The moderating role of end-tidal CO₂ on upper trapezius muscle activity in response to sustained attention

With higher levels of automation in modern manufacturing, there is increased monitoring of the process by the human operator. Prolonged monitoring or sustained attention has been found to be stressful for human operators. Plant and process operators have also been found to have one of the highest level of work demands (work speed, pace) in a recent European survey (Eurofound, 2015). Along with this, the incidence of Work Related Musculoskeletal Disorders (WRMSDs) remains at a high level in the manufacturing sector. This research endeavoured to determine if end-tidal CO₂ levels decreased and upper trapezius muscle activity increased concurrently with increased levels of attention. We then developed a model to investigate if end-tidal CO₂ moderated the relationship between mental workload due to sustained attention and upper trapezius muscle activity. The resulting interactional model found that end-tidal CO₂ moderated the relationship (p = 0.004) when end-tidal CO₂ reached the hypocapnic range (>35 mm Hg). This model indicates the possibility that a high level of sustained attention is a risk factor in the development of WRMSDs and should therefore be included in workplace risk assessments.