Between-day fluctuations in seated low back pain are linked to seated spine movements

• Seated spine movements were related to between-day fluctuations in low back pain • On days with higher pain ratings, participants exhibited larger spine movements • Spine movements were also less frequent on higher pain days • Seated spine postures were not different between days with different pain ratings There is considerable variability in low back pain reporting during seated exposures, where pain ratings vary day-to-day, and previous pain does not consistently translate to future pain. The current study assessed within-subject differences in seated activities and spine kinematics between days with minimum and maximum pain ratings, with the goal of understanding the relationship between spine kinematic strategies and sitting-related low back pain. Over one workweek, twenty young and back-healthy participants completed their usual seated office work at their own workstation. Sitting and standing/stepping time were measured from a thigh-worn activity monitor, and spine kinematics were measured from two accelerometers on the low back. Low back pain ratings were collected on a 100 mm visual analog scale before and after each workday. Nine participants exhibited mild differences in pain between two days (≥5 mm) and time-varying activities and kinematics on their Minimum and Maximum pain days were assessed. Additionally, data from the eleven participants with stable pain responses were evaluated in an extended Bland-Altman to characterize normal daily variability. On their higher pain days, participants exhibited larger but less frequent spine movements, with no differences in activities or seated spine postures. Although the mean differences in movement amplitude (0.4°-1.7°) and timing (4-32 seconds) were small, the differences consistently exceeded the mean difference between days for the participants with stable pain responses. Thorax reclination also increased throughout the day on both pain days. Collectively, responses to low back pain in sitting appear to be linked to strategies in lumbar spine micromovements and reclining on the seatback.