Are There Cumulative Changes in Lumbar Spine Passive Stiffness Throughout a Week of Prolonged Seated Work?

This study assessed daily and weekly changes in spine mechanical properties, specifically range of motion and passive stiffness, in those with and without sitting-induced low back pain to determine if time-dependent changes in mechanical properties were related to pain development in prolonged sitting. Over 1 week, 20 participants performed their seated office work and attended 5 laboratory sessions (Monday morning and evening, Tuesday morning, Friday evening, and the following Monday morning) to measure lumbar spine stiffness in passive flexion. Accelerometers measured seated lumbar flexion-extension each workday. In the morning and evening, participants provided low back pain ratings and performed maximum voluntary flexion. Statistical tests compared over time and between pain statuses (nonpain < 10 of 100 mm). There were increases in maximum flexion from morning to evening (2.0°; P = .003) and decreases in angular breakpoints on Monday evening and Tuesday morning (4.6% and 6.8% of passive flexion; P ≥ .056). Classification of seated spine flexion-extension into the transition and high stiffness zones of the passive curve (ie, moderate-high flexion) revealed that sitting strained the posterior passive tissues, likely contributing to the changes in range of motion and stiffness. Nevertheless, alterations in spine properties did not accumulate throughout the week and were not different by pain status.