NAIAD-2020: Characteristics of Motor Evoked Potentials After 3-Day Exposure to Dry Immersion in Women

As female astronauts participate in space flight more and more frequently, there is a demand for research on how the female body adapts to the microgravity environment. In particular, there is very little research on how the neuromuscular system reacts to gravitational unloading in women. We aimed to estimate changes in motor evoked potentials (MEPs) in the lower leg muscles in women after 3-day exposure to Dry Immersion (DI), which is one of the most widely used ground models of microgravity. Six healthy female volunteers (mean age 30.17 ± 5.5 years) with a natural menstrual cycle participated in this experiment. MEPs were recorded from the gastrocnemius and soleus muscles twice before DI, on the day of DI completion, and 3 days after DI, during the recovery period. To evoke motor responses, transcranial and trans-spinal magnetic stimulation was applied. We showed that changes in MEP characteristics after DI exposure were different depending on the stimulation site, but were similar for both muscles. For trans-spinal stimulation, MEP thresholds decreased compared to baseline values, and amplitudes, on the contrary, increased, resembling the phenomenon of hypogravitational hyperreflexia. This finding is in line with data observed in other experiments on both male and female participants. MEPs to transcranial stimulation had an opposing dynamic, which may have resulted from the small group size and large inter-subject variability, or from hormonal fluctuations during the menstrual cycle. Central motor conduction time remained unchanged, suggesting that pyramidal tract conductibility was not affected by DI exposure. More research is needed to explore the underlying mechanisms.

Mechano-Immunomodulation in Space: Mechanisms Involving Microgravity-Induced Changes in T Cells

Of the most prevalent issues surrounding long-term spaceflight, the sustainability of human life and the maintenance of homeostasis in an extreme environment are of utmost concern. It has been observed that the human immune system is dysregulated in space as a result of gravitational unloading at the cellular level, leading to potential complications in astronaut health. A plethora of studies demonstrate intracellular changes that occur due to microgravity; however, these ultimately fall short of identifying the underlying mechanisms and dysfunctions that cause such changes. This comprehensive review covers the changes in human adaptive immunity due to microgravity. Specifically, there is a focus on uncovering the gravisensitive steps in T cell signaling pathways. Changes in gravitational force may lead to interrupted immune signaling cascades at specific junctions, particularly membrane and surface receptor-proximal molecules. Holistically studying the interplay of signaling with morphological changes in cytoskeleton and other cell components may yield answers to what in the T cell specifically experiences the consequences of microgravity. Fully understanding the nature of this problem is essential in order to develop proper countermeasures before long-term space flight is conducted.

Molecular Mechanisms of Muscle Tone Impairment under Conditions of Real and Simulated Space Flight

Kozlovskaya et al. [1] and Grigoriev et al. [2] showed that enormous loss of muscle stiffness (atonia) develops in humans under true (space flight) and simulated microgravity conditions as early as after the first days of exposure. This phenomenon is attributed to the inactivation of slow motor units and called reflectory atonia. However, a lot of evidence indicating that even isolated muscle or a single fiber possesses substantial stiffness was published at the end of the 20th century. This intrinsic stiffness is determined by the active component, i.e. the ability to form actin-myosin cross-bridges during muscle stretch and contraction, as well as by cytoskeletal and extracellular matrix proteins, capable of resisting muscle stretch. The main facts on intrinsic muscle stiffness under conditions of gravitational unloading are considered in this review. The data obtained in studies of humans under dry immersion and rodent hindlimb suspension is analyzed. The results and hypotheses regarding reduced probability of cross-bridge formation in an atrophying muscle due to increased interfilament spacing are described. The evidence of cytoskeletal protein (titin, nebulin, etc.) degradation during gravitational unloading is also discussed. The possible mechanisms underlying structural changes in skeletal muscle collagen and its role in reducing intrinsic muscle stiffness are presented. The molecular mechanisms of changes in intrinsic stiffness during space flight and simulated microgravity are reviewed.

Intermittent short-arm centrifugation is a partially effective countermeasure against upright balance deterioration following 60-day head-down tilt bed rest

This study investigated whether artificial gravity (AG), induced by short-radius centrifugation, mitigated deterioration in standing balance and anticipatory postural adjustments (APAs) of trunk muscles following 60-day head-down tilt bed rest. Twenty-four participants were allocated to one of three groups: control group (N=8); 30 minutes continuous AG daily (N=8); intermittent 6x5 minutes AG daily (N=8). Before and immediately after bed rest, standing balance was assessed in four conditions: eyes open and closed on both stable and foam surfaces. Measures including sway path, root-mean-square, and peak sway velocity, sway area, sway frequency power, and sway density curve were extracted from the centre of pressure displacement. APAs were assessed during rapid arm movements using intramuscular or surface electromyography electrodes of the rectus abdominis, obliquus externus and internus abdominis, transversus abdominis, erector spinae at L1, L2, L3, and L4 vertebral levels, and deep lumbar multifidus muscles. The relative latency between the EMG onset of the deltoid and each of the trunk muscles was calculated. All three groups had poorer balance performance in most of the parameters (all P<0.05) and delayed APAs of the trunk muscles following bed rest (all P<0.05). Sway path and sway velocity were deteriorated, and sway frequency power was less in those who received intermittent AG than in the control group (all P<0.05), particularly in conditions with reduced proprioceptive feedback. These data highlight the potential of intermittent AG to mitigate deterioration of some aspects of postural control induced by gravitational unloading, but no protective effects on trunk muscle responses were observed.

Impact of Aquafitness Training on Physical Condition of Early Adulthood Women

Background. The physical benefits of fitness for middle-aged women are well-known. Unlike the usual training sessions, aquafitness occupies a special place among the types of health-related exercise training. Its health-enhancing effect results from the activation of the body's functional systems, the gravitational unloading of the musculoskeletal system, high energy expenditures, and overall body hardening effect. The objective of this study was to evaluate the health-enhancing effects of an aquafitness program on the functional indicators and physical fitness of early adulthood women. Materials and methods. Theoretical analysis and generalization of scientific and methodological literature, anthropometric techniques, pedagogical methods, and methods of mathematical statistics were used. The functional status of the body was assessed with the indices characterizing the function of the cardiorespiratory system, which are commonly used. The study was conducted at the Sport Life fitness club, Chernivtsi. The study involved 48 women aged 21-31 with an average age of 26.3 years. The subjects took part in a six-month aquafitness program consisting of 60-min sessions, three times a week. The program was developed by the authors and included aquatic stretching, body shaping and bodybuilding exercise, aquadance, aquatic gymnastics, and aqua tae-bo. Results. After participation in the exercise program: vital capacity increased from 45.96±4.69 to 48.88±0.68; strength index increased from 35.80±1.07 to 43.26±0.71; Robinson's index increased from 85.72±12.34 to 89.63±10.11; Shtange test increased from 30.28±10.32 to 37.78±12.34; Hench test changed from 16.48±4.24 to 25.19±4.58; Kerdo index decreased from 5.23±0.74 to 0.88±0.38; and Rufier's test decreased from 12.21±4.26 to 8.03±2.14. The assessment of somatic health of the women showed a significant improvement (p<0.05). Positive changes in the autonomic system were detected. Conclusion. The developed aquafitness program can be an effective tool for health improvement and body weight management in early adulthood women.

The Role of Long-Term Head-Down Bed Rest in Understanding Inter-Individual Variation in Response to the Spaceflight Environment: A Perspective Review

Exposure to the spaceflight environment results in profound multi-system physiological adaptations in which there appears to be substantial inter-individual variability (IV) between crewmembers. However, performance of countermeasure exercise renders it impossible to separate the effects of the spaceflight environment alone from those associated with exercise, whilst differences in exercise programs, spaceflight operations constraints, and environmental factors further complicate the interpretation of IV. In contrast, long-term head-down bed rest (HDBR) studies isolate (by means of a control group) the effects of mechanical unloading from those associated with countermeasures and control many of the factors that may contribute to IV. In this perspective, we review the available evidence of IV in response to the spaceflight environment and discuss factors that complicate its interpretation. We present individual data from two 60-d HDBR studies that demonstrate that, despite the highly standardized experimental conditions, marked quantitative differences still exist in the response of the cardiorespiratory and musculoskeletal systems between individuals. We also discuss the statistical concept of “true” and “false” individual differences and its potential application to HDBR data. We contend that it is currently not possible to evaluate IV in response to the spaceflight environment and countermeasure exercise. However, with highly standardized experimental conditions and the presence of a control group, HDBR is suitable for the investigation of IV in the physiological responses to gravitational unloading and countermeasures. Such investigations may provide valuable insights into the potential role of IV in adaptations to the spaceflight environment and the effectiveness of current and future countermeasures.