This work presents an approach to mathematical description of back surface kinematics. General purpose measurement techniques, based on the last generation of opto-electronic systems for image capture and motion analysis, have been adopted in order to acquire in real-time the 3-D co-ordinates of a suitable grid of passive markers placed on the back surface. A fast, specially-developed bicubic B-spline interpolation algorithm has been then used to increase the spatial resolution of the acquired digital image. This procedure, applied to each acquired frame, has allowed the tracking of the surface movements and the evaluation of the related changes of shape during the execution of some simple motor tasks. A further data processing has completed the quantitative description of the rendered surface (iso-level curves, asymmetries, etc.) in static and dynamic conditions.

The study of the morphological changes induced by movement can be a useful tool both in clinical applications (such as the evaluation of the gibbosity in scoliotic patients and the related plasticity during suitable motor tasks) and in research programmes (such as the analysis of the effects induced by skin elasticity on kinematic measures performed through skin marker systems).