Kolosova O. Modulation ifluences on the Нoffmann reflex in physically untrained and trained humans

The dissertation is devoted to analysis of changes in spinal reflexes dynamics after fatiguing muscle contractions in physically untrained and trained humans. The long-lasting voluntary static contractions of the triceps surae muscle evoked a depression of the soleus H-reflex followed by a subsequent recovery. The presence of two phases of the H-reflex recovery was revealed: the first phase (with a running time of several minutes), associated with the recovery of activity in the groups III and IV afferents; and the second phase (with duration up to a few hours), associated likely with the gradual washing out and neutralization of metabolites that have been accumulated in the muscle during fatiguing contractions. Possible influences on the fatigue-dependent changes of the H-reflex related to action of the spinal inhibitory systems were also analyzed: 1) the segmental inhibition connected with stimulation of the ipsilateral peroneal nerve; 2) the homosynaptic depression evoked by the paired stimulation of the tibial nerve. The H-reflex inhibition due to muscle fatigue as well as to the combined effect of fatigue and homosynaptic postactivation depression in conditions of paired tibial nerve stimulation was shown to be lower in group of people trained for the long-lasting physical activity compared to untrained ones. This might be associated with lower level of metabolites accumulation and higher rate of its utilization in trained persons, which may be related to adaptative changes in the neuromuscular system during exercise. An increase in the H-reflex inhibition intensity under the influence of homosynaptic postactivation depression was revealed, most pronounced in 90 s after a period of fatiguing muscular effort. The H-reflex dynamics under the conditions of the segmental inhibition caused by preceding peroneal nerve stimulation was evaluated during the recovery from fatigue. It was shown that the changes in the test and conditioned H-reflexes were quite similar, whereas these reflexes decreased almost in a proportional manner just after the fatiguing contractions. The existence of a definite separation between the following neuronal pathways might be proposed: 1) the presynaptic inhibition related to the conditioning stimulation of the peroneal nerve; and 2) the direct inhibitory muscle fatigue effects. Gender and age-dependent peculiarities of the parameters obtained in the course of H-reflex study in persons with a high level of adaptation to physical exercise were also analyzed. There were demonstrated differences of both the thresholds and maximal values of the H- and M-responses in the groups of the trained females and males. The maximal amplitudes of the M-responses and the ratios of the maximal amplitudes of the H- and M-responses were shown to be different for groups of the trained adults and young persons. For studying motor control system it has been proposed to take into account the gender and age of the tested people while analyzing the absolute electromyographic indices including basic amplitude parameters of the H-reflex.