Oct 15 2011
Do you hate doing sit-ups or crunches? Then I have some good news for you. According to Stuart McGill, a professor of spine biomechanics at the University of Waterloo, you shouldn’t be doing them because they can be bad for your back. Sit-up and crunches create a lot of compressive force on the intervertebral discs in your lumbar spine. How much compressive force? As much as 3,350 newtons. If you’re not into the metric system, that more than 750 pounds of compression!
The U.S. National Institute for Occupational Safety and Health (NIOSH) recommends a limit of 3,400 newtons of compressive force to help protect your intervertebral discs. They acknowledge that even at that level up to 20% of the population might suffer a disc injury with repeated exposure.
How is it that an exercise that’s often recommended to strengthen your abdominals and protect your back turn out to be bad for your spine? Think about what a sit-up or crunch involves. You’re strongly contracting muscles that compress the spine while it’s in a flexed position. That’s the same type of exposure you would have if you were lifting something heavy from the floor by bending forward at the low back. That’s just the kind of thing we’re always telling people not to do.
You’re not off the hook for exercising though. It’s still important to maintain good core strength and endurance to help protect your back. What are some core exercises that won’t be so hard on your disks? Look for yoga and Pilates moves that you can do with your spine in neutral. Bridges, planks, “bird dogs”, and similar moves engage your core without requiring spinal flexion or really strong muscle contractions. And don’t worry about it if you aren’t seeing those “six-pack abs.” Genetics and body type have as much to do with having that “ripped” look as conditioning of the muscles does.