Passive mechanical properties of mammalian muscle are not affected by the intracellular titin protein

The purpose of this study was to directly compare the passive moduli of single muscle fibers and fiber bundles from both frog and mouse muscles. This study demonstrated that the passive elastic tensile load born by frog fibers is almost exclusively born intracellularly by the muscle fibers themselves rather than by the ECM, while ECM bears the majority of the load in mouse fiber bundles. Based on these results, these data demonstrate that intracellular titin would bear only 1-2% of whole muscle tension in mammalian muscle, highly unlikely to be functionally significant.