Core stability
A vast amount of rubbish is spouted about core stability by those poorly trained and frankly pretty dim blokes you meet in gyms. The terms ‘core function’, ‘core strength’, and ‘core stability’ have become chants with no real understanding of what the terms mean – ask one of them to explain the difference between stability and strength and then which of the two is more important and see what a panic this creates. However, you will, every now and then, meet one of them who has a profound understanding of these concepts and, if this is the case, ‘bind them to you with hoops of steel’.
The guru on all of this is Prof Stuart McGill, whose lectures and books we have devoured, and I would argue that he is the leading researcher in the world on low back stability. He talks about the following:
The Unstable Spine
To explain how injuries occur to the low-back from such apparently easy tasks as bending over to pick a pencil up off the floor he uses the concept of the unstable spine. It is worth having in your mind the idea that bending over puts a fairly high load through your low-back; think of it as similar to lifting a plank up by the thin end. His spectacular and spectacularly painful research shows that these daily tasks can cause your spine to ‘buckle’ if the spine isn’t working well or is unstable. This buckling can lead to tissue irritation and injury. What causes this to happen is a momentary dip in neural activation of some of the deep intervetebral muscles, leading to a slight rotation in one of the spinal segments. His solution to this is to train the deep muscles to “stiffen the spine against buckling” and improve its stability.
The Stable Spine
The vertebral bodies have to be able to move and they are brilliantly made to rotate in the sagital, frontal and horizontal plane, as well move along the three axes of these planes. Of course all joints have an inherent ‘joint stiffness’ because of the bony architecture, passive joint capsules and surrounding ligaments. Additionally, the muscles are able to control stability of these joints by coordinated muscle coactiviation. So, for us the task of creating a stable spine is testing but the pattern is there and we are rarely working with nothing. The goal is to deliver ‘sufficient stability’ which directly relates to optimal stability and mobility with no compromise to the spine. This can be done with exercises that provide coactivation of the deep intrinsic spinal muscles and abdominal wall (transverse abdominis) muscles.
The Main Lumbar Spine Stabilizers
Prof McGill used deep intramuscular electrodes (told you it was painful – but he did do it on himself) to identify the functional roles of the significant spinal stabilizer muscles. He also produced some mathematical models of spinal muscular activity and some amazing computer models to find the key muscles. He suggests that the important intrinsic muscles of the spine include the multifidus, quadradus lumborum, longissimus, iliocostalis and the transverse abdominins. Some gym staff surprises there – no rectus abdominis there so the six-pack may only be for decoration.
The Low Back Training Program
From McGill’s research on low-back stability, the data suggest that the healthiest training for the spinal flexors involves muscular endurance not strength training. He adds that “the safest and mechanically most justifiable approach to enhancing lumbar stability through exercise entails a philosophical approach consistent with endurance, not strength; that ensures a neutral spine posture when under load (or more specifically avoids end range positions) and that encourages abdominal muscle co-contraction and bracing in a functional way.” Bracing can be understood as if the muscles are guy ropes for tent poles as it is a neurophysiological phenomenon involving co-contraction of the abdominal wall and deep intrinsic muscles of the spine in an effort to better stabilize the low back.
Flexion-Extension “Cat-Camel” Warm-up
He recommends beginning with about six flexion-extension cycles of the “cat-camel” exercise. But he adds that these are done as a mobility exercise to reduce any present stresses on the spine, not as a stretch. These are shown really well on:
http://www.ccohs.ca/oshanswers/psychosocial/backexercises.html
(and you can see the Prof’s fingerprints all over this one.)
Quadratus Lumborum Training
For quadratus lumborum training he recommends the horizontal isometric side bridge (stick that in Google images and you’ll see what we mean) which can be done from a knee supporting position on the floor or a more testing version which utilizes a feet supported version. Another advanced version that involves the maximal involvement of the quadratus lumborum and obliques, with co-contraction of the critical spine muscles and transverse abdominis, is the rolling side bridge.
Rectus Abdominis, Obliques, and Transverse Abdominis Training
Prof McGill states that there is no single abdominal exercise that effectively challenges all of the abdominal musculature. He recommends several versions of crunches for the rectus abdominis and obliques. Pleasingly, he suggests avoiding sit-ups (with bent or straight legs) due to the high psoas muscles activation and the compressive loads this causes in the low-back. Similarly, leg raises also cause a great deal of psoas muscles activation and lumbar spine compression.
Back Extensor Training
Front lying (prone) upper torso (or leg) lifts off the floor may not be wise for people with low-back pain as these may place to much load on the spine. In this exercise the lumbar spine pays a very high compression penalty to a hyperextended spine (approximately 4000 to 6000 N) which transfers load to the facet joints and crushes the interspinous ligament. This exercise is certainly contraindicated for anyone at risk of low-back injury or re-injury due to the high spine loads and the extended posture. In my opinion it should not be prescribed at all.
The alternative exercise Prof McGill recommends is the “Bird-Dog” exercise or sometimes in the UK ‘supermen’. This exercise adequately engages the longissimus, iliocostalis, and mutifidus muscles of the spine, with much less stress to the spinal segments. Again a great site for a few pictures is: http://www.ccohs.ca/oshanswers/psychosocial/backexercises.html
McGill, S. M. (2001). Low Back Stability: From Formal Description to Issues for Performance and Rehabilitation. Exercise and Sport Science Reviews. 29, 26-31