ABSTRACT
Lateral bending of the trunk has been specifically identified as a high risk factor for lower back disorders. However, few studies have presented in vivo kinematic data of the trunk while performing functional lateral bending tasks. Five healthy male subjects performed lateral lifting and lowering tasks under loading condition ranging from light (2kg) to 100% of a maximum (ML) at a controlled velocity. Single lowering tasks were also performed at 125% and 150% of ML. Video based movement analysis was used to determine kinematics of the trunk, pelvis, shoulders and neck in the frontal plane. Centre of pressure (COP) data was also obtained from a force platform on which the subjects stood when performing the lifting and lowering tasks. Kinematics of the trunk revealed a smooth and relatively large change in angular displacement (between 69°to 55°) toward the unloaded side during the lifting phase. Trunk angular displacement significantly decreased with increasing lifting load. The trunk was additionally divided into four segments representing the lower and upper lumbar regions and the lower and upper thoracic regions. The greatest displacement in these segments took place at the upper lumbar and lower thoracic regions (ranging from 29°to 22°and 23°to 17°, respectively) with the least displacement occurring in the lower lumbar and upper thoracic regions (approx. 6° and 5°, respectively). Both the upper lumbar and lower thoracic segments showed significant decreases in angular displacement with increasing load. During the single lowering trials the trunk rotated toward the loaded side with slightly less magnitude to that recorded during the lowering phase of the heaviest lifting and lowering conditions. Angular displacements of the upper lumbar and lower thoracic segments also decreased with increasing load in single lowering. Identified changes in the COP displacement were also correlated to increasing lifting and lowering load. The main findings of this study indicate that it is the central sections of the trunk that have the greatest motion during