Individualized Contractile Ankle Joint Muscular Properties in Healthy and Post-Stroke Subjects

Abstract: This study investigated the contractile properties of the plantar-and dorsi-flexor muscles controlling the ankle joint. The purpose of this study was to investigate how the muscle strength and muscle architecture change after stroke, and how the muscle strength and architecture are correlated. 13 typically developed (TD) subjects and 8 post-stroke (PS) individuals participated in this study where they performed maximal isometric tests (MVC) at 4 angles and isokinetic tests at 2 velocities. Torque-angle and torque-angular velocity relations were created to examine the muscle group strength. Third order polynomial and rectangular hyperbola were used to fit the torque-angle and torque-angular velocity relations, respectively. In addition, a maximum isometric torque and an optimal angle were reported for the healthy and stroke survivors. Ultrasonography system was used to study the muscle architecture at rest and maximal voluntary isometric conditions in the healthy and post-stroke groups. Fascicle length, muscle thickness and pennation angle of the medial gastrocnemius (MG) and tibialis anterior (TA) muscles were measured and compared between the two tested groups. Second order polynomial was used to study the correlation between the muscle strength and muscle architecture at MVC condition. A reduced range of motion and decreased maximal isometric torque were reported in the PS group. In addition, shorter fascicle lengths and smaller muscle thickness were obtained at rest and maximal voluntary contraction states in the stroke survivors compared to the healthy group. Pennation angle increased in the maximal voluntary isometric state compared to the rest condition. Decreased pennation angle was found in the MG, but it was increased in TA at the MVC state in the PS group compared to the healthy group. In the MG muscle, a positive correlation was found between the muscle strength with fascicle length and with muscle thickness in the healthy and post-stroke groups, but negative correlation was found with the pennationa angle in the two groups. In the TA muscle, positive correlation was found between muscle strength and fascicle length and negative correlation with the pennation angle in the TD and PS groups. However, negative correlation was obtained between muscle strength and muscle thickness in the TD group and no clear correlation in the PS group.