Part I discussed why persistent pain can’t always be explained by “pain signals” from damage and degeneration.
Part II picked apart the idea that pain is perpetuated by poor posture and abnormal body structure.
If degeneration, posture, and structure aren’t good explanations for persistent pain, then maybe the problem isn’t mechanical – maybe our muscles aren’t working properly?
This time, let’s take a look at muscle imbalances and core instability – two similar ideas that are currently insanely popular in the fitness industry and physical therapy (my own profession).
Supposedly, muscle imbalances push and pull us in awkward ways, and weak core muscles cause spinal instability. Both of which are thought to cause persistent pain (if you’ve read part I and II, you may already see some problems with this).
What does science have to say?
The idea of strengthening weak and “long” muscles, and stretching supposedly short and “tight” muscles, is the basis of many therapists approach to pain problems.
On assessment, people are taken through a bunch of awkward poses and movements to determine muscle “balance” and postural symmetry. Similar looking exercises are then prescribed to correct any imbalances.
However, the scientific evidence that this strength / stretch method actually works to correct postural asymmetry is poor. 1, 2 It appears that correcting muscle imbalances doesn’t even straighten you up!
In fact, there is very little quality research on this topic, period. Personally, I couldn’t find any research to suggest muscle imbalance predicts acute or chronic pain. If good research is so hard to find, why is this idea so popular?
Furthermore, muscle imbalance may not be as important for injury prevention as once thought. One study on a group of elite football players actually revealed that their amount of muscle imbalance (as seen through MRI) had no relationship with their number of injuries! 3 And another study involving military personnel explained that targeted muscle strengthening does not reduce injury rates. 11 Picking the “right” muscles to exercise isn’t so useful after all.
How about the popular “core”?
Thought to be important in stabilizing your spine, the core muscles include the abdominals and the lower back muscles (some people include the muscles around your hips too).
Perhaps you’ve even heard the specific names of the “most important” muscles: the transverse abdominus, and the multifidus. These two are often the target of “core stability training” – exercises that are meant to strengthen these muscles specifically. Theoretically, this will stabilize your spine, prevent injury and decrease lower back pain.
It all started in the 90’s, with the observation that these muscles are functionally altered in people with low back pain (so yes, there was a little science behind it). 4 Almost over-night, programs were designed to correct these alterations, and therapists and trainers flocked to spend their money on learning how to better train the “core”.
But does this stuff actually work?
As mentioned above, just about any exercise helps pain, so early studies supported core training as effective. 5 However, these early studies didn’t compare this type of training to any other form of exercise. Studies have since revealed that these highly specialized exercises are no better than “general exercise” (like going for a brisk walk),6 and improvements in pain are not associated with improvements in core muscle function! 7, 8, 9, 10
Learning to stabilize the muscles of your core may be important for athletic abilities and heavy lifting, but as a treatment for chronic pain… not so much.
Cause or Consequence?
When someone in pain walks into a clinic, they may appear to have altered posture and function that looks like muscle imbalance or core instability. But how do you know this isn’t something new – caused by the injury?
There is research showing that muscle imbalance exists in people with pain (in terms of activation – not necessarily size and strength). 12, 13, 14 And as mentioned, there are alterations in trunk muscle activity with low back pain. 4
However, these studies usually look at people who are presently affected by pain. Since pain is known to cause muscle inhibition, 15, 16, 17, 18, 19 it’s just as likely we’re seeing a consequence of pain, not the cause. This inhibition can even occur at distant locations from the source of pain (e.g. back pain inhibits quads). 16, 19
It’s even possible that this muscle inhibition isn’t even a defect, but a defense – a protective response to prevent further injury and pain. Who knows?
Of course, including the core muscles and both sides of your body is still valuable in athletic training (which is a whole other topic). But we’re talking about pain here (especially persistent, chronic pain).
These ideas are often considered superior to those discussed in parts I and II because they are more proactive – involving exercise. Indeed, exercise is good for pain. But these theories unnecessarily complicate their prescription.
Exercise for people with pain, injury, or disease should be individualized to the person, taking into account their goals, and what their problems are (especially safety). It’s not a matter of finding the “right” muscles to exercise.
Where these ideas really fall short is in their underlying premise, which is not much different from the ideas discussed in the first two parts of this series. It assumes awkward forces cause “pain signals”, which is not exactly true (especially for chronic pain).
The next post will wrap-up these outdated theories with a discussion of why it’s important to let them go. The reason I’m writing these controversial articles is not just to be a contrarian, but because these unhelpful ideas can actually have negative effects.
Then, it’s finally time to start discussion how pain really works, with the first part of a new series: “How Pain Works”. Stay tuned!
Thanks for reading!
Speaking of controversy…. share and discuss! (rational arguments only please)
References will be posted as a comment below, in the following format:
6. van Middelkoop M, Rubinstein SM, Verhagen AP, Ostelo RW, Koes BW, & van Tulder MW (2010). Exercise therapy for chronic nonspecific low-back pain. Best practice & research. Clinical rheumatology, 24 (2), 193-204 PMID: 20227641