Psychosocial work conditions and musculoskeletal complaint : The role of affective stress response as a mediator of the effect of psychosocial risk factors on musculoskeletal complaints

The hypothesis tested in these two studies was that unfavourable psychosocial work conditions are expected to increase the risk of musculoskeletal complaints (MSC), and that this effect is at least partly mediated by affective stress responses. The testing followed Baron and Kenny s (1986) causal step approach. This means that the mediating role of affective stress responses is supported if unfavourable psychosocial work conditions significantly increase the risk of MSC and affective stress responses. In addition, the relation between MSC and psychosocial work conditions should be eliminated or significantly reduced when controlling for its effect on stress. One further requirement (only tested in study II) is that these relations should also hold after controlling for possible confounding between psychosocial and ergonomic workloads. Study I, Assembly workers: The results from the study of assembly workers showed that the relation between self-reported demands and shoulder complaints was fully explained by their relation to the affective stress response. This was taken as support for the hypothesis that the effect of psychosocial work conditions on musculoskeletal complaints (MSC), primarily in the neck and shoulder region, was mediated by the affective stress response. One weakness in the study of assembly workers was that no indicators of ergonomic workloads (awkward work positions, heavy lifting etc.) were included in the model. Although job rotation made it unlikely that ergonomic load differed very much from one assembly worker to another in the first study, it cannot be excluded that the results may partly have been an effect of confounding between psychosocial and ergonomic conditions. Another possibly critical aspect of this study was that the participants were very homogeneous with respect to work conditions. Thus it is likely that differences in self-reported psychosocial conditions reflect differences in evaluation of work conditions rather than actual differences. Study II, Hospital workers: In the second study, the stress mediation hypothesis was tested in a more heterogeneous group where there were substantial differences in actual work conditions. The study among hospital workers also included indicators of possibly critical ergonomic workload factors. The results among hospital workers did not support the hypothesis that the effects of psychosocial work conditions on MSC are mediated by the affective stress response. These results showed that the psychosocial variables were strongly related to stress and energy, and that neck and shoulder complaints were more common in the group with high demands and low skill utilisation. This was the only significant relation between psychosocial variables and MSC that was not explained by confounding with ergonomic workload. However, controlling for stress did not substantially reduce or eliminate this interaction effect. To summarise, the results for the hospital workers stand in contrast to those in the study of assembly workers