Using sitting as a component of job rotation strategies: are lifting/lowering kinetics and kinematics altered following prolonged sitting.

Workers are often required to perform manual materials handling tasks immediately following periods of prolonged sitting either as a secondary job component of as different tasks in a job rotation strategy. The goal of this investigation was to determine if changes to low-back kinetics and/or kinematics occurred during repetitive lifting/lowering exertions following extended seated exposures. Upper body kinematics, lumbar spine flexion angle, pelvic orientation and bilateral muscle activity from the external abdominal obliques and lumbar erector spinae were recorded for 8 males and 8 females while they alternated between sessions of repetitive lifting/lowering and prolonged sitting. Upper body kinematics were used as inputs to a linked segment model to compute low-back flexion/extension moments, compression, and shear. Peak lumbar flexion was reduced by 1.8 degrees during the lifting/lowering exertions following the first hour of sitting which consequently led to a reduction of approximately 50N in the reaction anteroposterior shear forces. Sitting postures were consistent with previously reported data. The reduced shear loads during repetitive lift/lower exertions following prolonged sitting may be a consequence of alterations in passive tissue properties which could alter the risk of low-back injury, although future research is required to examine the biomechanical significance of this finding. Changes to both kinematics and kinetics were minimal suggesting that using prolonged sitting as a component of a task series in job rotation does not alter the risk present when combined with repetitive lifting tasks.