I don’t like abdominal crunches. I don’t prescribe them, and don’t like the fact they are still widely prescribed. I think they are, for most people, a bad exercise. There are three major reasons why.
Firstly, injury risk.
When we perform lumbar flexion we are challenging the anterior convexity of the lumbar spine. This results in massive compressive loads placed upon the anterior of the vertebral bodies of the lumbar spine and vertebral discs. This is problematic as for one, the inner two thirds of our discs are not innervated by sensory receptors (pain, mechano etc) meaning that we have to purge our way through two thirds of a disc before we know about it, a message delivered in the form of intense pain. And two, end-plate fractures (cracking of the top of a vertebrae) is very hard to pick up on scans, and large, repetitive compressive loads can lead to end-plate fracture.
Secondly, the eccentric stretching of the paraspinal muscles during a crunch increases pressure on the thicker part of the lumbar-disc-wedge caused by the crunching action.
So we have a double whammy- massive compressive force placed upon the front and back of the spine that we are blissfully unaware of until BANG- ‘my back just went!’
The second major reason why I don’t like crunches is the non-functionality of them.
If you like crunches, you do ’em. It is your body, do a million of ’em if you want to. But as trainers we are doing crunches to someone else’s body.
How many crunches do we need to be able to do in day to day movements? Not too many. The role of the rectus abdominis (RA) the majority of the time is not trunk flexion, rather it is prevention of trunk extension. Rectus abdominis is actually an important postural muscle as it helps to maintain a congruency between the pelvis and the rib-cage, hence stabilising the lumbar spine (in conjunction with many other muscles).
Viewing RA as a trunk flexor is an example of text-book anatomy. This is how text-book anatomy works: Muscle attaches from here to here, when it shortens it pulls these two bones closer together. Therefore if we pull those two bones closer together, we strengthen that muscle. And the truth in that is indisputable.
The problem with that approach is that we are looking at the muscle in isolation of those that it works synergistically with in a real person and we are also not looking at it in the context of real-life demands.
Finally, a colleague of mine asked me recently if there was any hard data on crunches and resultant injury rates/risk.
I have searched somewhat briefly and found nothing, and the reason I believe is this. For that study to exist the design would have to basically state ‘that abdominal crunches will be prescribed to one group, with a control group not doing crunches. This is done to test whether crunches increase the likelihood of injury’. Try getting that study past an Ethics board!
He asked me this as he knows a trainer that asked for the proof as she was defensive of the facts that she has always done crunches, she loves them, her clients love them and will keep doing them unless some proof is produced (refer to my blog http://correctiveexerciseaustralia.com/personal-trainers/the-6-traits-of-great-health-professionals/if you want to know what I think of that attitude!!).
I responded with this: If you like crunches, you do ’em. It is your body, do a million of ’em if you want to. But as trainers we are doing crunches to someone else’s body. Someone who is paying you to take their saftey into consideration when you are training them. And for me, the risk of doing crunches with my clients is far greater than the potential rewards, and that is my point.Share this with others