Details

Introduction
Previous research has shown strong associations between occupational physical activity (OPA) and need for recovery (NFR). However, this research has only utilised self-reported measures of OPA which have clear biases. Thus, there is a need for investigating if the previously documented association between self-reported OPA and NFR can be found when using technical measures of OPA. There is also the need to investigate whether older workers are particularly susceptible to increased NFR, since age related declines in physical capacity mean that it is likely these workers will have a higher NFR for a given physical activity. The aim of this study is to investigate the association between technically measured OPA and NFR, and whether this relationship is modified by age.

Methods
This study utilised data from the DPhacto cohort – comprising Danish workers (n=840) from the cleaning, manufacturing and transportation sectors. OPA was measured by accelerometers attached to the thigh and upper back for at least one work day and classified into 4 movement behaviour categories (sedentary, standing, light or moderate/vigorous). NFR was measured using a shorted version of the Danish NFR scale. Analysis was conducted using linear regression and isotemporal substitution analyses for compositional data.

Results
The overall association between OPA and NFR was statistically significant in the unadjusted model (p<0.001), but not when adjusted for age, sex, occupation and shift work (p=0.166). Isotemporal substitution showed small but significant reductions in NFR with increased sedentary time (adjusted: ΔNFR = -0.010 [ 0.019; -0.001]). There were no significant interactions between age and OPA (p=0.409).

Conclusions
This study found significant associations between OPA and NFR, but the size of these associations was small. Reallocating 30 minutes to sedentary behaviours from other behaviours was associated with a reduced NFR, but the effect size may not be practically relevant. Moreover, no clear modifying effects of age were identified.