Kinematics and muscle activities of the lumbar spine during and after working in stooped postures.

Existing biomechanical evidence suggests mechanisms of low back injuries and disorders associated with prolonged stooping. However, no research has tested realistic and more natural stooped work conditions with human subjects in the investigation of the biomechanical responses of the low back in prolonged stooping. The current study was aimed to explore various biomechanical responses of the low back in more realistic and work-related loading and posture conditions of prolonged stooping. Twenty two subjects performed stooped work tasks for 7min with periodic micro-breaks in upright standing, and various measures for assessing biomechanical responses of the low back were obtained before, during and immediately after the stooped work period. Study results found significant increases (p<0.05) in the range of lumbar flexion and myoelectric activation of the low back muscles after the stooped work period. During stooped work, the low back extensor muscles did not show flexion-relaxation. It could be concluded that the natural and unrestricted stooped work conditions produced similar viscoelastic responses of the low back to what more severe stooping conditions with posture restrictions did in previous research, but could be more fatigue-prone due to low but consistent activation of the low back extensor muscles during stooped work activities.