COMBINED STUDY OF SEGMENTAL MOTIONS AND THE MOTION OF THE BODY CENTER OF MASS DURING WALKING: NORMATIVE DATA AND APPLICATIONS TO FUNCTIONAL DIAGNOSIS AND TREATMENT IN REHABILITATION MEDICINE.

In the present Thesis, walking was analyzed at various velocities in healthy participants, adults and children, on a split-belt treadmill mounted on 3D force sensors. Each belt can rotate at a different velocity, thus inducing artificial claudication. Conventional kinematic (optoelectronic) and surface EMG recordings from several lower limbs muscles were conducted. This experimental setting allowed to investigate both the motion of the body system as a whole (represented by its centre of mass, CoM) and the power provided by lower limb muscles (mostly, the plantar flexors). Various branches of an experimental campaign demonstrated that: a) a lateral shrinking of the CoM path is demonstrated with increasing age in children from 5 to 13 years. The lateral CoM oscillation/velocity function looks like a promising index of neural maturation. b) In adults, the 3D trajectory of the CoM implies a sharp U-turn (radius of curvature as small as 2 mm) at the beginning of the left-to-right (or vice-versa) oscillation, implying demanding muscular coordination. This curvature looks like a promising index of balance during walking. c) The claudication induced by “split” walking causes temporal asymmetries (“escape limp”) analogous to those found in pathologic claudication (shorter stance time, on the faster belt) but opposite spatial and dynamic asymmetries (longer posterior step and higher pantar flexors’ power, on the faster belt). d) The average velocity of the CoM on split-belt treadmills is different from the mean velocity between the belts. This velocity depends on the time spent by the point of application of the resulting ground reaction force on either belt. This implies that errors were made in the Literature, comparing split walking with tied walking at the mean velocity between the two belts. e) A representative unilaterally paretic patient has been analyzed to give an idea of the feasibility and the potential usefulness of the combined segmental and CoM analysis on split-belt treadmills. Overall, the series of experiments paves the way to a more soundly based analysis of pathologic gaits.