Dear Julie: In defense of the crunch
share with you and your staff how a decade or so of research is transforming our understanding of how we create a strong sturdy center that anchors all of our movements
As a father of two young girls (5 and 3) I really appreciated your views on healthy sports participation, concerns about body issues and the importance of fun in physical activity. Like you I am also a physiotherapist with a special interest in spine function. I am also a chiropractor, was a spine biomechanics researcher, I completed a MSc in Spine Biomechanics with one of the authors of the references you cited (Stu McGill), I have published a few papers on trunk muscle function (here, here and here) during a variety tasks and was initially very interested in doing research on the lowly and often derided abdominal crunch (here and here). I love talking about spine stability and how much of this actually old research (I don't think it's emerging, most has been around since the 90s) is applied to clinic or sport in ways that the research does not actually support. I am also a former recreational gymastics coach and regularly "threw back tucks" after two beers at parties well into my twenties.
The big issue you had with your coach was his use of the crunch in his conditioning program. This was the area where our views seemed to differ. I think at best the jury is still out on much of what you have said and at worst the scientific data does not actually support your beliefs.
NO! Don't make me do crunches!
I personally don't think any exercise is bad. It may be inappropriate at different times in a training cycle or there may be other exercises that are better for the specific goals of an athlete. But I rarely throw any movement under the bus. The data just isn't there for that. In this letter I was hoping to give my rationale to defend the crunch and to discuss some of arguments you and many others (I think I'm in the minority) had against it. In the next few paragraphs I will cite the most common arguments against the crunch and give a rebuttal.
Argument #1: "Overused abdominals result in bums tucking under and the lower spine flattening"
I noticed that there was actually no reference for this statement. I would suggest that is because the research that has investigated the idea that strength training a muscle causes it to plastically deform and become shorter at its resting length and then pull bones into different position is actually lacking. I've written on this previously and for a review you can look here showing how strength exercises do not significantly change posture. While this is a common idea it just doesn't happen. Anecdotally, you will probably see the opposite postures in gymnasts. The tend to anteriorly pelvic tilt despite all those crunches.
A dominant motion in gymnastics is extension hence the concern by some for gymnasts to develop Spondys. Further, by what mechanism would even 15 minutes of crunches daily overcome all of the other neutral spine or extended postures that a gymnast undergoes? While I recognize muscle "shortening" as a common belief, it is certainly not supported in the "10 years of emerging research". Rather, it dates back to outmoded views of function perpetuated in the 1950s by Kendal and Kendal that somehow persist to this day.
Argument #2: Flexing the spine compromises spinal function
Gymnasts flex their spines. The do this under load and they do it repeatedly. Take a look at the gymnast doing the front tuck and the one doing the release on the parallel bars. Kind of looks like a crunch.
Most athletic sports don't have rigid spines all the time. Gymnasts certainly train to have a "tight body" but they also move. The spine generates and prevents movement. In gymnastics we perform front tucks, back tucks, back handsprings, back fulls etc. There is an approximation between the ribcage and the pelvis in these movements, under high loading. It happens. Thus we should train it. I love planks (I've had to defend planking in the past) but they don't mimic all of the demands of gymnastics. That is the purpose of conditioning - an overload stimulus to prepare for the demands of the sport. And remember, a curl up is not just the rectus abominis. Both obliques can be activated more than 50% MVC and the transverse abdominis also turns on substantially more than any indrawing exercise.
You mentioned that the ideal spine stabilty occurs with the co-ordinated action of all muscles. This is true but in order to progressively overload a muscle group to ask it to adapt we have to train in a somewhat isolated manner. To achieve strength adapations we probably need the MVC values to exceed 60-70%. Curl up variations can do this. Imagine if we trained all of the of the muscles of the trunk together as a team exceeding 60-70% MVC. The compressive penalty would be massive as would the increase in IAP. The spine would be in neutral but you would still be loading it incredibly - far greater than what would occur in the simple crunch. I would even guess that our neuromuscular system would not even allow such high levels of loading to achieve a strength response (for example see here).
Bottom line: gymnasts flex their spines thus we should prepare them to flex their spines under load
Argument #3: There are better exercises than the crunch
Yup, that is a good argument. You suggest planks (just as the coach did) and go on to suggest cartwheels and handstands as being even better than the plank. I think arguing that there are better exercises for gymnastics based on specificity or effort level is a good argument but it does not mean crunches are evil. Gymnasts could do V-snaps, leg lowers, rockers or other things that mimic their demands. However, the lowly crunch is a good progression. As for the cartwheels and handstands, aren't the girls already doing this during the session? The point of a conditioning component is to overload and stress the system to create adaptations. We want to choose exercises that are often a greater challenge than the goal task (cartwheels and handstands).
Argument #4: Crunches are dangerous because of spinal compression and disc strain
Again, a gymnast will flex their spine during the sport. There is probably more compression and shear during their gymnastic activities than the crunch. The crunch prepares the body to tolerate this load. Crunches are rather innocous relative to other exercises and tasks. What is 3-4000 newtons of compression and some shear? Thats nothing. If they do an L-sit on the parallel bars that demand will exceed the crunch. Or a kip-up on the uneven bars.
If we use compression and shear loading as the arbiter of safe activity we should get our kids out of gymnastics. Most of those activities will exceed NIOSH's limits. You quote Stu's book but we should go back to his original papers in the 1990's and we can see how low the compressive and shear penalties a crunch has in respect to all the other tasks we routinely ask athletes to perform. I don't see spine flexion as all that evil. Bret Contreras wrote a nice review questioning whether spine flexion is all that bad. At the very least, it is a grey area. Hence, I tend to have an issue with absolutist advice knocking one exercise.
Argument #5: Crunches create abnormal intra-abdominal pressure
Most spine exercises that will train capacity or stability of the trunk under high loads will create an increase in pressure. This increased IAP creates stability. Again, if we train with smart progressions and protocols the trunk and the whole musculoskeletal system will adapt as it should. You wrote:
For the diaphragm this results in a change in breathing patterns, including breath holding, to meet stability challenges, and reduced respiratory capacity.These scenarios will create an issue for sustained respiratory support for endurance in athletics. The pelvic floor may not be able to match the excessive pressure from above, which can lead to incontinence
I'm not sure what the issue is here. If you are concerned with breath holding, have the kids breathe during a crunch. Breath holding is normal and certainly even beneficial in my opinion if you want to increase stability especially during a landing or a back tuck. And while respiratory capacity might decrease while you are doing a crunch it does not carry over into prolonged dysfunction. How would it? I don't even know what "sustained respiratory support for endurance in athletics" means or how it can possibly be compromised by a crunch.
As for the pelvic floor, maybe the crunch should be the least of our worries. I would hazard that the IAP will increase to a greater extent in all of the other more challenging activities that occur in the performance of gymastics. Is it the flexion coupled with a little increase of IAP that is so bad? No papers you cited and I doubt any research shows this. But again, I think it is a far reaching conclusion to suggest that crunches lead to urinary incontinence. The studies you cited certainly don't support this. The Sapsford study you cited tells me that the pelvic floor muscles have greater muscle activity during upright sitting. Super. So they have less activity when your spine flexed. Why is this a concern? The Biceps muscle functions better at midrange yet we still train the muscle through its full range. Same with every other movement in the body. Why is just the spine that we avoid ranges of movement that have less than optimal force production?
Random Argument #6: The crunch isn't functional.
I think this depends on your goal task and your beliefs behind exercise prescription. I think in some sports we flex our spines and that flexion creates movement and is necessary. Take a look at my golf mechanics e-book. You will see in the kinematics graphs that trunk flexion is one of the first movements to start the swing. Think of paddlers that flex their trunk under huge loads and force production.
We are not always in neutral during sport and activities of daily living. Should we not then train out of neutral? Maybe the crunch isn't the best way, maybe you can use cables, or throw medicine balls at the ground but you are still training flexion.
And now for some random thoughts...
The creation of Nocebo with all this catastrophizing
I get worried when we use a biomechanical rationale to warn against the normal movement of simply bending our spines under load. If you tell the coach the danger of spine flexing and he passes this onto the kids what are you putting in their head? Don't flex the spine? Again, the do this all the time. They learn to think their spine's are delicate rather than this robust, beautiful structure with an immense ability to adapt to the strains we place upon it. Now when told how dangerous the crunch is, they become hypervigilant and their threat detectors are ready to go off. Our biomechanical models of teaching people not to bend in the workplace has failed and we have more persistent pain and disability days than ever. Lets not do this in our impressionable young athletes.
I'm on board if people hate the crunch and think they can create a program that avoids crunching. We could maybe critique the coach for not having some variety or some exercises that better mimic the functional demands of the sport. But, where I think we can go too far is by saying is such absolutist terms that some exercise is completely off limits and that is supported by recent science. Its not supported - the evidence is not there for that absolute statement. Right now, its an opinion. I think coaches can still have science and evidence on their side for justifying the use of crunches. This, like most coaching, comes down to preferences and experience - there are many paths to achieving a performance goal.
I end this letter much as you ended yours. Please don't view this as an attack on you. And to quote "I would be more than happy to answer any question you or your staff (i.e. like minded colleagues) may have as you try to assimilate this information". If there is some information out there that I have not heard of please send it my way. I am open to changing my view. I don't get a nickel every time a kid does a crunch so they could be gone tomorrow if there is some actual strong evidence against their use.
1. Jeff Cubos wrote a piece on gymnastics and movement which I remember liking at the time and then completely forgot when I wrote this. Its worth a read: