Organizational Risk Factors for Musculoskeletal Disorders: Theory and Evidence

Steven L. Sauter

ABSTRACT

Thank you. I want to begin by thanking Steve Lamm and conference organizers for us in NIOSH and myself to participate in this interesting meeting. I want to begin by just reading a few lines from an abstract of a scientific report that was published recently.

Three hundred and ninety-four healthy subjects were given nasal drops containing one of five respiratory viruses. And an additional 26 were given saline nasal drops. The subjects were then quarantined and monitored for the development of evidence of infection. Clinical colds were defined as clinical symptoms in the presence of an infection verified by the isolation of virus or by an increase in virus-specific antibody. The rates of both respiratory infection and clinical colds increased significantly in a dose-response manner with increases in the degree of psychological stress. These effects were not altered by age, sex, education, allergic status, weight, season, number of subjects housed together, the infectious status of subjects before the study and virus-specific antibody status at baseline.

Now, I'=>m sure many of you are probably scratching your heads wondering if I came to the right conference. But the reason I bring this up as a beginning is that it'=>s a very compelling example of the importance of psychological or psychosocial factors in influencing the health of individuals. And that's what I=m going to be talking about today. This is a subject that'=>s of increasing interest in occupational health, and an area of long time study in psychology and in health psychology. And we=re now seeing greater manifestations of this in the occupational health literature. This is a '96 publication from Occupational and Environmental Medicine that is really not a holistic model in that it suggests research, but it illustrates, it's a model of illustrating or suggesting the importance of psychosocial factors in occupational health outcomes. And it=s actually a very simple model suggesting that there are really two pathways, a physical pathway from hazards to symptoms and also a psychosocial pathway. And in the psychosocial pathways are a lot of effects, many of which were mentioned by Bob Bettendorf. I won=t go into those in any detail. I want to show you one more though that is a little bit more familiar and has captured a lot of attention. Although, again, it's really just a metaphor more than an explanatory model. And it=s the iceberg model of disease offered by Bruce Hocking who is an occupational physician at Telecom Australia. Basically the metaphor is that you have clinical and sub-clinical disease in the environment. And the environment really can be considered a psychosocial sea, and the sub-clinical disease is that part of the iceberg that floats below the sea and so that the clinical disease becomes more apparent obviously as a function of clinical disease in the work place, but also as a function of the density of the psychosocial environment that is the nature or the degree of stress in the workplace psychosocial environment. So, giving specifically to the subject of this meeting which is musculoskeletal disorders, there is evidence that'=>s been available for some time that has indicated that psychosocial factors are important in the etiology of these disorders, or at least somehow interact with physical stressors in the work environment. Again, I'm just going to cite from a study. This is an electromyographic study of typists.

In these tests, we began by isolating a single motor unit potential during repeated striking of a typewriter key whereby any change that might have occurred in the number of electric oscillations could be easily noted. The more the writers concentrated their attention on the task, especially if they were sharply commanded to do so in an impatient and stern tone, the greater the number of action potentials recorded.

Now you can probably tell by the words that this is not a recent study. Actually it was a study by A. Wondervolt in 1951. Really one of the first studies to show an influence of psychological stress in the environment on the physical action of keying. And our data today which now reproduce these findings. Of interest is the conclusion of Wondervolt. He says the psychic variability is possibly of far greater significance in typewriting than the external factors such as office equipment, lighting, etc. I don't know if we can really make too much of that statement given the conditions of this study, but it's his impression. Now since that time there have been a great number of studies, both in the office environment and in industrial situations suggesting the importance of psychosocial factors. There are probably 20 good studies that deal just in the office environment and another 20 to 30 in the industrial environment. Several authors have reviewed this work, but the most comprehensive review was by Netherland'=>s investigators Pauline Bongers who concluded in her review that monotonous work, high perceived workload and time pressure are related to musculoskeletal symptoms. In addition, the data suggests that low control on the job, lack of social support, again, some of the variables listed by Dr. Agnew, are positively associated with musculoskeletal disease. Perceived stress must be intermediate in this process. So, one rather affirmative conclusion, but still I would say there'=>s a lot of uncertainty in this area. NIOSH has contributed to this research on psychosocial factors and musculoskeletal problems at work in many ways. This is a fairly recent study that many of you may be familiar with at U.S. West Communications. And what I=ve done here is just to point out different body parts where musculoskeletal problems were influenced statistically in the analyses by psychosocial factors. And we see actually quite a few effects at the wrist in both forearms and the right wrist and the neck and so forth. More recently is a study that was just completed and published within the last couple of months from our laboratories in the applied psychology and ergonomics branch. This was really a study of electronic performance monitoring of workers. And what we did was, a study by Larry Schliffer, Tracey Golinski and Chris Pann, two study groups were identified - these were all professional typists, highly skilled. They were subdivided into two groups. One group was subjected to electronic monitoring. And the second group, and that'=>s this group, performance monitoring. This group was also subjected to a performance standard. So they were monitored electronically, they were given a standard number of keystrokes they had to achieve per hour. When they did not make this threshold, they were then given feedback indicating this. So we study them over several days and at the end of the study, the groups were broken into three subgroups - low performers, moderate performers, high performers - same keystroke rates in both groups. The moderate performers were the individuals who could just barely make the threshold for the performance standard, which was about 200 keystrokes per minute. Well, we looked at stress in this group and what we found is consistent with other psychological research and with what probably many of you are thinking right now in that when we compared the monitored group with the non-monitored group, it was really only this middle group - the moderate performers - those that could barely meet the standard that experienced much stress.

These are significance levels for four different types of outcomes, workload to satisfaction, time pressure, irritation and tension. And you see the effects or the stress really seems to be apparent right here. And again this is consistent with conventional wisdom. We know in studies that it=s really not the top dog that is stressed out, it'=>s the one that's trying to be the top dog. And that's what these people were trying to do. When we look at musculoskeletal symptom differences between the monitored and non-monitored group, this is what we found. The monitored group over the course of several days gradually reported more and more symptoms, but guess what? Where do these symptoms occur? Again, they only occurred in this moderate performer group that also experienced the stress. So, a more controlled study indicating evidence of some type of influence of the psychosocial environment on musculoskeletal outcomes. That was just reported in the Journal of Human Computer Interaction.

Now, in contrast to models that I=ve showed you at the beginning of my discussion. In our branch we have developed a fairly complex explanatory model showing different pathways between the psychosocial environment and the physical environment and health outcomes. And I'=>m going to discuss this model, but I'=>m going to give you only the brief version of it. In the simplest form what the model says is that of course, physical, chemical, biological stressors in the workplace are related to occupational injury and illness, and that there is an influence of work organization that really occurs by two mechanisms. One is an exposure mechanism. The model suggests that work organization directly influences exposure of workers to physical stressors in the workplace. There's no psychology involved. There's no psychological mediation whatsoever. The conditions of work organization merely increase or decrease exposure to these physical stressors. The other pathway is a psychological pathway and is much more controversial and the evidence is much more shaky here in the area of occupational health. If you go back to the literature in health psychology, one finds stronger evidence of this mechanism. So what I want to do today is just talk a little bit about this model and what I would like to do is try to have you go away from this meeting with a better understanding of the possible ways in which work place psychosocial factors can influence musculoskeletal outcomes, and to think about and use this information to better design research and interventions on this problem.

Before I get into that, I want to just mention a couple of caveats. Just like in the opening example where stress was shown to influence infection, by demonstrating that, that did not reduce or nullify the effect of the infectious agent. By the same token I want to be very clear that when I talk about a psychosocial factor it's not an either/or proposition. The fact that we are demonstrating that psychosocial factors have a role does not mean that physical factors don=t have a role. There=s some type of interaction and complimentary arrangement that=s going on. So I don=t want you to think that I'm denying the role of ergonomic factors. In fact, in the area of office work we=ve published one of the very few studies which demonstrated fairly affirmatively that ergonomic factors, at least in VDT work, are influential. This study published in '91 indicated that the effects of ergonomic factors on musculoskeletal discomfort were clearly evident in the analyses of that work. The other thing that I want to mention is that because much of my experience is in the area of office work and VDT work, that=s what I=ll be talking about. That doesn't mean to suggest that the problems are greatest there or exist only there. I don=t mean to imply that. It's just that that=s where my experience is, so I'll draw on those examples.

Now, I think one of the biggest problems in this area is everybody's kind of doing their own thing. And this is a growing area. There are many different perspectives on what psychosocial factors are. Since I began talking I've used the word, stress, work organization, psychosocial factor, psychosocial environment, etc., etc., etc. And it=s a very confusing mix. So what I want to do is try to, following from some of the things that Jackie said, impose some standardization or at least some simplification to help with the understanding of this area. The way I think of it, we can consider the work environment to consist of basically two types of stressors - physical stressors and psychosocial stressors - or parallel to that, we can think of physical demands being exerted on the worker and psychological demands being exerted on the worker. So, it=s a very gross simplification but I think it works. So those are the two major dimensions of work in my view. And I think we all are very familiar with the concept of physical stressors. I mean, this is the basic kind of industrial hygiene or ergonomic view that physical stressors, the tools we use at work, lead to some kind of physical demand, producing some kind of biological or chemical strain, resulting in illness or injury. Parallel to this, to the physical stressors are psychosocial stressors in the workplace which cause psychological demand and result in some type of psychological strain or stress on the job. The question is, what am I talking about when I'm talking about psychosocial stressors? It's convenient to group psychosocial stressors, and conventional in psychology, to group them into two categories - work organization and also individual factors. Both of these give rise to psychological demands. Work organization as I'=>ll illustrate in just a moment also results in physical demands. But if you look at this, what I have here, many of you will see through experience that this is the conventional or classical job stress model. The classical job stress model suggests that work organization results in psychological demands at work, then psychological strain and stress, and that these effects are moderated by individual factors. Importantly from a NIOSH perspective and from my perspective, work organization takes primacy in this model and individual factors serve as moderators. Now, again, to take one step down, what am I talking about when I talk about work organization and individual factors? Work organization refers broadly to the way work is organized, structured and managed. It includes by convention but not limited to these factors, organizational practices - is it a participatory management? - interpersonal roles, supervisory relationships, the design of tasks, how narrow or complex are tasks? Career concerns, job ambiguity was mentioned earlier, and the roles that workers have. Too much responsibility, too little responsibility, etc. Personal factors pertain to factors such as age, gender, personality, physiology, family demands, prior learning, etc. You've heard many of these in earlier presentations. So, that=s kind of a simplified classification scheme that I like to use that I think helps understand the concept of psychosocial factors and their relationship to specific aspects of work. Now, so then what I'm suggesting is that this psychosocial stress model exists parallel, or is an aspect of the environment that exists parallel to the physical demands in the environment. And that the psychosocial environment impacts this physical stress process in several ways. And I=m just going to conclude with examples of this influence and say a few words about what we know, and about where we need to go with the research in this area.

First, is this pathway between work organization and the physical stressors in the work place. This is the one I showed you earlier in the brief model. It'=>s the exposure influence. Basically, it'=>s suggesting that work organization factors, let=s just pick one such as highly monotonous or repetitious work. So if we take a complex task, break it down, make it very narrow such as what happened when the industrial revolution occurred, that influence is exposure to physical stressors. This is exactly what happens with repetition. In the office workplace, here=s an example of this. In word processing. Here is a statement by one writer, Aword processing operators are specialized production technicians, they are not secretaries who are responsible for performing various administrative tasks. They should not be responsible for answering phone calls and negotiating work orders, etc.@ So you can see how with the introduction of the industrial office which wasn=t specific just to VDT=s, it happened with typewriting back in the '=>20=s and >30=s, that that created a narrowing of that job. We all know that that is stressful work. It =s fatiguing work. So there you have a psychological demand, but at the same time, what does it do? It increases the amount of repetition. So there=s a very clear pathway between work organization and physical demand. The real question is, when you consider the stresses that we experience in the workplace, can we understand all their effects to be going through this pathway, or is there actually something left over that is more psychological in nature that leads you to this illness and injury? That, I think, is really the key question that epidemiologists and ergonomists are grappling with. Only a few studies have looked at both these psychosocial factors and physical factors concurrently and conducted analyses which look at whether there is something effect related to the psychosocial environment after looking at the effects of the physical environment and adjusting for these factors.

The second pathway, again, is the more uncertain and a bit more controversial, and that is whether the psychological effects resulting from work organization are influencing this illness pathway. There is some evidence that indicates that this is so - that there are psychosocial mechanisms operating. One of them that we are perhaps most familiar with is the concept of psychogenic muscle tension. Here are some examples from Norway. They show workers working at a computer terminal, and they =re performing either complex or simple reaction time tests. Complex, simple, complex, simple. Running short on time. Okay. I=m going to wrap it up then. So, this is the Wundervolt, this is the thing I started out. The fact that Wundervolt indicated early, 1951, that psychological stress increases muscle tension. What we see in this data is that the complex reaction time results across all of these, these are different subjects, A through D, and we see high muscle tension, low, high, low, high, low. The magnitudes vary. So one of the key questions here is, is it individual differences or is it task effects that are related to this muscle tension? There=s been a great propensity by people who have looked at this to put more focus on the individual than on the nature of the work. But clearly these data do show a work related influence.

The last pathway is even more tenuous and more difficult, but I think we cannot afford to ignore it anymore in the epidemiologic research, and it is this one right here. Basically what it suggests is that psychological factors influence the recognition or perception and reporting of symptoms. And just with one last slide, maybe try to impress on you the significance of this. It=s a study that just appeared in the Journal of Personality and Social Psychology, and for those of you that are interested in this I strongly recommend looking at it because it does cover this whole area of research very well in the health psychology area. Here=s what these investigators found:

The present study confirmed the previous research findings that unpleasant affective state, namely, your moods, how you feel at present, bears a strong concurrent relation to the frequency of reported physical symptoms. The findings have implications for the conduct of research in the health field when self reports of physical symptoms are used.

There are now probably six or seven well done studies that do show that current mood, perhaps as affected by the job in terms of job dissatisfaction, is influential in affecting how people probably recognize and certainly report symptoms in work. So, from a research perspective it=s important that studies begin to consider these by including measures of mood or affect in their study design. So I have some other conclusions, but I think I can save them for the wrap-up session. Thank you very much.