ACCURACY AND REPEATABILITY OF LOW-BACK SPINE COMPRESSION FORCE ESTIMATES FROM SELF-REPORTS OF BODY POSTURE DURING LOAD HANDLING

The purpose of this study was to determine whether estimates of peak L (4)/L(5) lumbar spine compression could be accurately and repeatably o btained from participant self-reports of trunk and arm posture. Twenty -seven people participated in two related experiments involving 7 lift ing tasks ranging in complexity. Expt. 1 involved subjects lifting loa ds for one session, whereas Expt. 2 involved repeated testing in two s essions 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 (E xpt. 1) or videotaped (Expt. 2), the joints digitized, and then input into a biomechanical model, resulting in criterion lower back spine co mpression forces. The participants also chose, from a set of diagrams on a questionnaire, the arm, forearm and trunk postures which they fel t most closely matched their actual posture at the heaviest instant. T hese selections were input into a software package which computed rela tive joint coordinates, which, when input into the biomechanical model , resulted in spine compression force estimates corresponding to the s elf-reported postures. No statistical differences (p < 0.05) were foun d in spine compression forces resulting from criterion or self-reporte d postures for men or women, for all tasks in Expt. 1, or between sess ions in Expt. 2. Participants had most difficulty reporting arm postur es, and the most complex tasks resulted in the largest absolute differ ences in spine compression forces resulting from the self-reported and criterion postures. Relevance to industry Considerable time and expen se could be saved if it were possible to rely on workers' reports of t he demands of their jobs using questionnaires. Various physical loadin g variables, for example spine compression force, have been found to b e associated with musculoskeletal discomfort and injury to the low bac k in industrial settings. Accurate and repeatable estimation of low ba ck loading using questionnaires would be a cost-effective alternative to more expensive analysis methods for large-scale studies.