I mentioned in another blog entry that I thought that crunches are a crappy exercise. In this article (scroll down a bit to Endless Crunches For Fat Loss). I would like to explain to my followers the reasons for that statement. There are two main reasons that crunches, sit-ups and pretty much the majority of trunk flexion exercises are crap. First, repeated spinal flexion has been shown to cause disk herniation. Second, when most people perform crunches, they are exacerbating their kyphotic thoracic spine.
Let me begin by explaining to you what I mean by ‘trunk flexion.’ The trunk refers to the body aside from the appendages and head. So if you could imagine what you looked like with no head, arms or legs, that would be your trunk. Flexion is a bending action. Stand up with your arms fully extended at your sides, now bring your hand up towards your shoulders by bending your elbow. This is elbow flexion. Trunk flexion is the bending of your trunk.
Let’s briefly discuss how trunk flexion can cause disc herniation. The word disc refers to intervetebral disc. These discs are wedged between our vertebrae, allowing our spine to bend and rotate. A herniation occurs when parts of the disc are pushed out of their normal position. This can cause back pain, leg pain and weakness of the lower extremities. During a sit-up, our lumbar (lower) spine is repeatedly flexed, placing large amounts of compression on our discs. It is this repeated disc compression that can cause the disc contents to spill out of the disc causing the problems listed above. See this video for a look at how pig spines react to lumbar flexion.
Young people usually feel immune to injury. I will admit, that I too sometimes feel that way, even though this is obviously not true. According to Adams and Hutton (1985) disc herniations are more likely in younger individuals because younger people’s discs have a higher water content and more hydraulic behaviour. So young people are at an even greater risk of disc herniations than older folks.
Dr. Stuart McGill, the world-renowned back specialist, has concluded that our bodies only have a limited amount of flexion cycles before a disc herniation becomes imminent. He puts the number around 28,000. So keeping lumbar flexion to a minimum is very important for a healthy back.
Now let’s examine how these trunk flexion exercises can exacerbate kyphotic posture. Kyphotic posture is basically an excessive rounding of the upper back. Have a look at Quasimodo for a bad case of kyphosis. Now, traditional ab training shortens the rectus abdominus (RA). The RA originates at the pubis and inserts on a few of our ribs and the xiphoid process of the sternum. By shortening this muscle, the ribs get pulled down. Stand up and do the crunching motion so you can see your profile view in the mirror, your upper back is rounded right?
You may be thinking “if I can’t do any type of crunch, then what the hell am I supposed to do for my core?” Well, there is a simple solution for that. There are far too many texts and studies that have shown that the core needs to be trained more as a stabilizer. There are a few different movements that should be utilized in a core training program: leg flexion with neutral spine (ball jackknifes), anti-extension (bridges), anti-lateral flexion (unilateral farmers carry), and anti rotation (pallof presses). I stole the movements from above from Mike Robertson; he’s one smart guy. You can pick two different movements and put them in each training session for your core training. So your core training for day one may look like bridges and pallof presses, day two could be ball jackknife and unilateral farmers carry.
I hope I can convert someone to stop doing ‘traditional’ ab training and start training the core in a safe and effective manner. Trust me, it’s still hard, and you will gain strength in your core. It will carry over to your other lifts and increase performance for sports as well.
Adams, M.A., and Hutton, W.C., (1985) Gradual Disc Prolapse. Spine, 10: 524
McGill, S., (2007) Function Anatomy of the Lumbar Spine. Low Back Disorders: Evidence-Based Prevention and Rehabilitation.