Lumbar-pelvic coordination during repetitive lifting of novice and experienced lifters

Abstract

Occurrences of low back disorders are high among individuals working in occupational settings that involve manual material handling tasks, particularly repetitive lifting. This study attempts to better understand the relationship between lumbar-pelvic coordination in repetitive lifting and lower back injury risk by examining differences between inexperienced and experienced lifters. It was hypothesized that experienced lifters would choose a more neutral coordination. Subjects performed repetitive lifting while kinematic and electromyographic (EMG) data was collected. The kinematic data showed that novice subjects approached the limits of their range of motion, during extension while experienced lifters maintained a more neutral lumbar spine during the entire lifting cycle. A second hypothesis was that a more kyphotic lumbar-pelvic coordination pattern preferred by inexperienced lifters would be more energetically efficient due to stretch-shortening dynamics. A computational spine model was also used to determine subjects' erector spinae muscle length during the experiment. EMG data was plotted against muscle length to form average work loops. These work loops were assessed for both the subjects preferred lifting strategy and two strategies trained with biofeedback (kyphotic and neutral). Work loops for the trained neutral lifting strategies encompassed less area, suggesting this style of lifting was more energetically efficient than a more trained kyphotic strategy. Therefore, the second hypothesis was not supported as kyphotic work loops encompassed more area than the other strategies.