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

- Sustained attention tasks impose high levels of mental workload.
- Increases in attention-related mental workload coincide with decreased in end-tidal CO2.
- End-tidal CO2 moderates the relationship between attention-related mental workload and upper trapezius muscle activity.

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.