Introduction: There is a well-established relationship between high physical activity at leisure time and decreased mortality risk. On the other hand, high physical demands at work seem to increase this risk. However, the underlying mechanism behind this effect remains unknown. Heart rate variability (HRV) measurements may bring some insight into the mechanism. Thus, the aim of this study was to determine whether HRV differs between work and leisure time among blue-collar workers.

Methods: This study was based on data from the cross-sectional NOMAD study among blue-collar workers from seven workplaces in Denmark. One hundred thirty-eight blue-collar workers, which had at least 7 recording hours during work and leisure time were included in the analysis. Data from physical activity and HRV were obtained for four days using tri-axial accelerometers (Actigraph GT3X+) and heart rate monitor (Actiheart), respectively. Parametric (paired t test) and nonparametric (Wilcoxon signed-ranks test) tests for pairwise comparisons were applied to compare mean HRV indices in time and frequency domains between work and leisure time.

Results: The mean age of the workers was 45.2 years, 51% were females, 42% were smokers, 18% reported lifetime occurrence of hypertension and 45% reported to perform lifting and carrying for more than half of the work time. A significant higher overall HRV was found during leisure time compared to work. Leisure time showed higher parasympathetic nervous system (PNS) measures of HRV (p<.05), while sympathetic nervous system (SNS) related indices (p<.05) were reduced in comparison to work.

Conclusions: Leisure time showed high HRV and PNS indices and work time showed high SNS-related indices. The higher SNS modulation during work can be related to a greater risk of developing heart diseases among blue-collar workers.