The primary purpose of this paper was to compare the effect of reversing the direction of step initiation in Parkinson's disease. Forward (FDS) and backward (BDS) oriented stepping initiation analyses were conducted on combined kinematic and kinetic data recorded on Parkinsonian patients (PD) and healthy age-matched subjects. Two successive phases were examined: a postural phase from T1 (onset of the center of pressure [CP] displacement) to T2 (onset of the malleolus displacement), which was followed by a stepping phase from T2 to T3 (end of the malleolus displacement; i.e., the end of the step). In healthy subjects, the duration of the postural phase remained unchanged regardless of the direction in which the step was initiated. The stepping phase duration and the first step length were reduced in BDS in comparison with FDS. In both tasks, the absolute value of the horizontal force in sagittal plane (Fx) remained unchanged. The maximal velocity of the iliac crest marker (estimated whole body center of gravity [CG]) in the sagittal plane (Vmax CG) remained within the same range regardless of direction of stepping. In Parkinsonian patients, the duration of the postural phase was markedly prolonged in both tasks in comparison with healthy subjects. The mean duration of stepping phase was approximately the same as in normal subjects, but the first step length was considerably reduced, as were horizontal force (Fx) and Vmax CG. This impairment, which was due to a decrease in the propulsive forces, was significantly more pronounced in BDS that in FDS.
The authors can be reached at DPM-CNRS 31, chemin J. Aiguier, 13402 Marseille cedex 20, France. Additionally, N.Gantchev is with Institute of Biophysics, Acad. G. Bontchev str., bl. 21, 1113 Sofia, Bulgaria, and F. Viallet is with Service de Neurologic, CH du pays d' Aix, 13616, Aix en Provence, France.