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.
RECENT RESEARCH
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.
PRACTICAL IMPLICATIONS
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
References
1. Panjabi MM. The stabilizing system of
the spine. Part I. Function, dysfunction, adaptation, and enhancement. J
Spinal Disord. 1992;5(4):383-389; discussion 397.
http://www.ncbi.nlm.nih.gov/pubmed/1490034. Accessed September 27, 2017.
2. Panjabi MM. The stabilizing system of
the spine. Part II. Neutral zone and instability hypothesis. J Spinal Disord.
1992;5(4):390-396; discussion 397. http://www.ncbi.nlm.nih.gov/pubmed/1490035.
Accessed September 27, 2017.
3. Hodges PW. Is there a role for
transversus abdominis in lumbo-pelvic stability? Man Ther.
1999;4(2):74-86. doi:10.1054/math.1999.0169.
4. O’Sullivan PB, Phyty GD, Twomey LT,
Allison GT. Evaluation of specific stabilizing exercise in the treatment of
chronic low back pain with radiologic diagnosis of spondylolysis or
spondylolisthesis. Spine (Phila Pa 1976). 1997;22(24):2959-2967.
http://www.ncbi.nlm.nih.gov/pubmed/9431633. Accessed September 27, 2017.
5. Hides JA, Jull GA, Richardson CA.
Long-term effects of specific stabilizing exercises for first-episode low back
pain. Spine (Phila Pa 1976). 2001;26(11):E243-248.
http://www.ncbi.nlm.nih.gov/pubmed/11389408. Accessed May 27, 2017.
6. Wong AYL, Parent EC, Funabashi M,
Kawchuk GN. Do changes in transversus abdominis and lumbar multifidus during
conservative treatment explain changes in clinical outcomes related to
nonspecific low back pain? A systematic review. J Pain.
2014;15(4):377.e1-35. doi:10.1016/j.jpain.2013.10.008.
7. McGill S. Ultimate Back Fitness and
Performance (6th Edition-2017) - Backfitpro. 6th ed. BackFitPro Inc.; 2017.
http://www.backfitpro.com/books/ultimate-back-fitness-and-performance-6th-edition-2017/.
Accessed September 27, 2017.
8. McGill SM, Grenier S, Kavcic N,
Cholewicki J. Coordination of muscle activity to assure stability of the lumbar
spine. J Electromyogr Kinesiol. 2003;13(4):353-359.
http://www.ncbi.nlm.nih.gov/pubmed/12832165. Accessed September 27, 2017.
9. Grenier SG, McGill SM. Quantification
of lumbar stability by using 2 different abdominal activation strategies. Arch
Phys Med Rehabil. 2007;88(1):54-62. doi:10.1016/j.apmr.2006.10.014.
10. Aleksiev AR. Ten-Year Follow-up of
Strengthening Versus Flexibility Exercises With or Without Abdominal Bracing in
Recurrent Low Back Pain. Spine (Phila Pa 1976). 2014;39(13):997-1003.
doi:10.1097/BRS.0000000000000338.
11. McGill SM. Low Back Disorders: The
Scientific Foundation for Prevention and Rehabilitation. Champaign, IL:
Human Kinetics; 2002.
12. O’Sullivan P. Diagnosis and
classification of chronic low back pain disorders: Maladaptive movement and
motor control impairments as underlying mechanism. Man Ther.
2005;10(4):242-255. doi:10.1016/j.math.2005.07.001.
13. O’Sullivan P. Common misconceptions about
back pain in sport: Tiger Woods’ case brings five fundamental questions into
sharp focus. Br J Sports Med. 2015;49(14):905-907.
doi:10.1136/bjsports-2014-094542.
14. Wang X-Q, Zheng J-J, Yu Z-W, et al. A
Meta-Analysis of Core Stability Exercise versus General Exercise for Chronic
Low Back Pain. Eldabe S, ed. PLoS One. 2012;7(12):e52082.
doi:10.1371/journal.pone.0052082.
15. Smith BE, Littlewood C, May S. An update
of stabilisation exercises for low back pain: a systematic review with
meta-analysis. BMC Musculoskelet Disord. 2014;15(1):416. doi:10.1186/1471-2474-15-416.
16. Coulombe BJ, Games KE, Neil ER, Eberman
LE. Core Stability Exercise Versus General Exercise for Chronic Low Back Pain. J
Athl Train. 2017;52(1):71-72. doi:10.4085/1062-6050-51.11.16.
17. Shamsi M, Sarrafzadeh J, Jamshidi A,
Arjmand N, Ghezelbash F. Comparison of spinal stability following motor control
and general exercises in nonspecific chronic low back pain patients.
Clin
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18.
Gomes-Neto M, Lopes JM, Conceição CS, Araujo
A, Brasileiro A, Sousa C, Carvalho VO, Arcanjo FL. Stabilization
exercise compared to general exercises or manual therapy for the management of
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