Using sitting as a component of job rotation strategies: Are lifting/lowering kinetics and kinematics altered following prolonged sitting Samuel J. Howarth, Tyson A.C. Beach, Adam J. Pearson, Jack P. Callaghan * Faculty of Applied Health Sciences, Department of Kinesiology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada article info Article history: Received 12 July 2007 Accepted 27 October 2008 Keywords: Low-back loading Shear Gender differences abstract 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  during the lifting/lowering exertions following the first hour of sitting which consequently led to a reduction of approximately 50 N 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 conse- quence 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. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Alternating between two working scenarios (job rotation) has been suggested as a method for altering exposure to detrimental postures, forces and/or repetitiveness in the workplace. The underlying principle of job rotation is that rotating between two or more different tasks in a rotation scheme is thought to alter the load distribution as well as reduce total exposure to harmful postures. For example, the low-back pain reporting index was altered upon implementation of task rotation (Frazer et al., 2003). However, it may be possible that prolonged exposures to one scenario may have adverse effects on the manner in which a subsequent task is conducted which could lead to increased potential for injury. In certain occupational settings, workers are required to perform manual lifting/lowering exertions following periods of prolonged sitting (e.g., warehouse attendants, truck drivers and bus drivers). Both sitting for extended durations and repetitive lifting have been acknowledged as risk factors for developing low-back pain (Lyons, 2002; Pope et al., 2002). However, reviews on the causes of low-back pain in the workplace address sitting and lifting independently (Pope et al., 2002). Due to changes that could arise in the mechanical and sensory-motor functioning of low-back tissues in exposures akin to prolonged sitting (Solomonow et al., 2003), it has been hypothesized that individuals exposed to the aforementioned occupational scenario may be at increased risk of sustaining a low-back injury (McGill and Brown, 1992; Beach et al., 2005). Recently, Shin and Mirka (2007) hypothesized that reduced force generating capacity of elongated erector muscles in the spine during prolonged full flexion combined with an increase in vertebral joint laxity reduces the safety margin that would increase the susceptibility to generating low-back injury during bouts of lifting immediately following the flexion exposure. To our knowledge, no studies have been con- ducted to examine whether low-back kinematics or kinematics during lifting would change following periods of prolonged sitting. A seated posture imposes flexion upon the lumbar spine often greater than 50% of a person’s maximal range of motion in flexion (Callaghan and McGill, 2001; Dunk and Callaghan, 2005; Gregory et al., 2006). Sustaining a fully flexed lumbar and trunk posture for prolonged periods of time has been linked to viscoelastic creep of the lumped passive tissues (McGill and Brown, 1992) which may also occur at submaximally flexed lumbar postures such as those * Corresponding author. Tel.: þ1 519 888 4567x37080; fax: þ1 519 746 6776/885 0470. E-mail address: callagha@healthy.uwaterloo.ca (J.P. Callaghan). Contents lists available at ScienceDirect Applied Ergonomics journal homepage: www.elsevier.com/locate/apergo 0003-6870/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.apergo.2008.10.006 Applied Ergonomics 40 (2009) 433–439