In-Field Ecological Momentary Assessment From Wearable Motion Sensors and Self-Report in a Chronic Low Back Pain...

Chronic low back pain (cLBP) is a prevalent and debilitating condition. Gaining insight into the daily experiences of those with cLBP is crucial for developing effective management. Pain and activity are typically assessed at a single time point and often rely on retrospective self-reports, which can be prone to recall bias and may not reflect the day-to-day variability of these experiences. As a part of the University of Pittsburgh LB³P Mechanistic Research Center, this study used ecological momentary assessment (EMA) and wearable devices to collect real-time data in a large cohort of adults with cLBP. The primary aims were to collect and characterize pain and activity profiles of individuals with cLBP.

This study enrolled 1007 adults with cLBP who met the National Institutes of Health defined criteria. Over 7 days, participants were assessed in their own environment. EMA was gathered in real-time via a custom mobile app, prompting participants three times daily to provide their perceptions of current pain intensity (0-10), pain interference (0-10), and activity level (very light to vigorous). Time of falling asleep and waking was also reported. Participants wore ActiGraph GT9X devices on their wrist and waist. A custom back sensor was also adhered to the skin over the lumbar (L5) segment. Activity counts, wear time, and step counts were calculated, utilizing algorithms provided by ActiGraph. Sensor data were filtered to include at least 4 days of 10 or more hours each. Activity counts were categorized into sedentary, light, and moderate-to-very-vigorous based on Freedson Adult cutpoints.

Out of 1007 participants, 989 submitted EMA data (58.8 ± 16.5 years old; 40% male and 60% female; mean pain intensity at enrollment of 5.4 (SD 2.1) and a median of 5 (interquartile range [IQR] 3) on a 0-10 scale; mean PROMIS Pain Interference T-score at enrollment of 60.5 (SD 7.5) and a median of 61.2 (IQR 9.6)). The median reported pain intensity level from the EMA was 1 (IQR = 3), while pain interference was 3 (IQR = 3). More than half of the participants reported a median pain intensity of either 0 or 1 (54.0%) and a median pain interference between 0 and 3 (57.4%). Most participants self-reported their activity levels as moderate (36%) or light (33%). Based on pain ratings during each day, most participants had their pain intensity (30%) and pain interference (40%) peaking in the evening. ActiGraph data from 884 wrist-worn and 785 waist-worn devices were analyzed. Wrist data showed a median of 1 765 325 (IQR 796 995) activity counts/day and 9575 (IQR 4228) steps/day. Waist data showed 358 390 (IQR 223 758) activity counts/day and 4114 (IQR 3146) steps/day. The percentage of daily sedentary activity was 47.3% for wrist and 72.8% for waist. The back sensor data from 586 participants showed a median of 340 345 (IQR = 223 399) activity counts/day and a median of 3695 (IQR = 2743) steps/day. The percentage of time spent in daily sedentary activity was 82.6%. Both ActiGraph devices and the back sensor indicated that the majority of the time was spent in sedentary activity level, which is lower than the activity level reported in the EMA.

Despite having cLBP with self-reported moderate pain levels, participants generally reported periods of relatively low levels of pain intensity and interference in their EMA. In addition, their EMA-reported activity levels differed from the sensor data. Participants self-reported higher levels of activity compared to the activity levels calculated by the wearable sensors. This suggests that participants overestimated their activity levels on EMA, or that the activity level cut-points may need to be re-evaluated for the cLBP population. Additionally, sensors placed on different body locations showed varying activity and step counts. The activity counts calculated from the waist ActiGraph and the back sensor from this cohort were lower than the average activity counts in the US adult population. Further research is needed to better quantify these differences for people with cLBP to develop a more comprehensive understanding of the pain experience.