Superfast tension transients from intact muscle fibres.

We have measured tension transients from tetanically stimulated intact single fibres of the M. lumbricalus and the M. tibialis anterior of the frog. The measurements were carried out between 5.5 and 7 degrees C at a sarcomere length of 2.1 and 3.1 micron with a displacement servo system capable of performing displacements of 50 micron in 40 microseconds. We found a very fast recovery process in the tension transients thus obtained and quantified the speed of the observed recovery process in terms of elasticity and damping. If a ramp-shaped input signal of 150 microseconds duration is applied to the system, the velocity is constant over about 100 microseconds. This property of the system enables us to study the velocity-dependent part of the initial drop in tension in more detail. The first part of the tension transients thus obtained, show three phases: an initial rapid drop in tension, a slower steady decrease in tension and a rapid recovery (30 microseconds).