Accuracy and repeatability of low back spine compression force estimates from self-reports of body posture during load handling

Abstract

The purpose of this study was to determine whether estimates of peak L 4/L 5 lumbar spine compression could be accurately and repeatably obtained from participant self-reports of trunk and arm posture. Twenty-seven people participated in two related experiments involving 7 lifting tasks ranging in complexity. Expt. 1 involved subjects lifting loads for one session, whereas Expt. 2 involved repeated testing in two sessions separated by 1 week. Following practice with the lifting tasks, participants held the load in the posture they felt they were in at the heaviest instant of each task. These postures were photographed (Expt. 1) or videotaped (Expt. 2), the joints digitized, and then input into a biomechanical model, resulting in criterion lower back spine compression forces. The participants also chose. from a set of diagrams on a questionnaire, the arm, forearm and trunk postures which they felt most closely matched their actual posture at the heaviest instant. These selections were input into a software package which computed relative joint coordinates, which, when input into the biomechanical model, resulted in spine compression force estimates corresponding to the self-reported postures. No statistical differences ( p < 0.05) were found in spine compression forces resulting from criterion or self-reported postures for men or women, for all tasks in Expt. 1, or between sessions in Expt. 2. Participants had most difficulty reporting arm postures, and the most complex tasks resulted in the largest absolute differences in spine compression forces resulting from the self-reported and criterion postures.