Measuring postural activity in people with chronic low back pain

Background: The objective measurement of free-living physical activity may facilitate the rehabilitation of people with chronic low back pain (CLBP). Objective: This study was designed to investigate the validity of a novel monitor which purports to measure physical activity. Methods: Ten participants with CLBP (9 female, 1 male; age 51 ± 10 years; BMI 27 ± 5 kg.m^{-2}) wearing an activPAL™ activity monitor, were videoed performing a range of everyday tasks in a semi-constrained environment. From the video recordings the activity involved in the tasks was visually classified (criterion method) into four postures: lying/sitting; upright (standing and walking); standing; and walking. This provided a second-by-second recording of movement and posture. Observational data were compared to the activity monitor output for the same four postures. The accuracy of the monitor in measuring step count and cadence was also compared to visual observation. Results: Overall agreement between the monitor and observation was 97%, with overall sensitivity and positive predictive values ranging from 92% to 99%. The 95% limits of agreement for step count and cadence was <1%. Conclusion: The activPAL™ activity monitor is a valid device for measuring postural physical activity, step count and cadence in people with CLBP in a semi-constrained environment.