Muscle force strategies for poststroke hemiparetic patients during gait.

BACKGROUND AND OBJECTIVE: Individuals who survive a stroke often display considerable gait impairments that occur in part due to inadequate muscle force production. This study aimed to investigate lower limb muscle forces in poststroke patients during walking. METHODS: Kinematics, kinetics, and electromyographic (EMG) measurements were performed on nine poststroke and healthy individuals walking at natural speed in a cross-sectional study. Recorded parameters were used in an EMG-driven model to estimate the forces exerted by the muscles around the knee and ankle joints during the stance (braking and propulsion) and swing phases. RESULTS: For hemiparetic patients, in comparison to healthy controls, the paretic side exhibited (i) lower forces generated by plantar-flexors and quadriceps respectively during the braking and propulsion phases, but (ii) higher knee-flexors forces during the propulsion phase. Regarding the non-paretic side, it displayed (i) higher forces generated by knee-flexors and quadriceps (only for the propulsion phase) forces during the stance phase, and (iii) higher plantar-flexors forces during the swing phase, in comparison to controls. CONCLUSION: Reduced forces exerted by the plantar-flexors and the knee-extensors along with increased force generated by the knee-flexors on the paretic side give possible explanation for hemiparetic gait abnormalities. Increased muscle forces exerted by the non-paretic side might be a compensatory strategy to better support body weight and properly adjust the center of mass forward.

Co-contraction around the knee and the ankle joints during post-stroke gait.

BACKGROUND: Impairments resulting from hemiparetic stroke lead to persistent difficulties with walking. Abnormal co-contraction patterns of lower limb muscles might be a compensatory mechanism to deal with its resulting gait impairments. AIM: The aim of this study was to assess muscle co-contraction obtained from muscle moments in chronic hemiparetic patients presenting a stiff-knee gait (SKG) during walking. DESIGN: Cross-sectional study. SETTING: Clinical movement analysis laboratory in a health center and a community hospital. POPULATION: Twelve hemiparetic patients 6 months' post-stroke (mean±SD age 49.3±12.5) walking with a SKG and twelve healthy adults (mean±SD age 23.5±7.7). METHODS: Hemiparetic patients walked at their natural gait speed while healthy adults walked at their natural and slow gait speed. Spatiotemporal, kinetic and kinematic gait parameters were determined for both lower limbs. Co-Contraction Index at the knee and the ankle was calculated from muscle moments estimated using an EMG-driven model during the first (DS1) and second (DS2) double support and the single support (SS) phases and the swing phase (SW). RESULTS: The results revealed that chronic stroke patients have reduced ankle co-contraction and increased knee co-contraction during DS1 phase, increased ankle co-contraction during DS2 phase and increased knee co-contraction during SW phase on the paretic side. On the non-paretic side, muscle co-contraction was higher at the knee during SS phase. CONCLUSIONS: Increased co-contraction during walking in both the paretic and the non-paretic side, in patients with hemiparesis exhibiting a SKG, might be an adaptive strategy to increase walking stability, as it may be related to spasticity, but also could result in a high metabolic cost. CLINICAL REHABILITATION IMPACT: The information obtained in this study may be used to support rehabilitation programs focusing on the selectivity of movement control such as strength or power training.