POST-TETANIC POTENTIATION OF MYOTATIC REFLEXES IN MAN

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Abstract
In an attempt to demonstrate in man that the monosynaptic reflex is potentiated by tetanization it was found that the H-reflex, simultaneous reciprocal inhibition and the mechanically evoked stretch reflex (Achilles and patellar reflexes) can also be potentiated. During complete relaxation, H-reflexes were found only in the calf muscles but a slight or moderate voluntary contraction of other muscles could change the late deflections making them indistinguishable from typical H-reflexes. Post-tetanic potentiation of more than 100% was shown in the present study. This is probably analogous to the potentiation of the monosynaptic reflex in animals which is attributed to increased pre-synaptic action due to changes in afferent terminal fibers or in synaptic boutons. Suppression of H-reflexes was often seen during the first seconds after tetanus. When the tetanic stimulus had a frequency greater than 200/sec and a duration longer than 30 seconds there was a marked depression of the M-waves due not only to a presynaptic potentiation but also a release from the blocking effect of the antidromic motor discharge.

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