In Vivo Evaluation of Medial Gastrocnemius Muscle
The purpose of the current project is to quantify in vivo and noninvasively biomechanical properties of the Medial Gastrocnemius muscle in both stroke survivors and normal subjects. Medial Gastrocnemius is a bi-articular muscle crossing both knee and ankle joints and its properties are dependent on movement at both ankle and knee joints. The architectural properties of the MG are evaluated by using a GE LOGIQ-9 ultrasound machine when both knee and ankle joint positions are changed systematically. Muscle architectures including the pennation angle, fascicle length andmuscle thickness in the MG are measured in vivo and noninvasively. Torque-angle relation as well as architectural measurement as a function of joint angle is established. A programmable electrical stimulator is used to activate the Medial Gastrocnemius (MG) selectively. To overcome the limited field of view, a novel technique, LOGIQview, implemented in the GE LOGIQ-9 ultrasound machine is used to register the muscle images covering the full fiber lengths.
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Illustration of experimental setup
Schematic illustration of electrical stimulation and corresponding torque signals around the ankle joint. Electrical stimulation is used to activate the MG selectively.
Longitudinal ultrasound images of the medial gastrocnemius muscle at rest and under contraction induced by electrical stimulation. MTJ represents musculo-tendon (muscle aponeurosis) junction. α and β represent the posterior and anterior pennation angle respectively. MTJ of MG was identified and treated as a distal reference point. Muscle thickness was then measured 2 cm away and the fascicle lengths were measured around 5 cm from the reference point. Pennation angle measurements were taken at the fascicular insertion in both deep and superficial aponeurosis, namely, the anterior pennation angle and the posterior pennation angle.