Stretch forces in skeletal muscle myofibrils and myosin molecules

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Muscle contraction is a basic function of life. The standard theory used to explain the mechanisms of muscle contraction is known as the cross-bridge theory, and was proposed half a century ago. However, several aspects of muscle contraction are still poorly understood. Among these aspects, the high forces produced during stretch of an activated muscle fiber cannot be readily explained by the cross-bridge theory. The goal of this proposal is to investigate the mechanisms behind stretch forces, and its association with the molecular basis of muscle contraction. We propose to use novel and accurate methods of measurement that include single myofibrils (sub-cellular components of muscle fibers) and single molecule mechanics to test hypotheses that have been raised to explain stretch forces. These hypotheses are associated with the role of contractile proteins and passive elements inside muscle fibers during contraction. Stretch forces are important not only to understand the basic mechanisms of contraction, but also several aspects of the everyday life, like stretch-induced muscle damage, and force potentiation during eccentric contractions.