Altered gearing in medial gastrocnemius muscle of chronic stroke survivors

The purpose of this study is to understand variable gearing in medial gastrocnemius (MG) muscle of chronic stroke survivors, as estimated from the “fascicle gear ratio.” Five stroke survivors performed isometric plantarflexions at different ankle joint angles. During each contraction, ankle torque and ultrasound images were recorded simultaneously. Regression analysis was performed with gearing (muscle shortening velocity/fascicle shortening velocity) as a function of torque level, in order to compare variable gearing in non-paretic and paretic MG muscle. We found that gear ratio in non-paretic muscle decreased with increasing torque level, whereas variable gearing was lost in paretic muscle. This result may provide better understanding of a potential impact of altered muscle architecture and material properties on impaired muscle performance after stroke.