RECOVERY OF STRETCH REFLEX RESPONSES FOLLOWING MECHANICAL STIMULATION

The recovery behaviour of mechanically evoked stretch responses was in vestigated. Stimuli which promoted identical dorsiflexing movements ar ound the ankle joint were applied to ten subjects in two positions, se ated and upright. The experimental sets comprised single as well as do uble dorsiflexing displacements. In the latter the stimuli were elicit ed for durations of either 100, 200 or 400 ms. Stretch responses follo wing the first displacements were related to the stretch velocity but not to the amplitude. The responses of the plantar flexors following t he second mechanical dorsiflexion were reduced with respect to the del ay time between the first and second displacement. In addition, the ma gnitudes of these responses depended on the functional task: the stret ch responses recovered much faster in the standing position when the t riceps surae muscle was only slightly activated, whereas in the relaxe d sitting position the reflexes remained suppressed. Both reciprocal i nhibition, as well as the time course of the reformation of intrafusal cross-bridge links, may help to explain the depression of the monosyn aptic stretch reflex.