Working in flexed torso postures increases the risk of occupationally related low-back disorders. These postures apply strain to spinal tissues that cause temporary disturbances in neuromuscular control of trunk muscles. Existing evidence reveals that there are residual effects on spine biomechanics following exposure to flexed postures. Recovery from these disturbances may be incomplete upon initiation of subsequent tasks thereby causing an accumulation of neuromuscular disturbance. In other words, muscle recruitment, spinal load and spinal stability during a given flexion task is influenced by previous tasks and will influence subsequent tasks. However, the role of work-task design on these disturbances remains unknown. Neuromuscular disturbance will be recorded by quantifying changes in: 1) trunk muscle co-contraction, 2) para spinal reflex response, 3) active trunk stiffness, 4) spinal load, and 5) spinal stability. An exposure-response relationship will be characterized in Specific Aim 1 to test the hypotheses that duration of static flexion is associated with progressive increases in neuromuscular disturbance and that task load increases the disturbance rate. We will quantify changes in co-contraction, stiffness, reflex, spinal load and stability recorded before and after periods of static trunk flexion by means of established methods and models.
Specific Aim 2 will record neuromuscular behavior before and after exposure to flexion postures to test the hypothesis that flexion angle and exposure-rate influence the severity and rate of neuromuscular disturbance. Rate of recovery of neuromuscular behavior following static flexion tasks will also be recorded in Specific Aims 1 & 2 to gain insight into the effects of work-rest scheduling of flexion tasks.
Specific Aims 3 and 4 will test the hypotheses that neuromuscular disturbance can accumulate across repeated static flexion tasks and repetitive dynamic lifting respectively. We will investigate how disturbance severity is influenced by flexion duration, peak flexion angle and lift rate. Finally, we will test the hypothesis that these disturbances can influence the dynamic control of spinal stability. The proposed study will investigate how workplace factors influence the severity and time-course of neuromuscular disturbance (including spinal load and stability). Results will guide future studies and/or epidemiologic investigations regarding the mechanism of cumulative risk from flexed working postures. ? ? ?
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