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Dead bodies can’t feel pain, or why biomechanics and ergonomics haven’t reduced back pain

Posted May 04 2010 12:39pm


I know, it should make sense: reduce the biomechanical load on the body bits and pain/injury should reduce, right?  I mean, the maths adds up, cadaver experiments ‘prove it’, it has ‘face validity’, there is a whole industry based on the idea of  ‘safe lifting’ and injury prevention – physical ergonomics works, doesn’t it?

Well, sad to say, this very recent paper (this week’s BMJ no less!) by very respected researchers in the field has once again found that the evidence is at the most low to moderate that “physical and organisational ergonomic interventions were not more effective than no ergonomic intervention on short and long term LBP and neck pain incidence/prevalence”.

Not only does this finding fly in the face of common sense, the quality of the evidence is pretty low – and yet the amount of research has been going on for how many years?

I don’t know if many readers know, but for some years I worked as the ‘safe handling’ advisor in a large public hospital.  The whole drive of that position was intended to reduce the number of incidents of back pain (the most common ‘injury’) and the overall cost of that problem by teaching staff members that manual handling (including patient handling) needed to be carried out with thought.

Early in my career I have studied human biomechanics and I have several papers in ergonomics – but to say I haven’t been convinced that changing manual handling techniques will reduce the prevalence of back pain is understating the blindingly obvious.

So why, oh why, did I try to do this job?  Well, my main idea was that by working in that position I could begin to influence the way this organisation managed the work situation of people who developed low back pain – by supporting the person to return to work as soon as possible, by making it slightly less physically demanding for them when they did return, and to encourage staff members to support each other and to feel supported (working on the psychosocial aspects of the workplace).

I failed, not entirely miserably, but I did fail because no matter how hard I tried to show the research, very few people believed the evidence.  It simply doesn’t fit with ‘common sense’ – because ‘everyone knows’ that how you lift will affect your risk of back pain.  Not.

Why doesn’t it work?

Well, lots of reasons – one of which is pointed out in this review.  People don’t always ‘follow the rules’ when it comes to ‘safer lifting’.  This is because we don’t live in a nice, controlled environment.  While people might be taught a specific method – in the real world, the item to be moved isn’t a nice box shape, it’s a lumpy human being who squeals and flops and does the unpredictable.  In the real world, there might be little time to think and plan.  Other people might not help when needed.  The equipment might be too far away.

Oh, and maybe the assumptions of the biomechanical and physical ergonomics approach might not be correct.

You see, biomechanical equations, even sophisticated models, are still a simplistic picture of the multiple forces acting on structures – and the maths is pretty complex.

Probably more importantly, biomechanical models don’t factor in the brain – there’s a thinking, feeling, deciding, processing, dynamic neuromatrix involved in the human that is doing the moving.

Low back pain (and other musculoskeletal pains) are not a simple A + B = low back pain equation.  Researchers still haven’t narrowed down the suspects in the causal equation for low back pain.  It’s one of those delightful problems that are called ‘multifactorial’.  No single two or three or even eight factors are reliably associated with low back pain – or at least, not physical factors.  It seems that fuzzy and difficult things like attitudes, beliefs, work satisfaction, social support, supervisor interactions, peer pressure, fatigue, mood – they’re the things that seem to be associated more strongly with problems with back pain than simply the movements and forces acting on the body.

When I think of the money that is spent on training, equipment, systems and even penalties applied to reduce the physical and biomechanical demands on bodies – without addressing the brain and the person and their social setting, I despair.  Wouldn’t it be wonderful if this funding was spent on researching the psychosocial interventions that could (and do) make a difference?

Driessen MT, Proper KI, van Tulder MW, Anema JR, Bongers PM, & van der Beek AJ (2010). The effectiveness of physical and organisational ergonomic interventions on low back pain and neck pain: a systematic review. Occupational and environmental medicine, 67 (4), 277-85 PMID: 20360197


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