Exploring the effects of task design on the flexion-relaxation phenomenon in the lumbar spine during repetitive...

Repetitive forward flexion of the lumbar spine can result in creep deformation which can disrupt load sharing between active and passive tissues. Lumbar spine kinematics and lumbar erector spinae (LES) electromyography were used to measure flexion relaxation (FR) angle changes across two lifting conditions matched for cumulative external load (Condition 1: 75 lifts of 13 kg load, Condition 2: 150 lifts of 6.5 kg load). Males showed increases in FR onset angle in response to the low load, high repetition condition, while females displayed increases in these metrics in the high load, low repetition condition. This work suggests that task design of a repetitive lifting task, and creep accumulation in the lumbar spine may be sex specific and future work should look to consider both task parameters, as well as worker demographics when designing and evaluating repetitive lifting task.