Authors: V Michel R K Y Chong
Publish Date: 2004/05/27
Volume: 158, Issue: 3, Pages: 356-365
Abstract
We used the framework of motor program adaptability to examine how unilateral aboveknee AK or belowknee BK amputee subjects organize the global and local biomechanical processes of generation of the propulsive forces during gait initiation to overcome the segmental and neuromuscular asymmetry The organization of the global biomechanical process refers to the kinematics behavior of the couple center of foot pressure CoP and center of mass CoM the organization of the local biomechanical process refers to the propulsive forces generated by the prosthetic or intact limb during the anticipatory postural adjustment phase and the step execution phase Specifically we examined i the strategy to regulate the progression velocity ie to maintain it comparably when the leading limb changed from the prosthetic limb to the intact limb and ii the strategy to modulate the progression velocity ie to increase it when gait was initiated with the prosthetic limb vs intact limb The kinematics of the CoM and CoP in the amputees showed the same global biomechanical organization that is typically observed in ablebodied subjects ie the production of the forward disequilibrium torque was obtained by a backward shift of the CoP followed by a forward acceleration of the CoM However gait initiation was achieved by using a different local strategy depending on which limb was used to initiate the step For the regulation of the CoM progression velocity when the gait was initiated with the intact limb the slope of the progression velocity during the anticipatory postural adjustment phase APA was steeper and lasted longer the step execution duration was shorter and the variation of the CoM speed was lower In other words to regulate the speed of progression the amputee subjects controlled the spatial and temporal parameters of the propulsive forces In the modulation of the CoM progression velocity when the gait was initiated with the intact limb the amputees controlled only the intensity of the propulsive forces during both the APA and step execution phases In contrast when the gait was initiated with the prosthetic limb the modulation resulted mainly from the propulsive forces generated during the step execution phase These different strategies are discussed in terms of the subject’s capacity to adapt the motor program for gait initiation to new constraints
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