Low back pain: unfit? just not doing much? or something else

For as long as I’ve been working in pain management (and probably well before), I’ve heard patients being described as ‘deconditioned’. From what we know about the effects of staying in bed because of illness or injury, it makes sense to think that if a person does very little they will become unfit. Common sense really. And from this assumption an industry of gym programmes and fitness initiatives have been instituted as an integral part of back pain rehabilitation.

Now before my physiotherapy colleagues start to lynch me, I’m not saying that these programmes should be banished into outer darkness because ‘reactivation’ has been shown to be effective in the recovery from back pain – but maybe it’s effective for quite a different reason from the one usually given.

Verbunt, Smeets & Wittink, in this editorial from Pain conduct a review of the relationship between physical inactivity and deconditioning in people with non-specific chronic low back pain, and find scant evidence for the strength of this belief.  Ooops.

There are several theoretical models that integrate the hypothesis that deconditioning is part of, and complicates, the recovery of people with chronic low back pain. The most popular in recent years is the pain-related anxiety and avoidance model (Vlaeyen and colleagues), in which people misinterpret their pain as threatening or something to be avoided at all cost, consequently fear moving, stop doing normal activities of daily living, and become deconditioned.  The model has been incredibly helpful for initiating a graded exposure approach to feared movements, and for shifting the psychological focus from low mood and into anxiety about pain and consequent behaviours.  BUT, as this review points out, it’s unclear whether being inactive and deconditioned maintain the ongoing disability.  And there is little evidence that being fit protects against experiencing low back pain in the first place.

As I said before, I’m definitely not arguing against the use of exercise as a component of rehabilitation for chronic low back pain – but at the same time, it’s really important to make sure the rationale for this is based on reality, not a myth.

Back to the findings of this review.  Firstly, is there evidence that people with chronic low back pain are actually doing less than people without? Basically, no.  But the pattern of activity can be quite different – people with ongoing tend to be just as active overall in a day, but their activity has peaks and troughs, what can be called ‘boom and bust’, or ‘saw-tooth’ pattern of activity.   Studies also show that people’s disability level is associated with their perception of how little they did – and this didn’t relate to their actual activity level.  Now that’s interesting – feeling like activities are obstructed by pain seems more salient to disability than the actual amount of activity carried out.  Perception is reality.

Are people with chronic low back pain less fit?

Several parameters are explored in this paper – deconditioning should be linked to changes in body composition (fat vs muscle), bone strength, muscle control and cardiovascular changes.

• Body fat percentages are higher in people with chronic low back pain – but bone strength is equivocal.

Muscle strength and endurance should be affected if a person is deconditioned: ‘adaptive remodelling in muscles’.   This should be reflected in atrophic changes to the muscle as well as changes to the type of fibre found in muscles.

• While some studies seem to show changes in paraspinal muscles, generalised atrophy isn’t found.  Biopsy of muscle fibres show atrophy of type II fibres, and this appears to be related to the duration of the low back pain. But the authors in this paper point out that these changes could be atrophy due to aging rather than back pain, and there were no studies to show the ratio between type I and IIX fibres in people with or without low back pain.
• Postural control studies haven’t controlled for the level of physical activities of daily living, so it’s unclear whether any differences found are due to overall low activity level (which could have existed prior to the onset of back pain), or whether any changes were as a result of doing less because of low back pain.
• Cardio fitness – well, here’s a kettle of fish.  There are loads of confounds – the type of exercise protocol used, work status comparisons, diagnostic comparisons, age and gender matching – it’s just not pretty.  This paper points out that there is conflicting evidence regarding cardiovascular deconditioning, or whether those who are working despite chronic low back pain are ‘fitter’ than those who are not, although there does appear to be a gender difference – males who are working appear to have better aerobic fitness than either women who worked outside the home, or males who did not work outside the home.  Maybe returning to work prevents cardiovascular deconditioning – but it’s unclear whether the types of work between women and men (both work in the home, and outside of the home) were controlled for.  Almost all the studies have used a cross-sectional design, so it’s really difficult to know whether deconditioning occurs after onset of pain, or prior to the onset of pain.  Low aerobic fitness and low activity levels do not appear to be risk factors for developing chronic low back pain.
• Metabolic factors – insulin insensitivity is associated with low activity levels like lots of bed rest.  Unfortunately there were not studies examining this in people with chronic low back pain, and the level of inactivity required to develop insulin insensitivity hasn’t been determined.

Now it really does get interesting for me here.  I’ve griped about the lack of validity (and reliability) of functional capacity evaluations.  They rely on people being prepared to ‘give it their best’ and for many reasons people with chronic pain may not do so.  It could their concerns about pain immediately, pain the next day, or the implications of ‘good’ performance on things like compensation.  On the other hand, a one-shot assessment isn’t able to predict performance over a day or a week – and some patients ‘over-do’, others ‘under-do’, and even the influence of the person doing the assessment can change how well the individual performs a functional test.

The authors in this paper plead for researchers to:

(1) objectively monitor general physical activity level and control for this in statistical analyses of physical fitness

(2) consider studying the factors that influence performance during performance testing in order to improve validity

(3) use longitudinal designs rather than cross-section designs to ensure correlation isn’t confused with causation – and outcome measures should monitor the impact of functional activity gains

(4) confounds known to influence physical performance usch as gender, age, recreational activities, job type, diagnosis, etc should be monitored so multiple regressions can be carried out with some confidence

The summary?

There is little research evidence that people with chronic low back pain are deconditioned either before they developed their problem, or after.  Despite this, it’s thought that being fit in a generally active way is good for overall health and especially as we age.  Engaging in more exericse does have an effect on recovery from low back pain (well, reducing the disability associated with low back pain), but we don’t know why.  Just don’t assume that because someone perceives they’re disabled, they are actually unfit.

Verbunt JA, Smeets RJ, & Wittink HM (2010). Cause or effect? Deconditioning and chronic low back pain. Pain PMID: 20153582