Fig. 2

a Experimental setup overview. Participants lied in supine position comfortably with the knee flexed at 30°. The ankle was passively moved by a continuous passive motion device from 40° plantarflexion to 21.5° dorsiflexion. The probe of an ultrasonic scanner was placed on the thickest part of MG with minimal pressure. Surface electromyogram was monitored in real time (electrodes were attached to the medial gastrocnemius and could not be seen). b A typical shear modulus-angle relationship curve of MG acquired from single measurement trial of 2D-SWE. c The procedure of self-correction and locating the corrected slack angle. Solid line and dash line denote the modulus-angle curve of spastic MG and unaffected MG respectively. The dotted line denotes the corrected modulus-angle curve obtained by subtracting the dash line from the solid line. The solid dot is the intersection of the threshold line calculate by 3-SD criterion and the corrected curve, denoting the location of the corrected slack angle