Peculiarities of Afferent Innervation of Antagonist Muscles of the Bilateral Lower Legs during High-Speed Locomotor Movements

The article presents the specifics of intra-, intermuscular, and cross-manifestations of impulse activity of various groups of afferents (Ia, Ib, and II) of the antagonist muscles of the bilateral lower legs when performing high-speed locomotor movements. The study involved 9 male athletes specializing in short-distance running who performed a locomotor test—pushing a passive treadmill belt for 10 seconds at the fastest possible speed. Electromyograms of the antagonist muscles lower legs (m. tibialis anterior, m. gastrocnemius med.) were recorded during running, followed by its processing in the MatLab program and calculation of the impulse activity of primary and secondary afferents using mathematical model based on the prediction of the triggering of muscle spindles. It has been established that high-speed running is a cross intramuscular EMG pattern of tension of the antagonist muscles of the bilateral lower legs with a transition to their relaxation, which depends on the phase of movement. Such muscle innervation in the individual phases of a high-speed running step was manifested by effective intermuscular coordination of the flexor and extensor in the phases of stance and swing of the right leg, pronounced reciprocal relations of homonymous antagonistic muscles of the lower leg in the phases of swing of the right and stance of the left legs. Intramuscular proprioceptive afferentation of the antagonist muscles lower legs of high-speed movement is characterized by the manifestation of strong impulse activity of afferents Ib, moderate afferents II and weak Ia afferents of flexors and extensors of the of symmetrical legs. A phase-dependent modulation of the intermuscular afferentation of the primary and secondary fibers of the flexors and extensors of the bilateral lower legs in the phases of stance and swing of a high-speed running step is shown. The cross-interactions of afferent activity of homologous muscles of the bilateral lower legs in different phases of movement, characteristic of a high-speed running step, have been established. The identified features of intramuscular, intermuscular, and cross-limb afferent activity during running reflect their key role in regulating the inhibitory interneuron network of the spinal cord, which maintains targeted muscle contraction and modulates motor output parameters as a whole. The supposed reflex mechanisms of high-speed locomotor movements are discussed on the basis of well-known phenomena associated with the interaction of various afferent inputs to the spinal cord neuronal apparatus in the system of lower leg antagonist muscles.