Abstract
Analysis of the early tension responses after abrupt step changes in the length of isometrically contracting [rabbit] skeletal muscle shows that the magnitude of the recovery tension (T2) and the time dependence of this process at various step displacements give a good correlation with the behavior expected for a helix-coil transition in the subfragment-2 (S-2) region of myosin. The instantaneous tension response (to T1) after the step change in length appears to have its origin in compliance within the coil region of S-2, which is formed through helix melting at the moment of force generation.