When skeletal muscle fibres shorten, they must increase in their transverse dimensions in order to maintain a constant volume.\nIn pennate muscle, this transverse expansion results in the fibres rotating to greater pennation angle, with a consequent reduction\nin their contractile velocity in a process known as gearing. Understanding the nature and extent of this transverse expansion is\nnecessary to understand the mechanisms driving the changes in internal geometry of whole muscles during contraction. Current\nmethodologies allow the fascicle lengths, orientations, and curvatures to be quantified, but not the transverse expansion. The purpose\nof this study was to develop and validate techniques for quantifying transverse strain in skeletalmuscle fascicles during contraction\nfrom B-mode ultrasound images. Images were acquired from the medial and lateral gastrocnemii during cyclic contractions,\nenhanced using multiscale vessel enhancement filtering and the spatial frequencies resolved using 2D discrete Fourier transforms.\nThe frequency information was resolved into the fascicle orientations that were validated against manually digitized values. The\ntransverse fascicle strains were calculated from their wavelengths within the images. These methods showed that the transverse\nstrain increases while the longitudinal fascicle length decreases; however, the extent of these strains was smaller than expected.
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