Intramuscular anatomy may obscure correlations between collagen content and passive muscle stiffness

While collagen is believed to be a major passive load bearing structure in muscle, previous work reports a very weak correlation between muscle collagen content and passive stiffness [1,2]. This may result from a lack of appreciation of intramuscular anatomical variations among muscle fibers and connective tissue structures. This study demonstrates that collagen content varies significantly between and within muscles and that these variations are driven by the intramuscular connective tissue. This information is being for prediction of whole muscle passive mechanical properties.