Bio class

  Force-Length Relationship      Due to the presence of titin, muscles are innately elastic. Skeletal muscles are attached to bones via tendons that maintain the muscle under a constant level of stretch called the resting length. If this attachment was removed, for example if the bicep was detached from the scapula or radius, the muscle would shorten in length.  Simply put,  the tension generated in skeletal muscle is a function of the magnitude of overlap between actin and myosin myofilaments. Force-Velocity Relationship      The force-velocity relationship in muscle relates the speed at which a muscle changes length with the force of this contraction and the resultant power output (force x velocity = power). The force generated by a muscle depends on the number of actin and myosin cross-bridges formed; a larger number of cross-bridges results in a larger amount of force. 

     The cross-bridge theory of muscle contraction states how force is produced, and how the filaments actin and myosin are moved relative to each other to produce muscle shortening. In the cross-bridge theory, sidepieces that are fixed in a regular pattern on the myosin filament (cross-bridges) are thought to undergo cyclic attachment and detachment to specific binding sites on the actin filament. During an attachment/detachment cycle, the cross-bridge head is thought to undergo a rotation and so pull the actin filament relative to the myosin.  one cross-bridge cycle is thought to occur with the energy gained from the hydrolysis of one adenosine triphosphate (ATP).