Postural Observation of Shoulder Flexion during Asymmetric Lifting Tasks Xu Xu 1 , Chien-Chi Chang 1 , Gert S. Faber 2 , Idsart Kingma 2 , and Jack T. Dennerlein 3,4 1 Liberty Mutual Research Institute for Safety, 71 Frankland Road, Hopkinton, MA 01748 U.S.A. 2 Institute for Fundamental and Clinical Human Movement Sciences, Faculty of Human Movement Sciences, VU University, Van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands 3 Department of Environmental Health, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115 U.S.A. 4 Department of Orthopaedic Surgery, Brigham and Women’s Hospital, Harvard Medical School, 75 Francis Street Boston, MA 02115 U.S.A. Abstract. This study was to evaluate the observation error of the shoulder flexion angle during an asymmetric lifting task. The results indicated the average absolute estimate error was 14.7 degrees and the correlation coefficient between the measured and estimated shoulder flexion was 0.91. The observation error may be due to the arm abduction. Keywords: Shoulder flexion, Posture observation, Side-view, Lifting tasks. 1 Introduction Shoulder musculoskeletal disorders (MSD) have been a major occupational injury. Some studies found that shoulder joint deviation can lead to shoulder joint injury or discomfort (Holmstrom et al., 1992). One way to monitor awkward shoulder postures is by postural observation. Although postural observation is not as accurate as using laboratory equipment, it is still widely adopted by ergonomists to assess mechanical exposure as it does not require specialized equipment and does not involve strong interference with the normal operations of those being surveyed. A previous study indicated that observers could provide good estimates on shoulder flexion when the arms moved in the sagittal plane (Genaidy et al., 1993). On the other hand, a more recent study indicated that the observation error of shoulder posture was large during lifting tasks (Lu et al., In press). The main objective of this study was to evaluate the observation error of the shoulder flexion angle during an asymmetric lifting task. A lifting task was designed to provide motion tracking system-based direct measurement of shoulder flexion as well as video clips with which the shoulder flexion could be estimated by the raters with a customized program.