The time course of full lumbar flexion under a prolonged flexion moment, lasting 20 min, was documented in 27 male and 20 female subjects. Peak flexion increased by 5.5° over the 20 min. The flexion-creep data was fitted with a first-order step input response having a time constant of 9.4 min. Maximum flexion was also documented over the recovery phase, lasting 30 min, indicating that subjects regained approximately 50% of their resting joint stiffness within 2 min of resuming relaxed lordosis, although full recovery took longer than the flexion-creep, indicating the presence of viscoelastic hysteresis. For this reason it may be prudent to advise those who experience prolonged full flexion postures (as might a seated warehouse shipper/receiver, gardener, or construction worker) to stand and walk for a few minutes prior to performing demanding manual exertions. Indeed, temporary joint flexion laxity, following a bout of full flexion, may increase the risk of hyperflexion injury to certain tissues.
Copyright © 1992. Published by Elsevier Ltd.