Transmission phenomena and early tension recovery in skinned muscle fibres of the frog.

Tension responses due to small rapid length changes completed in 50 microseconds were obtained from segments with different length of single fibres of the ileofibularis muscle of the frog. The very early parts of the responses varied with segment length. A simulation of the early parts of the response was carried out by means of a linear model in which the fibre is regarded as a rod of infinitesimally small segments containing undamped elasticity, damped elasticity and mass in series. In the simulation corrections were included for the effects caused by the viscosity and density of the surrounding fluid and for the force transducer characteristics. The results indicate the presence of a very rapid component in the fast recovery with a time constant of 5-15 microseconds. The undamped elasticity of the activated fibres corrected for their passive properties was such that a sudden shortening corresponding to 2.6 nm/half sarcomere would reduce active tension to zero.