Muscle history, fusimotor activity and the human stretch reflex

Abstract

1. The previous history of contraction and length changes of a muscle influences the size of the stretch reflex and H reflex. Here we ask, is this dependence due to changes in mechanical properties of extrafusal fibres, intrafusal fibres of spindles, or both? 2. The soleus muscle of human subjects was conditioned using either a voluntary contraction or a contraction evoked by low-strength electrical stimulation, in the range 0-25% of maximum. Following conditioning, reflexes were increased by more than twofold above the no-contraction value by a voluntary contraction of 5% of maximum, or more, but not by electrical stimulation which presumably did not contract the intrafusal fibres of spindl..