Functional Activity of Reciprocal Inhibition of α-Motor Neurons of Antagonistic Muscles in Different Types of Muscle Contractions of Submaximal and Maximal Force

Abstract

INTRODUCTION: Currently, the results of investigation of different types of spinal inhibition in isometric voluntary contraction of muscles have been published. There are separate reports devoted to the role of recurrent and presynaptic inhibition in the regulation of isometric and anisometric voluntary contractions of submaximal and maximal strength. AIM: To evaluate the effect of the type and strength of muscle contraction with and without performing Jendrassik maneuver on the manifestation of reciprocal inhibition of -motor neurons of antagonistic muscles of the lower leg. MATERIALS AND METHODS: The study involved 8 healthy men aged 2022 years. Reciprocal inhibition was evaluated by suppression of the amplitude of testing H-reflex of m. soleus in conditioning stimulation of n. peroneus profundus, and of testing stimulation of n. tibialis with 3 msec interval between stimuli. Reciprocal inhibition was recorded in concentric, eccentric and isometric contractions with 50% and 100% of maximal voluntary contraction (MVC) with and without Jendrassic maneuver. RESULTS: In performing concentric, eccentric and isometric contractions of lower leg muscles with increase in strength from 50% to 100% of MVC, the activity of reciprocal inhibition decreased. Reciprocal inhibition was most evident in concentric contraction with 50% of MVC strength, less evident in eccentric contraction and was lowest in isometric contraction. With the maximal strength, reciprocal inhibition was most expressed in isometric contraction, less expressed in concentric contraction and was weakest in eccentric contraction. With Jendrassik maneuver, reduction of reciprocal inhibition was more expressed in different types of MVCs in comparison with parameters obtained with 50% of MVC. Using Jendrassic maneuver with 50% and 100% of MVC effort, strongest reciprocal inhibition was recorded in isometric contraction, weaker inhibition in concentric contraction and weakest in eccentric contraction. The effect of Jendrassik maneuver was manifested by weakening of reciprocal inhibition in concentric and eccentric contraction of submaximal force, and by its enhancement in isometric contraction. CONCLUSION: Variability of manifestation of reciprocal inhibition of -motor neurons of antagonistic muscles of lower leg in different types of muscle contractions of submaximal and maximal strength is associated with the fact that the pool of segmental motor neurons of m. soleus is controlled not only by a wide spectrum of excitatory cortico- and reticulospinal influences, but also by other kinds of inhibition, thus providing coordinated motor actions.