Coordination between the Whole Body and the Stepping Movement During Gait Initiation in Parkinson’s Disease

Abstract

In normal subjects, the gait initiation mechanisms have been previously studied by performing multiparametric analyses relying on kinematic, dynamic and EMG recordings (Carlsoo, 1966; Breniere et al., 1981; Burleigh et al., 1994; Elble et al., 1994). The gait initiation process can be described as the succession of a postural phase and a subsequent stepping phase. The initial motor command is presumed to act on the distal leg muscles, then leading to an initial event, that is the backward shift of the center of foot pressure (CP), which commonly occurs with any type of forward oriented whole body movement (Cretina and Frigo, 1991). The postural phase starts with the onset of this backward CP shift, prior to the forward propulsion of the whole body center of gravity (CG). This makes it possible for the stepping movement to be performed by the « leading leg », and the velocity of the CG forward shift at the end of the postural phase contributes to the scaling of the first step length. During the postural phase, the body weight is also transferred laterally onto the other leg (« supporting » leg). The simultaneous forward and lateral CG shifts thus constitute a preparatory postural adjustment, which is coordinated with the stepping movement onset in order to avoid the loss of the body’s equilibrium.