Introduction: Physical inactivity is a known risk factor for low back pain (LBP) disability, yet the relationship between objective quantification of daily physical activity pattern and its relationship with pain-related limitations are still sparse among the LBP populations. A better understanding of the connections between routine physical activity and pain-related limitation may lead to better prevention strategies and improvements in LBP rehabilitation.  In this study, we aim to objectively characterize the free-living physical activity patterns of people with LBP using a wrist-worn accelerometer (Actigraph), and to investigate the connection between physical activity patterns and pain-induced limitations.

Methods: As part of a clinical trial of pain management skills class (NCT03167086), eighty-two LBP participants’ (51% female, mean 51.8 years old) wore an Actigraph GT3X+ sensor on their non-dominant wrist for at least 7 days prior to the intervention. Waking hours (5 am-midnight) signals were extracted to derive the following physical activity data: step count, sedentary time, moderate-vigorous physical activity (MVPA) time, and hourly activity accumulation (step count). Associations between physical activity and patient-reported outcomes (pain catastrophizing scale, LBP pain bothersomeness scale, PROMIS pain interference, PROMIS physical function, etc.) were examined. Among all selected PROs, the pain interference index demonstrated the strongest relationship with the hourly activity accumulation, thus activity data were further divided into three terciles based on the pain interference index to identify potentially sensitive activity markers for stratifying LBP cohorts.

Results:  Daily macro physical activity including total steps, sedentary time, and MVPA time were not associated with any patient-reported pain outcome, and were not able to stratify the LBP cohort based on the pain-interference index. However, the hourly activity accumulation pattern identified a distinguishable morning/evening activity pattern that can stratify the LBP cohort. More specifically, individuals in the high pain interference tercile accumulated significantly fewer steps in the morning hours (9-11 am) than those in the low pain interference tercile (600 vs 800 steps per hour), and significantly more steps (350 vs 200 steps per hour) during late-night hours (10 pm to midnight).

Discussion: Even though the total amount of daily physical activity was not associated with any of the pain-related measures, we observed a unique morning/evening activity accumulation pattern that was associated pain interference.  Future research is needed to investigate the underlying mechanism for the differential activity patterns between individuals with low/high pain interference, and to investigate whether such activity patterns can be used to optimize individualized LBP rehabilitation programs.