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Core Stability

Updated: Nov 16, 2020

By Dave Emond


I start this piece with some entertainment.



Before we begin our adventure into the world of spine stability, “weak cores”, and jelly doughnuts, I’d like to point out that this article was largely inspired by a paper written by Peter Stilwell in 2017 (1). This paper aims to generate a foundation for clinicians working with low back pain, as it investigates how truly complex back pain can be. Simply, distilling low back pain as a result of “weak” muscles is doing an injustice to its true complexity and to anyone experiencing it.


Common societal beliefs that the “core” is vital for low back health, and having a “weak core” holds a causal relationship with low back pain, are prevalent, not only among the general population, but also amongst healthcare practitioners (2). A qualitative study interviewing physiotherapists in regards to the importance of specific pilates exercises showed that 43% of participants agreed “core” weakness was a reason to perform specific exercises. Unfortunately, that’s not how the cookie (or should I say, spine) crumbles. If the problem and solution really was that simple, we likely wouldn’t be seeing the dramatic increase in low back pain related disability alongside rising healthcare utilization rates (3). Something isn’t adding up.


Let’s address where this idea originated. The buzz of “core stability” has been around for at least a handful of decades now, stemming from a burst in studies observing the activity of trunk muscles (abdominals and low back region) via surface EMG (electromyography) in those with and without low back pain. Some earlier studies looked at how the spine behaved outside of the human body, which offers some value, but doesn’t paint the entire picture (4).


Going back to the line echoed in clinics and gyms across the world: “I have a weak core”, let’s have a look at how much trunk muscle activity is needed for certain fundamental activities.


Muscle activation and spine stability


I preface this section by highlighting that surface EMG (electromyography) data has its limitations, and the conclusions can be commonly misinterpreted by readers. The topic of surface EMG is very complicated and I will pass the baton off to Greg Lehman to explain it better here (NAF Podcast). In short, surface EMG measures voltage changes occurring at the surface of a muscle, and can be affected by a large number of factors. This means that high or low measurements aren’t directly related to muscle activity or how much force a muscle is able to produce. Therefore, we do have to take these findings with a grain of salt (5).


So what have some of these studies involving surface EMG found? If we look at the work of White and McNair from 2002, we see that walking only requires 2% of the maximum voluntary contraction (MVC) of the rectus abdominis (abs), and 5% MVC of the external obliques (6).


Additionally, Cholewicki and Panjabi observed trunk muscle co-activation in healthy individuals when standing in a position termed the “neutral zone”. The neutral zone is a position postulated to have the least amount of spinal stiffness that is not related to muscle (7). They found that in a neutral standing position, EMG measurements showed an average of 1.7% MVC of the flexor and extensor muscles of the back, which increased to 2.9% MVC when adding an external load of 32kg (imagine holding a 32kg kettlebell). This percentage of MVC is not a tremendous measurement (7).


As mentioned earlier, these values aren’t necessarily indicative of exact muscle activation or force production (it could be more or less than those values), but they are quite low nonetheless. This leads us to the question: how “weak” does one need to become before they are unable to support their own spine with their muscles? How weak does one need to be before they start experiencing more pain? We don’t have the answers, but the current state of the evidence suggests we might be better suited to look in other directions.


Should we still try to increase muscle strength? It always depends on your goals. If your goal is to increase strength to stabilize your spine, then according to the biomechanical research, you already have enough strength to stabilize your spine.


Why would we need more “core stability”?


Biomechanists have looked at the relationship between movement, load and spine injury. This in turn has played a large role in the persistent beliefs that loading the spine through motion is bad. Biomechanical research has been cited to support the notion that core stability is important for injury risk reduction (performance and movement efficiency is another topic altogether).


Studies by Callaghan & McGill (8), Schollum (9), and Oxland (10) are examples of using a porcine spine model (pig spines/vertebrae) to observe injury rates and mechanisms with specific loading protocols. We will look at the first of these in more detail, as it is one of the more popular and highly cited articles.


The group took dissected pig vertebrae segments and loaded them into a machine that could control for compression and motion of the joint in question (8). A variety of compressive loads were used and the spinal segment was flexed and extended for up to 86,400 consecutive repetitions (8). The authors of this study concluded that the intervertebral disc was more likely to herniate with repeated flexion and extension when greater compressive loads were experienced.


A study by Veres et al. is worth mentioning for spine loading, as the authors found that disc injuries can occur in both flexed loading, but also in a neutral position (11). This might be a study that makes us question if stabilizing a spine in neutral helps reduce risk of injury.


As with any research, we must consider the limitations involved. The research described investigating spinal loads was performed in vitro, meaning outside the normal biological context. It is performed in a controlled setting, whereby a single vertebral motion segment undergoes repetitive loading without rest, and no longer has the full ability to adapt or repair within the body. Despite the circumstance of the Callaghan and McGill study having lower thresholds of spine compression, approximate ranges of 34,000-86,000 consecutive cycles of flexion and extension simply do not happen in the human body.


Can we control for a neutral spine?


So even if we consider the in vitro data we have at our disposal, can we successfully stabilize our low back during activities we do every day or within the gym?


It appears that during a controlled movement, such as a kettlebell swing, the lumbar spine can flex up to 26 degrees, yet still results in clinically unimportant spinal loads (12). Squats and deadlifts may result in approximately 60% and 80% of maximal spinal flexion respectively (13). In addition, work by Arjmand has also shown that despite conscious effort, trying to prevent rounding of the lumbar spine by creating a more stable position or arching the low back, we can still get lumbar flexion ranging from approximately 25 to 40 degrees (14).


For more details, I'd suggest reading this post by Greg Lehman here.


Is lifting with a rounded back safe?


A systematic review and meta-analysis by Saraceni and his colleagues found that the totality of evidence does not support increased risk in developing low back pain when lifting with a rounded back (15). It is important to consider context here, as one individual may be more perceptive of pain during a rounded lift. As such, we can try to modify day-to-day activities to mitigate this. This differs from the inherent risk of rounded lifting, as it does not seem to be supported as a large risk factor for developing injury or pain in the low back (15). We have also seen that disc fiber strain or pressure within a disc does not vary much when comparing a more rounded versus less rounded posture (16). Even if our earlier in vitro studies hold some ground, in a complex environment such as a living human, the risk of seeing disc injury while lifting with a round back may not be clear cut as we thought.


Is core stability training useful for back pain?


Sometimes maybe good, sometimes maybe shit.


If we are looking at chronic low back pain, trying to target specific parameters such as trunk extension strength, trunk flexion strength or back muscle endurance seems to be an exercise in futility. It appears there is little to no support for these outcomes as driving factors for someone’s improvement in pain relief (17).


Furthermore, we need to differentiate between short term and long term results. A study looked into the utility of an abdominal brace during daily activities in addition to a strengthening or flexibility program, in individuals with recurrent low back pain. They found that regardless of exercise type, people made similar improvements (18). In this specific study, the authors did see small positive improvements when using an abdominal brace, however no differences were observed in the long term (18).


More so, if we want to compare specific movement control-related exercise programs to general exercise, we see no difference in their long term effectiveness to improve disability and pain. Both treatment interventions show improved outcomes, neither better than the other. Just like abdominal braces though, specific movement control exercise programs showed a very slight advantage in the short term (post-treatment) when it comes to disability outcomes, but this advantage was lost afterwards (19).


If we want to generalize even further, when comparing a walking program to specific low back muscle exercises, we see no difference between the two interventions even if we compare trunk endurance tests (20).


Here's a final and important point. Brace yourself (only if you want, you really don’t have to, as per above). Core stabilization exercises are superior to any alternative treatment, in regards to long term pain and disability, IF the alternative treatment isn’t exercise (21). When compared to any form of exercise, there are no differences in improvements in pain or disability (21).


What does this all mean?


It means exercise is good, but doesn’t have to be specific, or anchored to the concept of stabilizing an already stable human spine. It simply needs to be tailored around the human being in front of you and what will get them enthusiastic about exercise. As stolen from Bronnie Thompson, we should be prescribing “meaningful movement”.


So let’s wrap this up and hit our main takeaways from all of this:


Core instability being a primary driver for low back pain and disability is a common societal belief that doesn’t seem to be supported in the scientific literature.


The our backs are inherently quite stable, and we don't require excessive muscle involvement for our spine to remain stable.


In vitro studies observing spinal injury mechanisms, although still useful and important, are often taken out of context and misinterpreted to imply spinal fragility.


Despite our beliefs that we can control our spine to remain rigid, it tends to move during most of the activities we do every day, whether we like it or not.


In the context of pain and injury, lifting with a rounded back is generally safe, as long as it is within your abilities and you allow your body to adapt over time.


Core stability training is not necessary for someone with low back pain, nor will it guarantee injury risk reduction. It is no better than general exercise including walking, but it can still be helpful. When and why can we use it?

  • It can be a simple entry point to exercise for someone with limited access to big spaces or equipment

  • It may help certain individuals with symptom modification in the short term

  • You enjoy it. Just like some folks like getting an arm pump, feel free to enjoy a back pump or that “feel good” ab soreness the next day

  • Exercise is good

Lastly, core stabilization exercises are an appropriate intervention if it fits the patient and we surround it with the right narrative. Unfortunately false narratives can feed societal beliefs of fragility and avoidance of activity, and are in no way helpful to the global burden of low back pain. We're simply giving someone an alternative or preferred way to move and load their spine to help with the management of their back pain.


References:


  1. Stilwell P, Harman K. Contemporary biopsychosocial exercise prescription for chronic low back pain: questioning core stability programs and considering context. The Journal of the Canadian Chiropractic Association. 2017 Mar;61(1):6.

  2. Cuddy P, Gaskell L. How do pilates trained physiotherapists utilize and value pilates exercise for MSK conditions? A qualitative study. Musculoskeletal Care. 2020 Apr 6.

  3. Deyo RA, Mirza SK, Turner JA, Martin BI. Overtreating chronic back pain: time to back off?. The Journal of the American Board of Family Medicine. 2009 Jan 1;22(1):62-8.

  4. Lederman E. The myth of core stability. Journal of bodywork and movement therapies. 2010 Jan 1;14(1):84-98.

  5. Vigotsky AD, Halperin I, Lehman GJ, Trajano GS, Vieira TM. Interpreting signal amplitudes in surface electromyography studies in sport and rehabilitation sciences. Frontiers in Physiology. 2018 Jan 4;8:985.

  6. White SG, McNair PJ. Abdominal and erector spinae muscle activity during gait: the use of cluster analysis to identify patterns of activity. Clinical biomechanics. 2002 Mar 1;17(3):177-84.

  7. Cholewicki J, Panjabi MM, Khachatryan A. Stabilizing function of trunk flexor-extensor muscles around a neutral spine posture. Spine. 1997 Oct 1;22(19):2207-12.

  8. Callaghan JP, McGill SM. Intervertebral disc herniation: studies on a porcine model exposed to highly repetitive flexion/extension motion with compressive force. Clinical Biomechanics. 2001 Jan 1;16(1):28-37.

  9. Schollum ML, Wade KR, Shan Z, Robertson PA, Thambyah A, Broom ND. The influence of concordant complex posture and loading rate on motion segment failure: a mechanical and microstructural investigation. Spine. 2018 Oct 1;43(19):E1116-26.

  10. Oxland TR, Panjabi MM, Southern EP, Duranceau JS. An anatomic basis for spinal instability: a porcine trauma model. Journal of Orthopaedic Research. 1991 May;9(3):452-62.

  11. Veres SP, Robertson PA, Broom ND. ISSLS prize winner: how loading rate influences disc failure mechanics: a microstructural assessment of internal disruption. Spine. 2010 Oct 1;35(21):1897-908.

  12. McGill SM, Marshall LW. Kettlebell swing, snatch, and bottoms-up carry: back and hip muscle activation, motion, and low back loads. The Journal of Strength & Conditioning Research. 2012 Jan 1;26(1):16-27.

  13. Edington C. Lumbar spine kinematics and kinetics during heavy barbell squat and deadlift variations (Doctoral dissertation, University of Saskatchewan Saskatoon). 2017.

  14. Arjmand N, Shirazi-Adl A. Biomechanics of changes in lumbar posture in static lifting. Spine. 2005 Dec 1;30(23):2637-48.

  15. Saraceni N, Kent P, Ng L, Campbell A, Straker L, O'Sullivan P. To flex or not to flex? is there a relationship between lumbar spine flexion during lifting and low back pain? A systematic review with meta-analysis. journal of orthopaedic & sports physical therapy. 2020 Mar;50(3):121-30.

  16. Khoddam-Khorasani P, Arjmand N, Shirazi-Adl A. Effect of changes in the lumbar posture in lifting on trunk muscle and spinal loads: A combined in vivo, musculoskeletal, and finite element model study. Journal of Biomechanics. 2020 Feb 29:109728.

  17. Steiger F, Wirth B, de Bruin ED, Mannion AF. Is a positive clinical outcome after exercise therapy for chronic non-specific low back pain contingent upon a corresponding improvement in the targeted aspect (s) of performance? A systematic review. European Spine Journal. 2012 Apr 1;21(4):575-98.

  18. Aleksiev AR. Ten-year follow-up of strengthening versus flexibility exercises with or without abdominal bracing in recurrent low back pain. Spine. 2014 Jun 1;39(13):997-1003.

  19. Saner J, Kool J, Sieben JM, Luomajoki H, Bastiaenen CH, de Bie RA. A tailored exercise program versus general exercise for a subgroup of patients with low back pain and movement control impairment: a randomised controlled trial with one-year follow-up. Manual therapy. 2015 Oct 1;20(5):672-9.

  20. Shnayderman I, Katz-Leurer M. An aerobic walking programme versus muscle strengthening programme for chronic low back pain: a randomized controlled trial. Clinical rehabilitation. 2013 Mar;27(3):207-14.

  21. Smith BE, Littlewood C, May S. An update of stabilisation exercises for low back pain: a systematic review with meta-analysis. BMC musculoskeletal disorders. 2014 Dec 1;15(1):416.