Intensity of occupational physical activity in blue-collar workers: do self-reported rating and device-worn measurements agree?

Purpose High intensity occupational physical activity (OPA) seem to aggravate health and increase risk of sick leave and early retirement. Most intensity of OPA monitoring has been self-reported, e.g. by rating of perceived exertion (RPE). However, no studies have investigated the precision and risk of bias in RPE reporting during free-living OPA. This study investigated the agreement between OPA intensity in percentage of the heart rate reserve (%HRR) estimated from RPE and device-measured heart rate (HR), and potential bias factors on this agreement. Methods The CR10 scale measured RPE at work. The Actiheart monitor measured HR during 24-h a day for 2–4 days. Both RPE and device-worn HR were converted to %HRR. The difference between both %HRR and their limits of agreement was determined in a Bland Altman plot. To detect bias factors, the difference between both %HRR was regressed on age, sex, cardiorespiratory fitness, occupational lifting, medication, consequences of musculoskeletal disorders and the interactions between these factors with device-work %HRR. Results Six hundred and twenty-three participants were included in the analysis. Mean difference between RPE-based and device-worn %HRR was 54.6% (SD 19.5). The limits of agreement were wide (11.6–90.1%HRR). Age (0.48%HRR, 95% CI 0.18–0.79) occupational lifting (9.84%HRR, 95% CI 3.85–15.83) and cardiorespiratory fitness (0.41%HRR, 95% CI 0.03–0.79) significantly biased the agreement between the estimations of OPA intensity. Conclusion RPE overestimated OPA intensity, and was biased by several factors. Device-worn %HRR should be preferred when evaluating OPA intensity among workers with physically demanding jobs.