The article advised coaches at the competitive level to 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 three 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 do the "bird dog" (from all fours, hands and knees, you raise an alternate arm and leg level for four or six seconds).

Connie Aronson is a health and fitness specialist and personal trainer based in Ketchum.

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