Meeting Abstract

S7.8  Tuesday, Jan. 6  Mechanical Behavior of Aponeuroses AZIZI, E*; ROBERTS, TJ; Brown University; Brown University manny_azizi@brown.edu

The elastic structures of many muscles include both an extramuscular free tendon as well as a sheet-like aponeurosis. Free tendons and aponeurosis are structurally similar with collagen fascicles being primarily oriented along the muscles line of action. Unlike free tendons, aponeuroses surround a substantial portion of the muscle belly and may therefore be loaded both parallel (longitudinal) and perpendicular (transverse) to a muscles line of action when contracting muscles bulge to maintain a constant volume. However, little is known about the biaxial strain patterns and mechanical properties of aponeuroses. Here we quantify the mechanical properties of the turkey lateral gastrocnemius aponeurosis in the longitudinal and transverse directions using uniaxial materials tests. We then quantify the pattern of biaxial loading during force production in situ using biplanar video fluoroscopy. We find that the aponeurosis has a significantly higher Young’s modulus in the longitudinal than the transverse direction. Our results also show that aponeuroses can behave as efficient springs in both the longitudinal and transverse directions losing little energy to hysteresis. Results from in situ experiments show that aponeuroses are stretched in both longitudinal and transverse directions during force production and that transverse strains are on average 4 times higher than longitudinal strains. The presence of large transverse strains highlights an important difference between sheet-like aponeuroses and free-tendons. We suggest that biaxial loading potentially functions to alter aponeurosis stiffness dynamically during force production, thereby increasing the tissues capacity for elastic energy storage. Supported by NIH grant AR055295 to TJR and AR054246 to EA.