If you have picked up a health, fitness or training magazine recently, you can not avoid reading about the importance of “core stability”. Core stability is touted as paramount to maintaining a healthy back, however the idea of what “core” actually means, what muscles are involved and what exercises are best vary greatly depending on who you talk to. When you think of the core, the abdominal muscles inevitably come to mind. But that is only part of the picture.
Many of today’s popular ideas of spinal stability originate from research out of the Australian physical therapy group back in the 1990s. The research showed that the transverse abdominis (TA), a deep abdominal wall muscle and the multifidus, a series of spinal muscles, thickest across the lowest part of the lumbar spine, had unique behavior when injured. The transverse abdominis was shown to have a feed forward ability, meaning it turned on before other muscles did during a task that required stability. 1,2. Further it was shown to have altered activity when there was a lower back injury, sometimes turning on late or not at all. The multifidus was shown to decrease in size and have increased fat content after injury local to the site of injury. 3 This deficit did not recover spontaneously, even if the pain went away and it was found specific exercise was needed to rehabilitate the area. 4 Therapists began to use very focused rehabilitative exercises to activate the multifidus and deep abdominal musculature.
The research became popularized, spilling over beyond physical therapy and other health disciplines to personal training and popular fitness culture. The rehabilitative concepts, while useful for addressing specific muscular deficits, grew beyond its scope shaping personal training and core conditioning programs. This may have led to an overemphasis of the deep musculature.
Researchers such as world renowned biomechanist Stuart McGill found that exercises used to activate many abdominal exercises particularly those that repetitively flex and extend the back, offer unhealthy loading of the spine and only work very specific muscles. Further he argues that emphasis on deep musculature can actually destabilize the spine (More on this next time). McGill’’s live and biomechanical modeling also showed that there are not necessarily muscles that were more important than others. All the muscles in the trunk are important at different times, with different loads, under different circustances.5 Movements in the body are almost never a result of one specific muscle, but a result of coordination of many muscles, or muscle systems. Muscles that are further away from the center of rotation (the spine) offer better mechanical advantage than deeper muscles. McGill’s approach is to take a broader stroke, training the movement, not an individual muscle. He developed exercises to address the trunk musculature more comprehensively, focusing on exercises that create adequate muscular challenge across a number of muscle systems while putting the least compressive load on the back.
These exercises are often distilled down to what is often referred to as the “Big Three”. (See the related article on our blog) These basic exercises are commonly used initially in lumbar spine rehabilitation. These exercises are also becoming popularized beyond clinical practice as well. (See the NY Times video here: http://video.nytimes.com/video/2009/06/17/magazine/1194841000095/core-values.html?scp=1&sq=core%20values&st=cse)
All patients are different and what is appropriate for one person may not be appropriate for another. But generally McGill’s basic spine sparing core exercises can be used across many patient populations. Clinically I typically pull from more than one school of thought. If there problems with joint mechanics or muscle adhesions, they are addressed with manipulative and soft tissue techniques. I may also look to identify overt muscular deficits such as multifidus or transverse abdominis issues. If present, muscular deficits are addressed and some basic motor control exercises are taught. However, I will usually progress quickly to include a broader and more balanced approach using various spine sparing exercises based on McGill’s research and concepts.
In our next newsletter, we will continue exploring spinal stability
References:
1. Cresswell, A.G, Thorstensson A. (1994) “Changes in intraabdominal pressure, trunk muscle activation and force during isokinetic lifting and lower. Eur J Appl Physio Occup Physiol. 68: 315-21
2. Hodges, P. W., Richardson C. A. (1997) “Feedforward contraction of transversus abdominis is not influenced by the direction of arm movement.” Experimental Brain Research 114 (2): 362-370
3. Hides, J.A., Stokes, M.J. et al. (1994) “Evidence of lumbar multifidus wasting ipsilatreal to symptoms in patients with acute/subacute low back pain.” Spine 19(2) 165-72
4. Hides, J.A. , Richardson, C.A. et al. (1996) “Multifidus recovery is not automatic after resolution of acute, first episode low back pain.” Spine 21(23): 2763-9
5. McGill 2. M, (2004) “Linking latest knowledge of injury mechanisms and spine function in the prevention of spine disorders.” J. Electromyogr Kinesiol 14(1):43-7
Mark Pitcher DC, Msc
chiropractor, exercise physiologist
