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It is known, transcutaneous electrical spinal cord stimulation (tESCS) in the T11-T12 level of the thoracic vertebrae increases the power capabilities of the leg agonist muscles. One of the inhibition spinal mechanisms that protects skeletal muscles from excessive force is non-reciprocal inhibition. Taking into account the biological role of non-reciprocal inhibition, the aim of the study was to research the effect of long-term tESCS on expression of non-reciprocal inhibition of soleus muscle α-motorneurons in humans at rest and when holding a weak static force. Materials and methods: the study involved 22 healthy male subjects aged 27 to 35 years. Non-reciprocal inhibition of α-motorneurons was recorded during the 20-minute tESCS in the T11-T12 level of the thoracic vertebrae at rest, in combination with arbitrary muscular effort (5% of MVC) and after its impact. Results: TESCS at rest resulted in the weakening of non-reciprocal inhibition within 20 minutes of exposure and 10 minutes after the end of stimulation. TESCS in combination with arbitrary muscular effort in 5% of the MVC increases the activity of non-reciprocal inhibition for 20 minutes of stimulation and 10 minutes after its end. The proposed physiological mechanisms underlying the effect of long-term tESCS on expression of non-reciprocal inhibition are discussed.

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Relevance. Тhe biological role of presynaptic inhibition is to regulate excessive skeletal muscle tone, which prevents the execution of arbitrary muscle contractions. In the modern literature, there is information devoted mainly to the study of various types of spinal inhibition in the isometric type of contraction. The aim: determining the role of supraspinal influences from brain stem structures on the activity of presynaptic inhibition when performing various types and sizes of muscle contractions in humans. Materials and methods: 20-22 year-old healthy men (n=6) took part in the research. Presynaptic inhibition was registered at rest; at rest in combination with the performance of Jendrassik maneuver; when performing concentric, eccentric, isometric contractions of 50 % and 100 % of the individual maximum without and against the background of Jendrassik maneuver. Results: During the execution of concentric, eccentric and isometric contractions of different sizes, the severity of presynaptic inhibition decreases in comparison with rest, both without taking Jendrassik maneuver, and against the background of its execution. With an increase in the strength of concentric, eccentric, and isometric contractions from 50 % to 100 % of the individual maximum, the severity of presynaptic inhibition progressively decreased under the same experimental conditions. Without taking Jendrassik maneuver, the greatest severity of presynaptic inhibition was observed with concentric and isometric contractions of 50 % and 100 % of the MVC, and against the background of taking Jendrassik maneuver - with an isometric type of reduction of 50 % and 100 % of the MVC. Conclusion. Supraspinal descending effects caused by the Jendrassik maneuver modulate the state of presynaptic inhibition Ia of the afferents of the flexor muscle of the foot, depending on the type and strength of muscle contraction.

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