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Introduction: Ergonomic exposures do not occur in isolation – they co-occur in time. For example, to transfer a patient out of bed, a nurse might need to bend the back forward with raised arms while standing. Yet, research and workplace recommendations have targeted exposures individually, ignoring their co-occurrence in time. This study describes the co-occurrence of ergonomic exposures of mobile plant operators and cleaners.

Methods: We used data from accelerometers placed on thigh, right upper arm and upper back from 9 mobile plant operators and 157 cleaners, collected between 2011 and 2014. The data was structured in four “layers”: 1) domain (sleep, leisure and work); 2) behaviors (sit, stand and active); 3) arm elevation (above/below 60°); and 4) trunk forward bending (above/below 30°). Domains were identified from diary entries. Behavior exposures were distributed into the work and leisure domains. Arm elevation exposure was then distributed into the behaviors, and exposure on trunk forward bending was lastly distributed into the arm elevation exposure categories. We selected mobile plant operators and cleaners as occupational groups based on our assumption of them having clear differences in co-occurring ergonomic exposure profiles.

Results: On average, mobile plant operators spent most of their workday sitting (63.4% sit, 24.5% stand and 11.9% active), while cleaners spent the majority of time standing (25.1% sit, 52.2% stand and 22.6% active). Cleaners spent 5.2% (22.8 min) of their work time with arm elevation above 60°, co-occurring 64.3% of the time with standing (3.4%, 14.7 min), which further co-occurred 0.3% (4.0 min) of the time with more than 30° forward bending. In contrast, mobile plant operators worked with arms elevated above 60° for 9.4% (43.8 min) of the time, co-occurring 68.8% of the time with sitting (6.4%, 30.1 min), which further co-occurred with 1.4% (6.6 min) of forward bending more than 30°.

Discussion: This study describes ergonomic exposures across two occupations, revealing not only differences in exposure time across behaviors, arm elevation and forward bending of the back, but also in how the exposures co-occur in time. While the time with arm elevation and forward bending was comparable between the occupations, the arm elevation co-occurred predominantly while sitting among mobile plant operators, whereas it primarily co-occurred with standing for cleaners. Such differences might have implications for health outcomes, but we do not know. These findings show the need to assess not just how much time is spent on ergonomic exposures, but also what they co-occur in time with.

Conclusion: This approach of investigating co-occurrence of ergonomic exposures in time provides a method for describing not only how much ergonomic exposures occur during work, but also how much they temporally co-occur. Future research should also integrate psychosocial work factors in this approach, and investigate the importance of co-occurrence of work exposures in time for workers health.