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


  1. I noticed that people who have been taught lifting techniques generally use them on large loads but tend to forget them on light lifts. I’ve noticed that this applies to me too. I haven’t injured myself on large loads for years but I can’t say the same about small loads.

    1. I wonder if lifting techniques make much of a difference at all? At least the research seems to suggest that training makes very little, if any, difference to the incidence of LBP anyway. As I pointed out, I’m not sure that a biomechanical model that is simplified as much as it has been, doesn’t connect with the neuromatrix that is driving the movement patterns, and fails to account for tissue remodelling is worth very much. Especially when it doesn’t predict actual experience in the real world.
      If biomechanical and ergonomic models had strong support and make a significant impact, then I would expect the rate of reporting and disability from LBP to have reduced in the last 100 years. It has not – and has increased in many parts of the world, with devastating effects on human lives.
      There is a difference between having a sore back – and being disabled by it. The number of people who indicate they have a sore back is pretty constant around the world, irrespective of the work or economic conditions or anything pretty much – what does differ hugely is the disability and treatment-seeking associated with having a sore back. Sadly, where back pain is seen as a ‘health problem’ rather than something to do with being a human, the disability costs (not just financial costs either) are high. They’re even greater in countries where invasive investigations and treatments prevail. I’m not sure that a biomechanical model adequately explains this.

  2. Great post thanks!

    The structural-mechanical model of back pain really is getting hit from all sides right now. But it is a powerful idea and so will trump the evidence for the forseeable future I suspect. In saying that even the cherished biopsychosocial model has its limitations, particularly when it comes to producing treatments that are genuinely effective.

    What to do, what to do?!

    1. The answer to ‘what to do’ is probably to keep doing research! At least that’s my hope. The biopsychosocial model does have limitations – and so often it becomes the placeholder for what ends up being the ‘psychosocial’ model. We can’t forget the biophysical, but I think until it gets into perspective (and we have more evidence) we’re going to have trouble changing treatment habits and community beliefs (not to mention treatment provider beliefs). After all, the neuromatrix is hardly a ‘psychosocial’ model, it’s as ‘biophysical’ as blood, muscle and bone – and it’s becoming a vital link to understanding how we experience pain. Maybe I’m just hoping that there really is a ‘theory of everything’ and psychosocial aspects have some sort of direct impact on the neurological substrate of human experience – so we keep on asking questions, testing hypotheses and finding out stuff. Hooray for science!

  3. Very interesting post. I believe you are right about the acceptance of biomechanics continuing regardless of successful research. It reminds me of the research that has been done to show that child car seats have not produced any significant decrease in the number or severity of injuries or fatalities in auto accidents over regular seat belt use. The report stated that while infant car seats do prove to have significant value, once a child is able to sit on their own and stay strapped in a regular seat belt, modifed to cross their chest at optimal level, there is no statistical difference of improved safety and many incidence of failure and contributing factors to injuries sustained by children.

    1. There is a gap between scientific evidence and popular belief that takes ages to shift – I mean there are still some people who believe in a flat earth, or so I hear! There was a piece on the news in NZ recently about child car restraints suggesting that kids should remain in backwards facing seats until they’re about 5 years old, and then in a booster seat until they’re tall enough to fit into an adult seatbelt, otherwise they continue to risk injury in a collision. I can’t see too many older kids agreeing to sitting in a booster seat until they’re 14 or 15, can you?!!

  4. Excellent! I love this post. No matter how good your mechanics are, if you don’t have enough strength, your back will fail. I too believe that in 10/10 people the cause of pain or injury in the work place is multifactorial with mental state or job satisfaction being very high on the list. Thank you for exposing me to this article.

    1. Hi Jess,
      I agree with that term ‘multifactorial’ – so I don’t want to completely discount the concept of biomechanical factors, but at the same time I think we can be tempted to consider simplistic models just because they’re simple, rather than whether they explain what we see happening. Pity the health system rewards people with a biomedical approach!

  5. My son (senior in university) is taking an education course this quarter. In reading through the introduction, the importance of realizing that students are not blank slates when they enter the classroom was emphasized. In fact the role of the educator was to assess the actual conceptual (cognitive) models that a student used to gauge the necessity to not only teach new concepts but help students challenge incorrect models and discard them.
    Great example was that children often come in with “naive realism model that the earth is flat.” Then when exposed to the concept that the earth is round, they will often update their concept to either a pancake (round, flat earth) or snow globe (flat earth inside a 3-d object).
    The whole proper lifting technique model is so darn appealing because like a naive realism model of a flat earth, the notion of simple cause and effect between mechanical overload and LBP seems, well, so obvious and common sense.
    I hear a variation on this theme in many a client narrative: ” I am having pain X because I did action Y. Yes I know that was stupid or I realized one second too late that was going to hurt.” BTW please fix me pdq.
    This narrative is very comforting even if just made up by the left brain interpreter.
    I really like your point Bronnie that having a sore back can be more like having a cold–pretty common but also can be relatively minor in impact.

    1. Reading what you’ve put here is music to my ears! I think we as therapists can often elicit this discussion – ‘how did you hurt your back [neck, knee, elbow]?’ ‘Oh I think was digging [dancing, walking, turning, reaching, lifting] but it didn’t hurt at the time, it came on the next day…’
      I wonder what would happen if we just asked the person what they are doing about their back pain…and encouraged them to move normally? Would we even need to give much of an explanation? After all, do we really want to know how x-rays penetrate the body and create an image, or do we just look at the x-ray?

  6. What a great post!
    The body-as-a-machine metaphor is so pervasively accepted that we forget that it is just that: a metaphor. But machines can only be used ‘correctly’ in one way – and they come off a production line which ensures that one way is the same for every copy of the machine, regardless of the environment in which they are used. Humans just aren’t like that! I completely agree with your frustration that ergonomic and biomechanical approaches address only part of a very complex issue. We don’t just use our bodies in the workplace, and we certainly don’t use our bodies independently from thinking and emotion.
    I do wonder, though, if perhaps the focus of training shifted from limited ‘correct’ methods (as you pointed out, the real world stubbornly refuses to conform to a neat training scenario), to developing and honing kinaesthetic sense, would we see people looking after themselves better, both at work and at home, and relative to their state of mind and environment? I really do wonder….

    1. Hi Miranda, that’s a really great point – lack of kinaesthetic awareness seems to be present in many people with chronic pain (not sure if there have been any studies on this) – and something I do observe with people who over-do activity is the way they ignore discomfort and persist in an activity without moving at all for longer than most people without pain, then experience pain with high intensity. I wonder if we did listen to our bodies and then simply do something different, whether it might make a difference! ‘scuse the lack of grammar…

  7. Hi Bronnie…
    How are you doing? you’ve changed your blog! We’re featuring your blog at WFOT Congress on Friday morning – Saturday afternoon your time… and now you’ve changed the look!!!!!

    Merrolee and Anita

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