Muscle stretch and theories of contraction

Frog sartorius muscle was loaded with a small cup to which mercury could be added or removed with a motor-driven syringe to achieve dynamic loading cycles. Intermittent stimulation during the loading and unloading cycle very significantly reduced the creep of the resting muscle. Analysis of the data indicates that contraction acts to reset the resting length of the muscle system as well as evoke the contractile response. On the basis of the available evidence, it is suggested that a resetting of the cross linkages between the myosin rods and the actin filaments during contraction is the most plausible explanation of this interaction between the contractile mechanism and the viscoelastic state of the resting muscle.