Descriptive modelling of fascicle curvature in gastrocnemius muscles

Introduction: Power loss of skeletal muscles remains a major negative side effect of longterm exposure to weightlessness. Besides muscle atrophy also changes in muscle architecture and mechanics have significant force reducing impact. In muscle research it is well established to analyse changes in fascicle’s length and pennation angle. Several studies reported that fascicles sometimes curve. This bending could be another mechanical parameter that influences the muscle’s force generation. It has been shown that muscle fascicle curvature increases with increasing contraction level (CL) and decreasing muscle-tendon-complex (MTC) length. The analyses in these studies were done with limited examination windows concerning contraction state, MTC length and/or intramuscular position of ultrasound imaging. Additionally, fascicle curving has, to the best of our knowledge, not yet been produced by in-silico muscle models, which suggests that the mechanisms are poorly understood. With this study we aimed to investigate the phenomenon of fascicle arching in gastrocnemius muscles in order to develop hypotheses about its fundamental mechanism and to reproduce the curving with a theoretical mesh-type muscle model.