Multi-segment trunk kinematics during locomotion and elementary exercises.

BACKGROUND: Motion of human trunk segments in healthy subjects during activities of daily living has been described either with oversimplified models or with cumbersome techniques of isolated anatomical complex. This study describes multi-segmental trunk motion based on a new technique which is a compromise between technical limitations, implied with the experiments, and clinical relevance. METHODS: The thorax segment was tracked by the optimal spatial matching of four thoracic markers. The separate bi-dimensional shoulder line rotations and translations with respect to the thorax were calculated by markers on the two acromions. Spine motion was characterised by a 5-link-segment model from additional four skin markers, in the anatomical reference frame based on four pelvic spine markers. These 14 markers were tracked in 10 healthy subjects and one clinical case during static upright posture, chair rising-sitting, step up-and-down and level walking, and also during elementary flexion and extension, lateral bending, and axial rotation movements of the entire trunk. FINDINGS: Intra-subject repeatability over ten repetitions was found to be high for most of the measurements, with average standard deviations of less than 1.8° for all planar rotations at the spine, and less smaller than 1mm for shoulder translations. Large motion, albeit with different patterns, was found in all subjects, also revealing interesting couplings over the three anatomical planes. INTERPRETATION: Considerable subject-specific motion occurs at each of these different trunk segments in all three anatomical planes, in simple exercises and in motor tasks of daily living. Measurements taken with the present new trunk model in pathological subjects shall reveal corresponding patterns and ranges of motion in abnormal conditions.