First published in Health and Safety at Work Magazine, January 2018
In the 17th century, scientist and philosopher René Descartes proposed that we experience pain when specific pain fibres transmit a signal from an injury to the brain, an idea reinforced during the 19th century by efforts to localise pain receptors. Attempts to control pain by identifying and removing pain fibres carried on into the 1950s, although the results of such operations were inconclusive. By 1965, a different mechanism had been proposed: psychologist Ron Melzack and neurophysiologist Patrick Wall published their theory that perception of pain is based not just on tissue damage, but on previous experiences and attitudes.
Fifty years on, although many other authors have written about the social, psychological and behavioural dimensions of pain, the model of musculoskeletal (MS) pain that has persisted in manual handling and display screen equipment (DSE) legislation, training and risk assessments has remained a largely physical one. In other words, damage to tissues is caused by too much load, moved too often or too quickly, using the wrong lifting technique, or by sitting on the wrong chair at the wrong height and hitting the keyboard too often. This damage in turn causes pain.
The model has been reinforced by respected bodies. For instance, a 1999 report from the European Agency for Safety and Health at Work (EU-OSHA), Work-related neck and upper limb musculoskeletal disorders, describes the key risk factors as working in painful positions; moving heavy loads; short repetitive tasks, repetitive movements and working at high speed.
But there was a change in tone in March 2017, when the HSE’s Workplace Health Expert Committee (WHEC) produced a report, Work-associated musculoskeletal pain: the role of HSE, which identified “compelling evidence that musculoskeletal pain and its consequences are not solely caused by mechanical factors in the work environment.”
The WHEC cited research showing that psychological distress and poor mental health are better predictors of new onset low back pain (LBP) than physical risk factors, and that workers dissatisfied with their occupation, their place of employment or social situation experience more LBP than happier colleagues.
If musculoskeletal pain was simply a function of load, frequency and duration, we might expect fewer reports in the workplace now than in the 1950s, when work was generally more physically demanding. In fact, the number of days of LBP disability claimed through social security rose by a factor of eight between the 1950s and the 1990s. According to the HSE’s most recent statistical update, the incidence of musculoskeletal disorders (MSDs) per 100,000 workers has remained relatively unchanged for the past six years.
Even amongst children, the WHEC found that the correlation between emotional problems and LBP is stronger than the correlation between LBP and the weight of schoolbags, or schoolchildren’s sitting posture.
The WHEC also points to evidence that the same occupations in different countries experience different prevalence rates of MSD. The committee cited a study by Coggan et al (2013) which found huge differences between different countries: disabling LBP was reported by only one in ten nurses in Pakistan and Japan compared with around four in ten in Nicaragua and Costa Rica. For office workers, a similar pattern emerged with just over 2% of workers in Pakistan and Japan reporting disabling wrist/hand pain, compared to nearly a third in Brazil and Nicaragua.
Whilst workload factors and the availability of sickness benefits might have been a factor behind different levels of sickness absence claims, these would not explain the differences in reported levels of pain.
There are two possible explanations as to why the MSD pain in individual experiences is affected by factors that aren’t directly related to the physical demands of the job. The more familiar “psycho-social environment model” suggests that individuals experience more pain in certain workplace scenarios, for instance when they are under pressure to hit targets. But the second explanation, to which the WHEC is alluding, is based on an alternative understanding of how pain is generated.
Evidence that manual handling training alone does not in itself reduce reported MS pain has sometimes been explained by looking at the physical impact of the psycho-social environment. In an unsupportive environment, tasks are poorly designed, while people are forced to adopt unnatural postures or to work at a forced rate, and they do not feel able to ask for help. For example, a nurse in a poorly staffed care home might feel compelled to lift an elderly and loudly complaining patient on his own, rather than seek help; and a worker in a call centre who can’t take a break when she needs to might suffer more than a similar worker who is permitted more frequent breaks.
John Jackson, a qualified sports therapist who also offers manual handling training at Alistair Bromhead, sees some validity in this explanation, having observed how pressures in the workplace leave people feeling they don’t have the time to adopt “neutral” postures. “We see this in DSE and manual handling related tasks, where workers who are under pressure – tight deadlines – will adopt non-neutral postures for prolonged periods. All of this contributes to MSDs.”
Research commissioned by the HSE from Loughborough University on how to reduce MSDs in the workplace (RR 545, 2007) recognises the role of psychological factors, but sees these as influencing the uptake of safer handling practices rather than as a cause of pain in themselves. The research concludes that one of the most common facilitators to reduce handling risks is supportive management.
However, whilst the perception of low support is often correlated with reported pain, this is not substantiated by an evidential link between poor management support and a requirement for more lifting. For example, a study of nurses (Smith et al, 2004) showed that whilst nurses who felt less supported experienced more pain, they did not actually do more lifting than those nurses who did not report MS pain. In other words, psycho-social environmental factors alone are insufficient to explain how pain is generated and experienced.
In Beyond biomechanics: Psychosocial aspects of musculoskeletal disorders in office work (1996), Tores Theorell, a Swedish expert in psycho-social factors in human health, provides one explanation as to why lifting the same load might cause more pain when someone is stressed. Electrical activity can be measured in muscles used for lifting, and a similar electrical activity can be measured in people experiencing stress, even when muscles should be at rest. Theorell suggests that the combined activity in the muscles might mean that a worker feeling stressed will experience more load in the muscles than when he or she is not stressed, given the same manual-handling task.
A further explanation could be that lack of sleep and an imbalance of hormones, caused by stress or depression, inhibit the body’s normal repair and growth mechanisms, leaving people less able to recover between manual handling tasks. However, Theorell’s explanation still relies on there being a localised physical cause of pain: a task putting more load on a muscle, topped up with an additional load created by a physical reaction to stress.
Other theories consider pain to be part of an evolutionary mechanism that teaches us to avoid harm. The pain experienced if you touch something hot has a purpose – to send a message to the brain to “stop touching the hot thing”. Pain when carrying something heavy or adopting an awkward posture is therefore a signal to tell the brain to stop doing the thing that hurts. Once damage has been done, pain might continue as a way of telling the body to take it easy while the area recovers, for example not putting weight on a twisted ankle.
However, it’s generally agreed that a non-functional type of pain can continue to exist, even when there is no longer an immediate cause of the pain, nor any tissue damage. Osteopath and yoga teacher Peter Blackaby often comes across patients and students who continue to experience pain beyond its “useful” phase, and believes that our pain signals are modified by expectation, experience, anxiety and a background sense of wellbeing.
“If I stub my toe, it might hurt more if I am cold and miserable, and less if I am happy and excited. The same information is modified by my state of mind, to amplify or downscale the sensation.” Blackaby sees a similar phenomenon in clients for osteopathy and for yoga lessons. “If someone in their 40s has been told that their joints are wearing out, when they feel a strain in their back the signal is modified by that belief and the pain experienced is amplified and focused on. This is how chronic pain often begins,” he says.
Blackaby refers to the concept of “neurotags” developed by clinical scientist Lorimer Moseley, a researcher in pain perception currently based in Australia. Moseley’s theory suggests that the brain creates “neurotags” for particular outputs, which could be pain, thoughts or immune system responses. But as different “neurotags” may contain the same member cells, the activation of one “neurotag” becomes easier when its neighbour is triggered. “In some cases, this ‘tagging’ [and activation] becomes extreme until almost any movement hurts and we retreat into immobility, which aggravates the problem further,” Blackaby suggests.
Georgie Oldfield is a physiotherapist who specialises in helping people to recover from chronic pain. Frustrated that her patients’ symptoms didn’t conform to any physical diagnoses, she too looked for alternative explanations, coming across Dr John Sarno’s theory of “tension myoneural syndrome”, or mindbody syndrome. Sarno does not restrict his theory to musculoskeletal pain, but believes that ulcers, heartburn, irritable bowel syndrome and headaches could also be explained by a stress reaction.
Oldfield explains: “All pain is real and is caused by activated neural pathways in the brain which become learned. The trigger might be due to a physical or emotional incident and can lead to persistent activation of the flight or fight response, resulting in pain, weakness and other physiological changes in the body.” Oldfield agrees with Blackaby that pain can be fuelled by the very diagnosis meant to help. “Negative beliefs about pain have been linked with acute pain becoming persistent and increasingly debilitating.”
Manual handling trainer Jackson also lays some responsibility with the medical profession. “Negative expectation of injury can be fuelled by the prevalence of imaging techniques by medical professionals, highlighting ‘degeneration’ in tissues and all the negative connotations that this implies, when it’s only wear and tear, which is usually manageable.”
In the Coggan et al study, the authors identify a dilemma: whilst good ergonomic practice, including training and job design, can reduce physical stresses that lead to pain, there is a danger that it can “promote an exaggerated belief among workers that they are exposed to serious risk of injury, and thereby cause a paradoxical increase in symptoms and disability”.
Jackson recognises this risk, having seen many patients who feel themselves to be “victims”. “They blame others for their ailments: ‘The company should have done this or not made me do that.’ A better long-term outcome will typically be experienced by those with a positive mental attitude who are willing to take responsibility for their own recovery and take steps to work on their posture, improve their core stability and take active steps to make changes to remove the original aggravating factors and prevent recurrences.”
The WHEC report suggests than in addition to creating an “ergonomically friendly work environment and reduced physical loading”, employers should be “taking a visible interest in employees’ welfare”, even if the result of this is purely a Hawthorne effect. In other words, it is the interest from a third party that brings about an improvement, rather than specific changes in the environment.
However, Coggan et al’s caution should make us think again about how we take that “visible interest”. A traditional approach to health and safety training has been to start with the results of not acting safely – the gory accident photographs, the video of a bereaved widow, or the picture of the inflamed vertebral disc. Such training tells the learner: “This job might hurt you. Watch out for pain. Think about it and tell us about it.”
The understanding gleaned from Coggan suggests that our approaches to training should be more positive. Whilst aches and pains should not be ignored, they should not be catastrophised. Instead, they should be acknowledged and responded to appropriately, for example by changing to a different activity. The body’s normal response to work should not be dwelt on as a sign that we are getting old or ill, or by deciding that all activity must cease (see case study, below). The WHEC report also advises that discussions about ergonomics shouldn’t focus on the avoidance of major injury, but instead talk about “benefits to worker comfort, long-term wellbeing, and business productivity.”
Jackson’s advice chimes with this. Rather than focusing on loads and lifts, or chairs and keyboards, he suggests: “Employers need to take a holistic approach to wellness in the workplace, and consider where they can support issues of work/life balance, time management, peer pressure, managerial pressures and psychological health.”
However, where pain continues despite an employer’s best endeavours, there are options. Removing other sources of stress in the workplace, or easing stress caused by work-home-life conflicts, will benefit everyone. For individuals suffering pain, referrals to a therapist who can help to “unmap” the movement-pain responses can be considered, or yoga, mindfulness and relaxation classes.
Where pain persists, Oldfield turns to emotional issues, encouraging individuals to acknowledge and express their feelings. (Sarno’s work with back pain patients includes asking them to write about their emotions.) “For many, recovery is possible through educating them, and by changing behaviours that might be unintentionally keeping pain ‘turned on’. Even the simple question, ‘What was going on in your life when the pain began?’ can help an individual begin to consider the impact of psycho-social stressors on the onset and perpetuation of their symptoms,” she says.
Suggesting that pain has a psychological mechanism is not an excuse for failing to make sure that the workplace and work tasks are well designed. Hazardous handling tasks should be eliminated, and the remaining tasks designed to reduce the risk factors of repetition, awkward postures and time pressure.
However, the HSE has recognised that purely mechanical explanations for musculoskeletal disorders are no longer sufficient. Just as Pavlov’s dogs learnt to associate a bell with food, so we workers can learn to associate particular movements or environments with pain. If employers want to tackle the epidemic of MSDs, new approaches – incorporating positive messages and a better understanding of the mind-body interface – will be needed.