Tension responses of frog skeletal muscle to ramp and step length changes.

Tension responses to ramp shortening of varying speed in whole muscle or single fibres from the plateau of an isometric tetanus, revealed at least two distinct phases. There was a fast initial drop in tension followed by a change of slope and a definite inflexion on the tension record. As the velocity of the imposed length change was increased, the inflexion point appeared at a lower tension. Similar inflexions were not observed during ramp releases to an elastic band or a segment of semitendinosus tendon. The tension records obtained with moderately fast ramp length changes to contracting muscle reflect the T1 and T2 phases of the tension transients.