[Dynamics of the efferent regulation of muscle contraction. Analysis of transition processes: frequency of efferent stimulation--muscle length].

Transition processes of the length changes were studied in the ankle extensors of anesthetized cats. The processes were evoked under isotonical conditions by step changes in frequency of distribution stimulation of the efferents supplying these muscles. The system dynamics was essentially nonlinear because the time constants of the processes were dependent on amplitudes and sign of the input signal. The time constants abruptly decreased when the sign of the length changes alternated from minus to plus and continuously decreased when amplitude of the transition process rose in the absolute value. The time constants for the transition processes were 1.15 +/- 0.09 s for soleus shortening and 0.40 +/- 0.07 s for its lengthening. The same parameters in fast muscles were 0.51 +/- 0.085 for shortening and 0.21 +/- 0.04 s for lengthening. These time constants are very close to the parameters of the transition processes: external load-muscles length. The observed properties of the muscles are discussed for their functional significance.