Cardiorespiratory fitness, occupational aerobic workload and age. Workplace measurements among blue-colllar workers

Background: The knowledge from laboratory studies dating back to the 50’s on the importance of the association between cardiorespiratory fitness and aerobic workload for workers health is fundamental for promoting sustainable healthy employability among ageing blue-collar workers today. However, the association between cardiorespiratory fitness and aerobic workload has not been documented using technical measurements during daily work, and we do not know if it applies to normal work of blue-collar workers in different age groups today. Aim: We aim to investigate the association between cardiorespiratory fitness and aerobic workload among blue-collar workers using measurements of 24-hour heart rate collected over consecutive working days. Methods: We analyzed baseline cardiorespiratory fitness, assessed using a sub-maximal cycle ergometer test, and 1 to 4 days of 24-hour heart rate measurement from 497 blue-collar workers participating in the DPhacto study. We assessed the association between the aerobic workload defined as the average percentage of heart rate reserve (%HRR), maximum %HRR and the duration time spent at a high HRR (> 30%) during working hours. The association was assessed using multivariate linear regression models adjusted for age, sex, self-perceived health, shift-work, prescription medication and occupation, as well as for different strata of age. Results: Higher cardiorespiratory fitness was significantly associated with decreased mean %HRR -0.32 [95%CI: -0.39 to -0.25], maximum %HRR -0.35 [95%CI: -0.45 to -0.25] and time spent at ≥30% HRR -1.8% [95%CI: -2.2 to -1.5%]. These associations were evident across age groups, with slightly stronger associations for workers aged 46-51. Conclusions: Higher cardiorespiratory fitness was associated with decreased aerobic workload during normal work in all age groups of blue-collar workers. Our findings highlight the need for including cardiorespiratory fitness when evaluating the aerobic workload of blue-collar workers, being of relevance in the promotion of healthy sustainable employment of blue-collar workers.