Practical Science on Movement and Pain
Practical Science on Movement and Pain
It is an article of faith among many mainstream experts that poor posture, lack of core strength, and/or structural abnormalities such as bulging discs are major causes of pain, especially back pain. A further assumption is that by working to correct such imbalances, through stretching or strengthening regimes, or surgery, the imbalances can be corrected and pain will decrease. It is probably fair to say that the majority of physical therapy and corrective exercise done in this country is based on exactly these assumptions. Although these ideas have a common sense appeal, there is significant evidence questioning this approach. Here’s a brief review of the conflicting evidence.*
The idea that bad posture causes pain, especially back pain, is ubiquitous. A google search for posture and pain shows 4 million hits and reveals many sites devoted exclusively to improving posture. With so many posture police on patrol, someone with chronic pain will almost certainly be advised sooner or later that bad posture is the cause. If you go to a physical therapist with low back pain and a big curve in your low back, you will almost certainly be told that you need to suck in your gut, squeeze your glutes, tuck your tail, tighten your abs, and strengthen your core. If you have upper back pain and a sunken chest, you will be told to pinch back your shoulder blades, strengthen your scapular retractors, stretch the chest, and raise the sternum. Before running off to do these exercises, let’s see what the studies have to say about the link between pain and posture.
In one study, researchers looked at the posture of teenagers and then tracked who developed back pain in adulthood. Teenagers with postural asymmetry, thoracic kyphosis (chest slumping) and lumbar lordosis (overly arched low lack) were no more likely to develop back pain than others with “better” posture.
Another study looked at increases in low back curve and pelvic angle due to pregnancy. The women with more postural distortion were no more likely to have back pain during the pregnancy. A systematic review of more than fifty four studies looking at the link between pain and the measurement of spinal curves found no good evidente of a correlation between posture and pain. Leg length inequality seems to have no effect on back pain unless it is more than 20 mm (the average leg length difference is 5.2 mm). Hamstring and psoas tightness do not predict back pain.
These results are particularly striking given that many studies have quite easily found other factors that correlate well with low back pain, such as exercise, job satisfaction, educational level, stress, and smoking. Although some studies have found a correlation between back pain and posture, it is important to remember the rule that correlation does not equal causation. It may be that the pain is causing the bad posture and not the other way around. This is a very likely possibility. People will patients will spontaneously adopt different postural strategies when injected with a painful solution. Big surprise!
Based on the above, there is little evidence to support the idea that we can explain pain in reference to posture or that we can cure pain by trying to change posture. For more articles on posture, click here.
Another common idea is that herniated discs or other degenerative changes revealed by an MRI are major causes of back pain. If you have back pain and get an MRI or x-ray that shows structural changes near the area of pain, such as a bulging or herniated disc, the doctor may conclude that the pain is due to what is seen on the MRI. The doc may even recommend surgery to correct the structural defects. However, numerous studies show that many types of structural abnormalities are poor predictors of pain.
In one famous study, MRIs were performed on subjects who did not have back pain. Fifty two percent of the subjects had at least one bulging disc or other MRI abnormality for which surgery is sometimes recommended. Given these findings, the authors stated that: “the discovery by MRI of bulges or protrusions in people with low back pain may frequently be coincidental.” In a similar study, MRIs on individuals who had never suffered from low back pain revealed that one third had a substantial spinal abnormality and 20% under the age of 60 had a herniated disc.
In a study of pain free hockey players, seventy percent were found to have abnormal pelvis or hip MRIs, and fifty four percent had labral tears. The author stated that “this study shows the limitations of depending too heavily on an MRI. A surgeon may see something in the image, but it isn’t causing a problem.”
In this study, researchers examined forty four volunteers, age 20-68, with no history of knee pain. Sixty percent showed abnormalities in at least three of the four regions of the knee, causing the authors to conclude that “meniscal degeneration or tears…are highly prevalent in asymptomatic individuals.”
Studies of active baseball pitchers or overhead athletes consistently demonstrate very large percentages (over seventy percent) of torn labrums and rotator cuffs.
These are all issues for which surgery is sometimes recommended.
This is not to say that herniated discs, torn labrums or other structural abnormalities cannot cause pain. Of course they can, and you would rather have less damage than more. But if a large percentage of pain free people have bulging discs, then how likely is it that a bulging disc is the cause of your back pain? If you look close enough at almost any joint in the body, you will find something wrong with it. Don’t assume that whatever shows up on the MRI is the source of your pain. For more on the poor correlation between MRI results and pain, click here.
The idea that good core strength is essential for a healthy back is another ubiquitous idea. If you go to a physical therapist with back pain and a midsection that is any less impressive than an Olympic gymnast, it is a mortal certainty you will be told to strengthen your core. What is the evidence that poor core strength causes pain or that core strength exercises reduce back pain?
Before reviewing the studies, it is first interesting to note that most of life requires only minimal activation of the core musculature. During walking, the rectus abdominis has an average activity of two percent of maximal voluntary contraction, and the external oblique operates at five percent. During standing, trunk flexors and extensors are estimated to fire at less than one percent. Add more than fifty pounds to the torso and they fire at three percent. During bending and lifting muscular activation is similarly low. Given that daily life seems to require so little core strength, perhaps it is not surprising that research interventions to increase core strength have little effect on pain.
For example, one study showed that core strengthening exercises for pain free persons identified as having a weak core do not reduce the future likelihood of back pain. Numerous studies have been performed to test whether core strength exercises reduce back pain. The thrust of these studies is clear – although these exercises can improve low back outcomes, it works no better than general exercise. The obvious conclusion is that if core strengthening has any benefit at all, it works only because of the generally beneficial effects of exercise (or as a placebo), not because the core is a special area of concern. In other words, despite what we are told over and over, the current evidence states that there is nothing magic about core strength as means to prevent or reduce back pain.
The above results are surprising and counterintuitive, and raise many questions such as: why do these approaches seem to work; how can so many people be wrong; and if these aren’t the true sources of pain, then what is?
*Most of the studies referenced in this article are from three excellent papers: The Myth of Core Stability by Eyal Lederman; The Fall of the Postural Structural Model in Manual and Physical Therapies by Eyal Lederman; and The Traditional Mechanistic Paradigm in the Teaching and Practice of Manual Therapy: Time for a Reality Check, by Frederic Wellens.