New Methodology and Preliminary Data in the Charac-terization of the Muscle Tendon Junction of Mammalian Muscle Tissues

The muscle-tendon junction (MTJ) has been a point of inquiry and confusion for at least the past 30 years. Attempts to model its behavior under load are based on datacollection methods that utilize high-level microscopic information to determine the stress-strain response. This is further compounded by the fact that the MTJ cannot be well modeled as a simple homogeneous material because of the biochemical engagement and compliance of each of the tissue types involved in the formation of this complex, multi-tissue type, junction. Here we present a method and preliminary data to correlate high level stress-strain information gathered from microscopic evaluation of rodent flexor muscles with molecular strain derived from x-ray diffraction data (XRD). The strain data obtained using the described method show that the tendon (collagen) region of the MTJ is significantly more resistant to stretch application than the muscle component. This is the expected response from the tissue, as the muscle absorbs most strain, while the tendon carries mechanical load with minimal elasticity. Our data reveals additional information, showcasing the molecular state in addition to high-level tissue behavior seen while under tensile load. These data correlate with the microscopic observations. We also describe, for the first time, a method to determine the transitional boundary of the MTJ, from the belly of the muscle to the true tendon, using XRD.