Muscle stretch used as conditioning stimulus for assessing a reciprocal inhibition
Pérot, C.; Mora, I.; Goubel, F.
Electromyography and Clinical Neurophysiology 32(7-8): 331-339
1992
ISSN/ISBN: 0301-150X PMID: 1526213 Document Number: 388148
The disynaptic Ia-.alpha. inhibition between the tibialis anterior and the soleus muscles is now well known. This neuronal organization has been established thanks to the analysis of the Hoffman reflex (H reflex) changes following an electrical stimulation of the antagonist muscle nerve. In some cases, anatomical constraints impede the use of this classical technique for assessing a reciprocal Ia inhibition between muscles. Furthermore, an electrical stimulus solicits the primary spindle afferents in conditions which are very different from their natural stimulus: the muscle stretch. Thus we have undertaken to analyze the changes of a soleus H reflex following a rapid stretch of the ankle dorsiflexors and therefore of their prime-mover: the tibialis anterior. The mechanical perturbations were imposed with a strong initial acceleration and a limited angular displacement thanks to an original device including electromagnet and spring. This technique, derivated from the quick release technique, was applied on relaxed muscles to avoid a co-contraction phenomenon. 45 to 50 ms after the initiation of the mechanical perturbation an early reflex response was observed on the stretched tibialis anterior. The area of this first reflex response was related to the initial acceleration of the passive dorsiflexion. Several arguments are presented in favor of the myotatic origin of this reflex component. The passive dorsiflexion used as a conditioning stimulus led to a strong and longlasting inhibition of the test soleus H reflex. The early inhibition of the soleus H reflex was observed only about 18 ms after the conditioning stimulus. Owing to the difference in latency between a stretch response and a H response (about 15 ms for the soleus) this interstimuli interval seems adequat to be representative of the disynaptic inhibitor pathway between the tibialis anterior Ia afferents (and the Ia afferents of the other dorsiflexors) and the soleus .alpha. motoneurons. Furthermore the reinforcement of the soleus H reflex inhibition with the intensity of the conditioning stimulus was easily observed despite the relaxed state of the tested muscles. In conclusion, these experiments demonstrate that a rapid stretch which mobilizes a muscular group in conditions near from natural movements can be proposed in order to reveal a reciprocal inhibition phenomenon.