Over the last two decades one of the most popular forms of exercise in the health and fitness industry is core stability training. While the fad is slowly starting to die off a bit you can still go to many PT clinics or gyms and see people being told to pull their bellybutton in when doing exercises.
I’ll confess, as a former student and current friend of McGill’s, the whole core stability concept (particularly the TVA/MF focus) has been a big thorn in my side for many years.
So where did this start? Where did we go wrong? That’s what I will explain in this article.
Before we get started I’d like to provide a definition of stability as stability means different things according to different people. The term stability has many meanings attached to it including control of movement, balance, stiffness or absence of movement, or structural stability. Webster’s definition of stability is
“ 1: the quality, state, or degree of being stable: as
a : the strength to stand or endure : firmness
b : the property of a body that causes it when disturbed from a condition of equilibrium or steady motion to develop forces or moments that restore the original condition
c : resistance to chemical change or to physical disintegration”
ORIGINS OF CORE STABILITY – PANJABI
In the early 1990s a researcher named Panjabi first defined the concept of the neutral zone as “A region of intervertebral motion around the neutral posture where little resistance is offered by the passive spinal column1,2.”
Panjabi proposed that a smaller neutral zone meant a joint was more stable. Panjabi recognized 3 contributors to spinal stability….
- Active subsystem: Spinal muscles
- Passive subsystem: Spinal column
- Control subsystem: Neural1,2
THE RESEARCH FROM AUSTRALIA ON THE INNER CORE
In the mid to late 1990s Paul Hodges, Carolyn Richardson and other researchers compared people with and without low back pain (LBP) to see how fast their core muscles activate in response to various arm and leg movements. What they found was that the transverse abdominnis (TVA) and multifidus (MF) were slower to activate in people with LBP compared to people without LBP. No other muscles were activated differently between groups3.
These studies created the idea that there is an inner core consisting of TVA, MF and the pelvic floor that contracts independently of the outer core. TVA was thought to increase spinal stability through its attachment to the thoracolumbar fascia. Drawing in or abdominal hollowing co-contracts the TVA and MF and increases intra-abdominal pressure3.
A 1997 study by Peter O’Sullivan et al showed that core stability exercises improved outcomes in people with spondylolisthesis compared to GP care4. Hides et al showed that training the inner core decreased the risk of developing LBP5.
As such it became believed that TVA and MF issues cause LBP, that everyone with LBP needs core stability exercises and that the inner core muscles are the most important muscles in spinal stability and low back health. Boom!! A new trend is born. Core stability exercises are still the most prescribed intervention for LBP.
What people who quote the research tend to miss is that Hodges et al’s research was cross sectional. As such we can’t tell if core muscle delays are a cause or consequence of pain. Pain can affect muscle activity and prospective research hasn’t found an association between baseline TVA function and LBP development6.
In addition the average delay in muscle activation was 20-50 ms across studies which is negligible. Some researchers have questioned the legitimacy of measuring MF via surface EMG as there is potential for crosstalk from the erector spinae. In addition some research has shown activation delays in other core muscles in people with LBP7.
STUART MCGILL AND THE GLOBAL APPROACH
In 2003 McGill et al measured the role of each muscle in spine stability and found that each muscle contributed fairly equally to spinal stability across various tasks8. His research also showed that drawing in decreased the activity of the outer core muscles and as such removed many stabilizing muscles from the equation9.
By contrast bracing (or stiffening all of the muscles in your core) contracts all muscles and has been shown to increase TVA and MF activity, increase spinal stability, and increase ability to respond to perturbations when compared to drawing in9. A recent study found efficacy for bracing exercises in LBP10.
Side note: some studies that claim to use bracing actually use hollowing or drawing-in.
However, most tasks (including lifting up to 70 lbs) require 4-8% core muscle maximal voluntary contraction for sufficient spinal stability. This level of core muscle activity can be generated naturally and reflexively without bracing unless you have a spinal cord injury or other neurological condition9.
Bracing does increase compressive forces on the lumbar spine11 and as such it may be appropriate for higher load tasks (ie heavy strength training) but it is “overkill” for day to day tasks.
PAIN SCIENCE AND THE BIOPSYCHOSOCIAL APPROACH
Through the work of researchers such as Peter O’Sullivan, Kieran O’Sullivan and others we know of the link between psychosocial factors and LBP.
A myriad of psychosocial factors are associated with the transition from acute to chronic LBP including stress, anxiety, depression, hypervigilance, fear avoidance, kinesiophobia, and catastrophizing12,13.
Some studies have also shown that some people with chronic low back pain have hyperactivity of their core muscles. The notion that the lumbar spine is unstable may cause these maladaptive beliefs and behaviours and may cause more focus on protection of the spine12,13.
Studies in 2012 and 2014 have shown that core stability exercises were not superior to general exercise in improving outcomes14,15. One important thing to note is that the general exercise protocols in many studies often included general core exercises (ie planks, birddogs etc). A study in 2017 showed core stability exercises provided better outcomes at 3 months compared to general exercise but no measures were made at 6 & 12 months and a 2018 review showed that core stability exercises were more effective than general exercises 16,18.
A 2013 systematic review found no correlation between changes in TVA and MF activation and clinical outcomes in people with LBP6. A 2017 paper showed that spinal stability in people with back pain didn’t significantly change after performing a motor control program or a general exercise program17.
Core exercises by themselves are not necessarily evil – it just depends on how they’re marketed. If they’re used as a means of movement and exercise that’s tolerated by the individual (assuming they are well tolerated) than that’s OK. If you say “you need to get your core working to keep your spine stable” you are more than likely delivering a nocebo effect.
Drawing in in isolation (i.e. when lying on your back & lifting your legs/arms up) is OK but isn’t advisable when doing advanced core exercises, heavy lifting, or balance exercises.
To summarize this long article
- Core muscle activity can be altered in people with LBP but it’s relevance to spine stability and LBP is questionable
- The TVA and MF aren’t any more important to core stability than any other muscles
- Exercises designed to focus on the TVA and MF haven’t produced any more favourable outcomes in LBP than general exercise
- Doing draw-in exercises in isolation is OK but drawing in shouldn’t be used when doing advanced core exercises, lifting, or balance exercises
- Bracing is appropriate when extra stability is needed (ie lifting heavy loads) but shouldn’t be used for day to day tasks
- The belief that “your spine is unstable” may (in theory) cause issues like fear avoidance, hypervigilance and guarding which are associated with chronic LBP
This was originally posted on Eric Bowman’s website. You can click here to read more blogs from him.