Figure 2. Pennation angle measurements.

The diagram shown represents a sagittal muscle sonograph of gastrocnemii. The curved line between aponeuroses represents a fascicle. Lines 1 and 2 divide the area between aponeuroses into three horizontal bands of equal dimensions. Lines S₁ and S₂ pass through the intersection point between the fascicle and the lines 1 and 2, respectively, and the insertion point of the fascicle onto the superficial and deep aponeurosis of the muscle. a and b are digitized pennation angles on the superficial and deep aponeurosis, respectively. The vertical bands A, B and C represent the three different areas analysed to establish whether architecture was constant along the image.