OPTIMIZATION AND SMOOTHING TECHNIQUES IN MOVEMENT ANALYSIS

This paper deals with accurate estimation of the degrees of freedom (D OF) of a body segment, starting from the trajectories of clusters of m arkers acquired with a suitable measurement system. The most commonly employed estimation procedures involve two sequential steps, a traject ory smoothing algorithm and a DOF reconstruction routine. Three optimi zed smoothing and reconstruction schemes are described, analyzed and t ested and their performances are compared with each other and with tho se of a more traditional technique which contains no optimization crit eria. All three schemes include an iterative, weighted-least-squares D OF reconstruction routine and a self-tuning, zero-phase-shift, 4th-ord er Butterworth filter. Both routines are extensively described and val idated on the basis of numerically-simulated marker trajectories. Test results, analyzed on a statistical basis, show that the use of an opt imization routine provides a visible improvement in DOF reconstruction . This performance has also been confirmed using stereophotogrammetric data collected on a subject wearing an external fracture fixation dev ice which provides reference values for the bone DOF. Angular DOF esti mated applying the optimized method to skin technical clusters are muc h closer to the reference values than the non-optimized values. Smooth ing of data further improves the reconstruction accuracy while a far l ess crucial role is played by the order in which smoothing and reconst ruction routines are applied.