Changes to 3 D muscle fascicle geometry during contraction

Muscle is a three dimensional (3D) entity with varying shape across the length of the muscle and changes shape during contraction. Changes in muscle shape can influence the orientation of the fascicles within the muscle [1]. Dissection studies examining 3D muscle fascicles architecture have reported regional variations in the fascicle architecture [2]. 2D ultrasound studies have shown that the muscle fascicles are curved, and the curvature depends on the contraction state of the muscle [3]. Muscle modeling studies have predicted 3D curving of the fascicles [4], and dissection studies in human first dorsal interosseous muscle (FDI) [5] and animal muscles [6] have shown 3D helical curvature of fascicles. Previous work on muscle architecture has been mostly in 2D, and a few diffusion tensor MRI and 3D ultrasound studies have quantified the 3D fascicles orientations in passive muscles. 3D fascicle architecture has not been studied during active muscle contractions. The aim of this study was to obtain the map of muscle fascicle orientations and curvatures in human triceps surae during different muscle lengths and contraction states.