Movement pre-history-dependent aspects of formation of the elongation trajectories of an active muscle

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Trajectories of elongation of an active muscle were studied on the m. soleus of anesthetized cats under conditions of distributed stimulation of efferent fibers and servo-controlled external loading. At different time Intervals after cessation of a high-amplitude unloading the muscle was subjected to a low-amplitude trapezoid testing loading. At applications of the test loading immediately after the conditioning linear unloading or with intervals shorter than 2 sec, the muscle maintained a significantly higher stiffness, as compared with that at longer intervals between the conditioning and testing influences; in the latter situation a decrease in the shortening rate was observed simultaneously with application of the testing loading. At short intervals after unloading, the phase of a dynamic “post-pulling” was practically absent in the muscle response, and just at the moment of fixation of the loading (within the trapezium plateau) the muscle length became rather strongly stabilized with subsequent manifestation of dynamic components, which increased with a further increase in the delay. The short-range stiffness regularly decreased with an increase in the interval between unloading cessation and testing influence, while the amplitude of muscle stretching under the Influence of the test loading increased. Thus, active shortening of the muscle can to a certain extent modify both its dynamic properties and the pattern of its response to the external stretching.

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