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When it comes to the crunch

Published: 
Friday, October 2, 2015
Dirt Under the Nails

It’s probably one of the most common questions we get at Total Rehab regarding core strengthening and developing “ah six pack”…To crunch, or not to crunch?

The answer is much more complicated than a simple “yes” or “no.” It actually depends on quite a number of variables. Let’s deconstruct the crunch a little and see what it actually does to the body. 

To do a crunch, the person lies on his/her back with the knees bent and feet on the floor. The crunch is performed when the person lifts the head and upper body off the floor and then returns to the start position. It involves flexion, or bending, of the spine using the “six pack” muscles, scientifically known as the rectus abdominus, and is an activity that places moderate compression through the spine. It is usually done repetitively within a strength training program in sets of multiple repetitions.

There is a school of thought, supported by research on the spines of dead pigs (which are very similar to human spines), which states that spines can actually be seriously injured when subjected to repetitive bending. In the studies on pigs, the majority of discs in the spines either partially or completely herniated when subjected to repetitive cycles of flexion. This flexion with compression lends credence to the potential risks of doing a lot of sit-ups and crunches in the gym.

However, as with all research, there are significant limitations when it comes to generalising the findings to the human population. These studies were done on pig cadavers, without the presence of active muscle and all the physiological processes that are involved when we train our muscles and move our joints. Just as our muscles undergo processes that help them get stronger when we exercise, our bones and the discs of the spine do the same. The tissues of the body remodel, adapt and become stronger, which dead tissue cannot do. 

The studies on pigs also subjected the loaded spines to thousands of continuous bending cycles, which is far beyond what a normal strengthening program involves. In addition, when performing normal crunches in the gym, the bouts of crunches are done intermittently. This is important as it allows time for the tissues to remodel and recover from the stresses placed upon them during the sets of crunching. Exercise-induced disc herniations occur when failure from fatigue outpaces the rate of recovery. It is therefore extremely important that physical trainers and independent exercisers who enjoy the crunch do the exercise with the correct frequency and intensity to avoid injury. Provided this occurs, there is no real evidence to show that crunches are bad for the HEALTHY spine. 

So if crunches are not inherently dangerous to the healthy spine, does performing them convey any actual benefit, or are they simply a waste of time? Movement of the spine helps to lubricate the discs. Fluid moves in and out of the discs as we move about and bend and straighten the spine. Spinal flexion has been shown to encourage this. This movement of fluid actually provides nutrients to the discs and flushes waste products out, promoting healthier discs. This is important considering disc degeneration is linked to inadequate removal of waste products. 

In addition, crunches can help develop strength in the “six-pack” muscles and also help increase their size. For those athletes who require a lot of spinal flexion strength, the crunch may be a good exercise to perform. The crunch actually isolates the rectus abdominus quite well and may also be an integral exercise for those persons who enjoy the aesthetic appearance of the abdominal musculature, such as body builders and fitness enthusiasts. However, if one has a layer of fat over the muscles, then the six-pack would not be visible, despite it being very strong from repetitive crunching! 

Taking the above into account, it appears that crunches offer a favourable risk to reward ratio for those who have no spinal pathology. But there are some precautions and contraindications that should be considered when doing the crunch. 

This exercise should be avoided in anyone with any disc injury and in those who have an intolerance to the movement of flexion/bending. 

Technique is key, and one must avoid pulling on the neck, as this can cause neck injury. 

It is also extremely important to remember to allow recovery of the tissues stressed during flexion and not to overload the flexion movement in people who perform a lot of this movement throughout the day. Such populations include certain athletes and labourers who bend a lot, and people who sit a lot. Core strengthening for these people should involve other safer exercises that stimulate the core. So it is best to err on the side of caution and avoid the crunch. 

The crunch is not for everyone!

• Carla Rauseo, DPT, CSCS, ATRIC is a Doctor of Physical Therapy and a Certified Aquatic Therapy Rehabilitation Instructor at Total Rehabilitation Centre in San Juan. http://www.totalrehabtt.com

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