Diagnosis of Muscle Diseases at the Molecular Level With a Passive Constitutive Theory for a Single Muscle Fiber

Titins are mainly responsible for passive mechanical properties of single muscle fibers, which, however, can be compromised by the change in molecular structures of titins occurring in some muscle-related diseases. Based on molecular structures of titins within a sarcomere unit, we have developed a constitutive theory for the passive elasticity of single muscle fibers. The theory prediction is in agreement with experiment. With the utilization of the theory, we demonstrate that abnormal structural parameters of titins from patients with chronic obstructive pulmonary disease or muscle atrophy caused by long-term disuse can be extracted. We then suggest that this constitutive theory may facilitate the molecular diagnosis of muscle diseases exhibiting abnormality in the passive elasticity.