Age-related differences do affect postural kinematics and joint kinetics during repetitive lifting

Background: Age is considered a risk factor for manual handling-related injuries and older workers incur higher injury-related costs than younger co-workers. This study investigated the differences between the kinematics and kinetics of repetitive lifting in two groups of handlers of different ages. Methods: Fourteen younger (mean 24.4 yr) and 14 older (mean 47.2 yr) males participated in the study. Participants repetitively lifted a box weighing 13 kg at a frequency of 10 lifts/min for a maximum of 20 min. Postural kinematics (joint and lumbosacral angles and angular velocities) and kinetics (joint moments) were measured throughout the lifting task using motion analysis and ground reaction forces. Muscle fatigue of the erector spinae was assessed using electromyography. Findings: Peak lumbosacral, trunk, hip and knee flexion angles differed significantly between age groups over the duration of the task, as did lumbosacral and trunk angular velocities. The younger group increased peak lumbar flexion by approximately 18% and approached 99% of maximum lumbosacral flexion after 20 min, whereas the older group increased lumbar flexion by 4% and approached 82% maximum flexion. The younger group had a larger increase in peak lumbosacral and trunk angular velocities during extension, which may be related to the increased back muscle fatigue observed among the younger group. Interpretation: Older participants appeared to control the detrimental effects of fatigue associated with repetitive lifting and limit lumbar spine range of motion. The higher rates of musculoskeletal injury among older workers may stem from a complex interaction of manual handling risk factors. (C) 2014 Elsevier Ltd. All rights reserved.