Title: Exploring the effects of lifting load and frequency on the flexion-relaxation response in the lumbar spine during repetitive lifting
Supervisors: Dr. Kayla Fewster
Committee members: Dr. Jean-Sébastien Blouin, Dr. Michael Hunt
Abstract: Repetitive and prolonged static forward flexion of the lumbar spine are frequently involved with occupations like manual materials handling on assembly lines, or seated desk work in an office. Repetitive lumbar flexion superseding 80% of healthy range of motion, has been widely accepted as a risk factor for low back disorders (LBD) and notably low back pain (LBP). Evidence suggests that passive tissues in the lumbar spine are quintessential to maintaining healthy spine function, coordination, and preventing injury. At near-maximal lumbar flexion, the passive tissues in the lumbar spine produce sufficient tension and counter-moment to the upper body such that the lumbar erector spinae musculature enter a period of myoelectric silence. This neuromechanical event is termed flexion-relaxation (FR).
With this phenomenon in mind, substantial efforts have been made to delineate the factors involved in the alteration of passive tissue mechanics in the lumbar spine and how this may relate to changes in injury risk during repetitive lifting tasks. During and following bouts of repetitive lifting, the lumbar angle at which FR onset occurs has been shown to increase, characterizing a change in the load-sharing of the active and passive tissues of the lumbar spine. High lifting load and lift frequency are both factors that have been shown to cause changes in passive tissue mechanics during repetitive lifting tasks. These factors along with cumulative load have also been found to all be strong predictive factors in the development of LBP. The vast majority of repetitive lifting literature evaluating the effect of lifting load has neglected the effect of cumulative load and consequently have failed to control for it across lifting tasks.
In the proposed thesis, we will be investigating the effect of lifting load and lifting frequency on the angle of FR onset during 2 cumulative load-matched lifting task conditions. Condition 1 involves 75 cycles of lifting 13 kg at a rate of 1 lift per minute while condition 2 involves 150 cycles of lifting 6.5 kg at a rate of 2 lifts per minute. The goal of this thesis is to evaluate changes in FR between two cumulative load-matched tasks to determine if the parameters in which task is performed expose workers to differing or elevated injury risk. The findings from this study would help determine if the parameters of a lifting task effect lumbar spine injury risk in a cumulative load-matched task. This would further inform occupational health and safety regulatory bodies thereby preventing occupational low back injury.