Thixotropy: the effect of stimulation in frog muscle.

Recent reports have shown that the stiffness of relaxed frog muscle is not a fixed property, but is dependent on the previous history of movement (Lakie & Robson, 1988a). Passive movement decreases stiffness; when the muscle is subsequently allowed to rest it returns at a progressively declining rate to a level of stiffness that is close to its original value (Lakie & Robson, 1988b). We now report that the stiffness of relaxed muscle is also affected by prior tetanic electrical stimulation under isometric conditions. The effect of electrical stimulation is similar to passive movement in that both produce a temporary decrease in stiffness.