CONTRACTILE CHANGES ON SKELETAL MUSCLE ASSOCIATED WITH THE MEN STRUAL CYCLE AFTER THE 3-DAY 'DRY' IMMERSION AS MICROGRAVITY SIMU LATION IN WOMEN

Purpose. The study aimed to investigate the changes in muscle architecture (lengths and angles of fascicles) of the female medial gastrocnemius muscle (MG) in vivo and the changes in biomechanical properties of muscles after 3 days of ‘dry’ water immersion (DI) with respect to the menstrual cycle. Methods. Young healthy females (n = 6, age 28.4 ± 1.4 yr, body length 1.7 ± 0.1 m, body weight 60.2 ± 3.8 kg) volunteered to participate in the study. The subjects had a moderate physical activity level and a normal menstrual cycle 26-32 days, (mean 28 days) and did not receive any hormonal treatment. The isometric maximum voluntary contraction (MVC) of the plantar flexor muscles was measured using a isokinetic dynamometer (Biodex, USA) at an ankle angle of 0 °. The subjects performed drop jumps (DJs) from drop heights of 20 (DJ20), 40 (DJ40) and 60 (DJ60) cm on a contact plate. Statistical comparisons of the vertical ground reaction force (vGRF), impulse, moment, power, and work were made between different DJ heights. A real-time B-mode ultrasound system (Edge, USA) and a linear 7.5-MHz electronic transducer with a 60-mm field of view were used to obtain MG images (to measure the fascicle length and angle) at rest and during MVC (100 %). Additional images were taken at 20 and 80 % of MVC at an ankle angle of 0 °. The internal architecture of the MG was determined at ankle angles of -15 ° (dorsiflexion), 0 ° (a neutral anatomical position), and +30 ° (plantarflexion) and a knee angle of 0 °. In each position, longitudinal ultrasound images of the MG were obtained at the proximal level corresponding to 30 % of the distance between the popliteal crease and the center of the lateral malleolus. The images obtained at rest for each ankle position were used to measure, the fiber length (Lf) and pennation angle (Qf) relative to the aponeurosis. The cycle phases considered were menstrual early follicular (when the estradiol concentration is low) and late follicular (when estradiol is elevated). Three sets of experiments (Isokinetic, Jumping, and Architecture) were performed following. The Isokinetic and Jumping experiments were carried out 1 day before the start of DI, as part of as baseline data collection (BDC -1) and the next day after the rise (rise (R); R +1) from the bath. The Architecture experiment was performed on the day of starting the DI exposure (BDC -0) and immediately after the end of DI (R +0; later follicular phase). Results. Significant changes in MVC, muscle architecture, and mechanical properties of the human muscle were observed in the late follicular phase. MVC increased significantly (by approximately 11%) in the late follicular phase. DJ performance in the late follicular phase was better than in the early follicular phase. Conclusion. Changes in female steroid hormones during the menstrual cycle were concluded to increase the muscle strength and to affect the mechanical properties of human muscles in the follicular phase. The finding supports the idea that the hormones influence the regulation of the parameters under study in conditions of unloading of the muscular apparatus.