TORQUE ACTION OF 2-JOINT MUSCLES IN THE SWING PERIOD OF STIFF-LEGGED GAIT - A FORWARD DYNAMIC-MODEL ANALYSIS

Stiff-legged gait, characterized by limited knee flexion during the sw ing period, is a common consequence of upper motor neuron injury. The purpose of this investigation was to determine whether the rectus femo ris and hamstrings muscles (which act at both the hip and knee) contri bute to stiff-legged gait if active during the swing period of the gai t cycle. Ten subjects with unilateral stiff-legged gait due to stroke were evaluated. Swing period free gait data were obtained. A biomechan ical model of the affected limb was developed for each subject. Muscle and tendon lengths were scaled to individual subjects while constant nominal values for maximum muscle forces were used for all subjects. T orque driven forward dynamic simulations were employed to determine th e sensitivity of swing period maximum knee flexion angle to changes in hip and knee torques. Combined torque and muscle driven simulations w ere used to access the action of specific two-joint muscles. Both hip flexion torque and knee extension torque were found to influence knee angle, but knee angle was more sensitive to changes in torque at the k nee joint. The actions of the rectus femoris and long hamstrings are m ost marked at the knee, although their action at the hip opposes their action at the knee. Rectus femoris activity during early swing acts t o limit knee flexion and contributes to stiff-legged gait. Long hamstr ing activity in early swing contributes to knee flexion. (C) 1998 Else vier Science Ltd. All rights reserved.