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Efferent responses to twitch tests used in identifying human muscle afferents
J T Inglis1, L R Wilson, S C Gandevia
1Faculty of Applied Health Science, Department of Physical Therapy, Elborn College, University of Western Ontario, London, Canada.
Abstract:
The response of a muscle afferent to the mechanical stimulus produced by a twitch contraction of the receptor-bearing muscle is an important test for differentiating between muscle spindle endings and Golgi tendon organs. The present study demonstrates that active alpha-motor axons can behave in a similar manner to spindle afferents, presumably responding not to the mechanical event per se, but reflexly to the change in afferent discharge created by the mechanical event. alpha-Motor axons were unequivocally identified during microneurography using spike-triggered averages of EMG. Caution is required when the twitch test is utilized to assist in the classification of muscle afferents during an intentional or unintentional voluntary contraction.