LOWER EXTREMITY MOTOR IMPAIRMENTS IN AMBULATORY CHRONIC HEMIPARETIC STROKE: EVIDENCE FOR LOWER EXTREMITY WEAKNESS AND ABNORMAL MUSCLE AND JOINT TORQUE COUPLING PATTERNS

摘要

Although global movement abnormalities in the lower extremity post-stroke have been studied, the expression of specific motor impairments such as weakness and abnormal muscle and joint-torque coupling patterns have received less attention. We characterized changes in strength, muscle coactivation and associated joint torque couples in the paretic and non-paretic extremity of 15 participants with chronic post-stroke hemiparesis (age 59.6yrs ± 15.2) compared to 8 age-matched controls. Participants performed isometric maximum torques in hip abduction, adduction, flexion and extension, knee flexion and extension, ankle dorsi- and plantarflexion and submaximal torques in hip extension and ankle plantarflexion. Surface EMGs of 10 lower extremity muscles were measured. Relative weakness (paretic extremity compared to the non-paretic extremity) was measured in post-stroke participants. Differences in EMGs and joint torques associated with maximum voluntary torques were tested using linear mixed effects models. Results indicate significant post-stroke torque weakness in all degrees of freedom except hip extension and adduction, adductor coactivation during extensor tasks, in addition to synergistic muscle coactivation patterns. This was more pronounced in the paretic extremity compared to the non-paretic extremity and to controls. Results also indicated significant inter-joint torque couples during maximum and submaximal hip extension in both extremities of post-stroke participants and in controls only during maximal hip extension. Additionally, significant inter-joint torque couples were identified only in the paretic extremity during ankle plantarflexion. A better understanding of these motor impairments is expected to lead to more effective interventions for post-stroke gait and posture.