Effect of supraspinal influences on the manifestation of presynaptic inhibition Ia afferents in different types of muscle contraction in humans

Abstract

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.

Keywords

• presynaptic inhibition
• h-reflex
• concentric contraction
• eccentric contraction
• isometric contraction
• jendrassik maneuver
• maximum voluntary contraction (mvc)