Abstract: In the conditions of space flight, maintaining physical performance is one of the important tasks. In space flight, such negative effects as skeletal muscle atrophy, decreased endurance and contractility of muscles, and decreased muscle tone develop. The observed effects occur due to a decrease in the flow of proprioceptive information from muscles and tendons in response to the absence of mechanical loads. To ensure adequate mechanical load, a number of countermeasures means are needed, such as a treadmill, resistive training equipment, etc. The main disadvantage of countermeasures is that the training equipment need much space, while the station volume is limited. One of the promising directions in solving this problem is the use of passive training methods, such as electromyostimulation (EMS). EMS as a method of increasing muscle functionality is used in clinics for the rehabilitation of patients [6] suffering from diseases of the peripheral and/or central nervous system. In the light of these observations, EMS may be an alternative method for maintaining the contractile properties of the human muscular system in conditions of prolonged support unloading. The main purpose of this study was to evaluate the effect of combined EMS on contractile and viscoelastic properties of muscles under conditions of ground-based modeling the physiological effects of weightlessness. 20 healthy males participated in the study, 10 of them made up the control group (30.5 ± 4.3 years) and 10 (33.10 ± 4.3 years) – the experimental one (using combined EMS). A Dry Immersion (DI) model was used to simulate the effects of microgravity [9]. The DI procedure was standard, the duration of exposure was 7 days. EMS training was performed in the form of 2 sessions daily for 7 days of DI. The morning EMS session was conducted for 35-45 minutes on all stimulated muscle groups simultaneously, the evening EMS session was conducted for 10 minutes on each muscle group. The optimal frequency of EMS depends on the type of stimulated muscle group: for postural muscles with a predominance of slow fibers, low-frequency EMS (LF; 25 Hz) has the greatest effect, for muscles with a high content of fast fibers, the most effective is EMS with a high frequency (5 kHz) modulated to 50 Hz (HF). To assess the viscoelastic properties of soft tissues, the MyotonPro surface palpation method (Myoton AS, Estonia) was used. During the measurement, the sensor of the device is pressed into the skin with a slight force (0.18 N) perpendicular to the direction of the muscle fibers of the muscle under study. The sensor of the device outputs three short (15 ms) mechanical pulses of stable strength (0.4 N) with an interval of 1 s. The parameters describing the viscoelastic properties of the muscle are calculated based on their response vibrations. In this study, we analyzed only the transverse stiffness parameter. The tensiomyography method (TMG-BMC Ltd.; Ljubljana, Slovenia) was used to assess the contractile properties of muscles. The amplitude of the muscle response was recorded during an electrically induced isometric contraction using a highly sensitive sensor with a constant elasticity of 0.17 N/mm, which was placed perpendicular to the muscle belly. The studied parameters were the maximum amplitude of the sensor displacement (Dm) and the time to achieve from 10% to 90% displacement of the muscular belly (Tc). The data were analyzed using the ANOVA repeated measurement method (GraphPad Prism, version 9). The most noticeable and stable changes were observed in the medial head of Gastrocnemius muscle. Thus, in the control group, the Dm value increased by 47% (p<0.05) on the first day after DI, while the reverse pattern was observed in the group with EMS. The Dm value decreased by 23% (p<0.05) on the first day after DI. At the same time, muscle stiffness in the control group decreased by 6% (p<0.05) on the first day after DI, whereas in the group with EMS, stiffness did not significantly change. The Tc value in the control group increased by 50% (p<0.05) on the first day after DI, while the Tc in the group with EMS at the same time decreased by 16% (p<0.05). The use of a combined EMS regimen can help to reduce the effect of 7-day support unloading on the contractile and viscoelastic properties of the lower extremities’ muscles.

Cite: Ponomarev I.I. , Saveko A.A. , Bekreneva M.P. , Abu Sheli N.M.A. , Tomilovskaya E.S.
EFFECT OF 7-DAY COURSE OF ELECTROMYOSTIMULATION ON THE CONTRACTILE AND VISCOELASTIC PROPERTIES OF THE MUSCLES OF THE LOWER EXTREMITIES UNDER CONDITIONS OF SUPPORT UNLOADING
43rd Annual the International Society of Gravitational Physiology Meeting 26-31 May 2024