Are all workers in manual labour roles physically active at work?

Background: Physical activity (PA) at work is regularly studied and intervened upon, with those in manual labour occupations often identified as having physically active jobs. However, most of these workforces have variation in the physical demands between roles but little has been reported on the extent of this variation.
Purpose: To assess PA intensity and type within a manual labour workforce and the variation between roles.
Methods: 47 participants, within a Scottish workplace, in manual labour occupations, volunteered to take part in this study. PA was measured over a 7-day period using wrist-worn accelerometers (Actigraph wGT3X-BT) and heart rate monitors (Polar H10). Accelerometer data was classified into activity types (sedentary, stationary+, walking and running) using a random forest model (randomForest package, R software), with intensity bands (light, moderate and vigorous) mapped to each activity using established heart rate reserve thresholds. Descriptive data is presented as minutes per day (mins/day) for PA intensity bands and PA type. Participants were assigned to job role subgroups (stationary and walking) using a job exposure matrix.
Results: Median total PA and moderate-to-vigorous PA during work time were 272.2 (interquartile range 183.7-355.6) and 9.1 (interquartile range 3.1-29.0) mins/day, respectively. Workers in stationary roles spent 84.4% of their PA at work in stationary activities (sitting or standing), while the other 15.6% was ambulatory (walking or running). In comparison, for those in walking roles 77.6% of their PA at work was in stationary activities and 22.4% was ambulatory.
Conclusions: There is substantial variation of PA within manual labour workers. Choosing an appropriate PA measurement protocol is essential in evaluating physically active work roles.
Practical Implications: By identifying differences in the PA demands between workers and roles, researchers and practitioners can better tailor interventions and policies for specific contexts.

Funding: Medical Research Scotland and ACS Clothing Ltd.