Influence of 21-day antiortostatic hypokinesia on the functional state of the musculoskeletal system of human

Abstract

The influence of antiorthostatic hypokinesia with an inclination angle relative to the horizon of -6 degrees for 21 days was used as a ground model of the physiological effects of weightlessness. 10 practically healthy male volunteers (30.7 ± 5.4 years, 78.0 ± 8.5 kg, 179.7 ± 5.3 cm) took part in the experimental study, who successfully passed the medical expert commission of the SSC RF-IMBP RAS, familiarized with the study program and signed a voluntary informed consent to participate in the study. The state of the musculoskeletal system was assessed according to the results of speed-strength testing on an isokinetic dynamometer before hypokinesia and on the 3rd day after its completion. Staying in conditions of 21-day anti-orthostatic hypokinesia with a body inclination angle of –6° relative to the horizon, as a model of the physiological effects of weightlessness, leads to changes in the functional state of the musculoskeletal lower limbs which manifests itself during speed-strength testing after hypokinesia by a decrease in maximum voluntary force (MPF) of the knee joint extensor muscles from 9 to 15% compared with the base level. The decrease in MPF did not depend on a change in the force gradient, which reflects the ability to exert greater force in the shortest possible time. This indicated that the decrease in the MPF level after hypokinesia was mainly due to a change in the activity of slow motor units. At the same time, we assume that exposure to hypokinesia did not cause a significant change in the activity of fast motor units. This is confirmed by the results of the analysis of the electromyographic activity of the extensor muscles of the knee joint during testing on an isokinetic dynamometer. Also, after hypokinesia, the possibility of using muscle potential significantly decreased - the physiological cost of work increased with a decrease in strength indicators.