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Fig. 3. Single frame ultrasound image of the medial gastrocnemius from one subject.
Three sets of three points (white crosses) were marked on the first frame to
identify the lines of the superficial aponeurosis (top white line), the deep
aponeurosis (bottom white line) and a muscle fascicle (diagonal white line).
The length of the fascicles (lf) is defined by the
intersections of the three lines (white circles). The pennation angle of the
fascicles (
) is the acute angle between the fascicle line and the deep
aponeurosis line. The longitudinal displacement of the fascicle (d)
is used to calculate the length of the tendon (length of the
muscle–tendon unit – d).