A vast amount of rubbish is spouted about core stability. Typically this is from those poorly trained and, frankly, pretty dim blokes you often meet in gyms. For them, the terms ‘core function’, ‘core strength’ and ‘core stability’ have become chants with no real background understanding of what the terms mean. Ask one of them to explain the difference between stability and strength, and which of the two is more important and see the look of panic that crosses their faces. However, every now and then, you will meet one who has a profound understanding of these ideas and, if this is the case, bind them to you with hoops of steel.
The guru on all of this core stability stuff is the Canadian, Prof Stuart McGill. His lectures and books we have all devoured. I think he is the leading researcher in the world on low-back stability. This is the man:
In his books he talks about ‘The Unstable Spine’. In order to explain how most injuries occur in your low-back, often from such apparently easy tasks such as bending over to pick up a pencil, he uses the concept of the unstable spine. It is worth remembering that bending over puts a relatively high load through your low-back. Think of it as similar to trying to stop a balanced plank of wood, about the same size and shape to your upper body, from falling over but by only by holding one end. This may help in getting an idea of the sort of forces we are talking about.
Prof McGill’s spectacular, and spectacularly painful, research shows that these daily tasks can cause your spine to buckle if your spine is unstable. This buckling can lead to tissue injury. What causes this to happen is a momentary dip in your neural activation. This leads to loss of control in some of your deep intervetebral muscles, and a slight rotation in one of your spinal segments. This is what happens when you reach for the piece of paper and suddenly can’t move. His solution is to prevent this by training your deep muscles to stiffen the spine and protect it against buckling by improving its core stability.
The Stable Spine
Your vertebral bodies have to be able to move and they are brilliantly designed to rotate in the sagital (coming from your front through to behind you), frontal and horizontal planes. they can also move along the three axes of these planes. All of your joints have an inherent joint stiffness which is created by their bony architecture, by the joint capsules surrounding the joints and the local ligaments. Additionally, your muscles are able to control stability of these joints by coordinated muscle coactiviation. So, for us at C1, the task of creating a stable spine is the challenge however, all is not lost as good movement patterns are usually there and we are rarely working with nothing. Our goal is to deliver sufficient core stability, which directly relates to optimal stability and mobility, with no compromise to the spine.
This can be done with exercises that stimulate and train co-activation of your deep intrinsic spinal muscles as well as your abdominal wall 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 played by the significant spinal stabilizer muscles. He also produced some mathematical models of spinal muscular activity and some amazing computer models to find which were the key and how they were working. He suggests that the important intrinsic muscles of the spine are your multifidus, Quadradus lumborum, longissimus, iliocostalis and the Transverse abdominins. Some surprises for the gym staff there – no Rectus abdominis! So, the six-pack may only be for decoration and keeping your intestines in the right place.
From the Prof’s research on core stability, the data suggest that the healthiest training for your spinal muscles 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.”
The concept of bracing as the key to core stability can be understood better if the muscles are seen as guy ropes for a your spine, which can be imagined as a bent tent pole. Bracing is a neurophysiological phenomenon involving co-contraction of the abdominal wall and deep intrinsic muscles of the spine in an effort to stabilize your back. So, there are two things you must do:
- Cat and camels
Flexion-Extension ‘Cat and Camel’ Warm-up. He recommends beginning with about six flexion-extension cycles of the cat and camel exercise. But, he adds that these are done as a mobility exercise to reduce any present stresses in your spine, not as a stretch.
These are shown really well here
(and you can see the Prof’s fingerprints all over this excellent Canadian government website).
The Plank. Then move onto the plank or bridge. The forearm plank is the one, and is well demonstrated here.
Quadratus Lumborum Training. For Quadratus lumborum training he recommends the horizontal isometric side bridge (stick that in Google images or go to our favorite Canadian site here and and you will 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 which is also shown on the page.
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, again shown nicely on his page here.
What to avoid
Pleasingly, he suggests avoiding sit-ups (with bent or straight legs) due to the high psoas muscle activation and the impressive compression this causes in the low-back. Similarly, leg raises also cause a great deal of psoas muscles activation and lumbar spine compression and should be avoided by anyone with a low-back problem. So, with your gym bloke – no flutter kicks and no inclined sit-ups with weights on your chest – ever!
Back Extensor Training. Front lying (prone) upper torso (or leg) lifts off the floor may not be ‘wise’ if you have low-back pain. They place far too much load on the spine. In this exercise the hyperextended lumbar spine pays a very high compression penalty (approximately 4000 to 6000 N) which loads the facet joints and crushes the interspinous ligaments.
This exercise is contraindicated for anyone at risk of low-back injury or re-injury because of these 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 called supermen in the UK, again this is well demonstrated here. This exercise adequately engages all the muscles you need: longissimus, iliocostalis, and mutifidus muscles of the spine, with much less stress to the spinal segments.
McGill, S. M. (2001). Low Back Stability: From Formal Description to Issues for Performance and Rehabilitation. Exercise and Sport Science Reviews. 29, 26-31