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NASA NTRS2023

The Effects of Space Flight and Microgravity Exposure on Female Astronaut Health and Performance

Over the past half century, our understanding of the physiological effects of space exploration and microgravity exposure have improved immensely. Microgravity causes incredible changes to the human body that increase risk of injury upon return to Earth and lunar/planetary egress scenarios. This is due to deconditioning of the cardiovascular and skeletal muscle systems that reduce aerobic capacity and muscular strength. With upcoming exploration class missions, such as NASA’s Artemis lunar exploration program which aims to send the first female astronaut to the lunar surface by 2030, as well as a long-term goal of Martian exploration, maintaining astronaut health during extended-duration space flight is critical for achieving mission objectives. However, our understanding of these physiological implications due to microgravity are based primarily on flight studies of male astronauts and 1g bed rest analog study participants, with few investigations focusing specifically on females. Innate physiologic differences in endocrine signaling and reproductive function impact sex-dependent responses to various health conditions, treatments, and environmental factors in nearly every system in the body. Therefore, to assume comparable alterations in females in response to microgravity exposure may be inappropriate and consequentially, could lead to lasting impacts on female astronaut health and impact mission success. Moreover, differences in sex hormones may also influence the regulation of cardiovascular control during egress activity after space flight-induced deconditioning and blood volume loss (i.e., risk for orthostatic intolerance). Other potential physiological systems and factors related to musculoskeletal health and aerobic capacity that warrant investigation with respect to microgravity include endocrine/reproductive function, vascular control, bone mineral density/microarchitecture, and soft-tissue health. The purpose of this investigation is two-fold: 1) to summarize the data available from space flight and simulated bed rest analog exposures to begin addressing these gaps in knowledge regarding impacts to female astronaut health, and 2) to describe differences in demographic health characteristics, injury prevalence, and aerobic capacity and muscular strength in NASA female and male astronauts. Female astronauts make up 50% of Artemis-specific astronaut corps and the extent to which microgravity exposure impacts female cardiovascular and musculoskeletal health, and whether these alterations are consistent with their male counterparts, is inconclusive. With the growing inclusion of female astronauts in the NASA space program and the increased duration of missions beyond low Earth orbit, a greater understanding of the sex-specific adaptation to space travel will help determine the development of appropriate countermeasures for minimizing risk and maintaining health of all astronauts.

Female Astronaut↗
NASA NTRSDate not supplied

The Effects of Space Flight and Microgravity Exposure on Female Astronaut Health and Performance

Over the past half century, our understanding of the physiological effects of space exploration and microgravity exposure have improved immensely. Microgravity causes incredible changes to the human body that increase risk of injury upon return to Earth and lunar/planetary egress scenarios. This is due to deconditioning of the cardiovascular and skeletal muscle systems that reduce aerobic capacity and muscular strength. With upcoming exploration class missions, such as NASA’s Artemis lunar exploration program which aims to send the first female astronaut to the lunar surface by 2030, as well as a long-term goal of Martian exploration, maintaining astronaut health during extended-duration space flight is critical for achieving mission objectives. However, our understanding of these physiological implications due to microgravity are based primarily on flight studies of male astronauts and 1g bed rest analog study participants, with few investigations focusing specifically on females. Innate physiologic differences in endocrine signaling and reproductive function impact sex-dependent responses to various health conditions, treatments, and environmental factors in nearly every system in the body. Therefore, to assume comparable alterations in females in response to microgravity exposure may be inappropriate and consequentially, could lead to lasting impacts on female astronaut health and impact mission success. Moreover, differences in sex hormones may also influence the regulation of cardiovascular control during egress activity after space flight-induced deconditioning and blood volume loss (i.e., risk for orthostatic intolerance). Other potential physiological systems and factors related to musculoskeletal health and aerobic capacity that warrant investigation with respect to microgravity include endocrine/reproductive function, vascular control, bone mineral density/microarchitecture, and soft-tissue health. The purpose of this investigation is two-fold: 1) to summarize the data available from space flight and simulated bed rest analog exposures to begin addressing these gaps in knowledge regarding impacts to female astronaut health, and 2) to describe differences in demographic health characteristics, injury prevalence, and aerobic capacity and muscular strength in NASA female and male astronauts. Female astronauts make up 50% of Artemis-specific astronaut corps and the extent to which microgravity exposure impacts female cardiovascular and musculoskeletal health, and whether these alterations are consistent with their male counterparts, is inconclusive. With the growing inclusion of female astronauts in the NASA space program and the increased duration of missions beyond low Earth orbit, a greater understanding of the sex-specific adaptation to space travel will help determine the development of appropriate countermeasures for minimizing risk and maintaining health of all astronauts.

Female Astronaut↗
NASA NTRS1999

Alterations in Skeletal Muscle Function with Microgravity, and the Protective Effects of High Resistance Isometric and Isotonic Exercise

Exposure to microgravity or models designed to mimic the unloaded condition, such as bed rest in humans and hindlimb unloading (HU) in rats leads to skeletal muscle atrophy, a loss in peak force and power, and an increased susceptibility to fatigue. The posterior compartment muscles of the lower leg (calf muscle group) appear to be particularly susceptible. Following only 1 wk in space or HU, rat soleus muscle showed a 30 to 40% loss in wet weight. After 3 wk of HU, almost all of the atrophied soleus fibers showed a significant increase in maximal shortening velocity (V(sub 0)), while only 25 to 30 % actually transitioned to fast fibers. The increased V(sub 0), was protective in that it reduced the decline in peak power associated with the reduced peak force. When the soleus is stimulated in situ following HU or zero-g one observes an increased rate and extent of fatigue, and in the former the increased fatigue is associated with a more rapid depletion of muscle glycogen and lactate production. Our working hypothesis is that following HU or spaceflight in rats and bed rest or spaceflight in humans limb skeletal muscles during contractile activity depend more on carbohydrates and less on fatty acids for their substrate supply. Baldwin et al. found 9 days of spaceflight to reduce by 37% the ability of both the high and low oxidative regions of the vastus muscle to oxidize long-chain fatty acids. This decline was not associated with any change in the enzymes of the tricarboxylic acid cycle or oxidation pathway. The purpose of the current research was to establish the extent of functional change in the slow type I and fast type H fibers of the human calf muscle following 17 days of spaceflight, and determine the cellular mechanisms of the observed changes. A second goal was to study the effectiveness of high resistance isotonic and isometric exercise in preventing the deleterious functional changes associated with unloading.

Fitts, R. H.↗
NASA NTRS1999

Protein kinetics during and after long-duration spaceflight on MIR

Human spaceflight is associated with a loss of body protein. Bed rest studies suggest that the reduction in the whole body protein synthesis (PS) rate should be approximately 15%. The objectives of this experiment were to test two hypotheses on astronauts and cosmonauts during long-duration (>3 mo) flights on MIR: that 1) the whole body PS rate will be reduced and 2) dietary intake and the PS rate should be increased postflight because protein accretion is occurring. The 15N glycine method was used for measuring whole body PS rate before, during, and after long-duration spaceflight on the Russian space station MIR. Dietary intake was measured together with the protein kinetics. Results show that subjects lost weight during flight (4.64 +/- 1.0 kg, P < 0.05). Energy intake was decreased inflight (2,854 +/- 268 vs. 2,145 +/- 190 kcal/day, n = 6, P < 0.05), as was the PS rate (226 +/- 24 vs. 97 +/- 11 g protein/day, n = 6, P < 0.01). The reduction in PS correlated with the reduction in energy intake (r2 = 0.86, P < 0.01, n = 6). Postflight energy intake and PS returned to, but were not increased over, the preflight levels. We conclude that the reduction in PS found was greater than predicted from ground-based bed rest experiments because of the shortfall in dietary intake. The expected postflight anabolic state with increases in dietary intake and PS did not occur during the first 2 wk after landing.

STS-40 Shuttle Project↗
NASA NTRS2007

Monitoring Immune System Function and Reactivation of Latent Viruses in the Artificial Gravity Pilot Study

Numerous studies have indicated that dysregulation of the immune system occurs during or after spaceflight. Using 21 day -6 deg. head-down tilt bed rest as a spaceflight analog, this study describes the effects of artificial gravity as a daily countermeasure on immunity, stress and reactivation of clinically important latent herpes viruses. The specific aims were to evaluate psychological and physiological stress, to determine the status of the immune system and to quantify reactivation of latent herpes viruses. Blood, saliva, and urine samples were collected from each participating subject at different times throughout the study. An immune assessment was performed on all treatment and control subjects that consisted of a comprehensive peripheral immunophenotype analysis, intracellular cytokine profiles and a measurement of T cell function. The treatment group displayed no differences throughout the course of the study with regards to peripheral leukocyte distribution, cytokine production or T cell function. Shedding of EBV and CMV was quantified by real time PCR in saliva and urine samples, respectively. There was no significant difference in CMV DNA in the treatment group as compared to the control group. EBV and VZV on the other hand showed a mild reactivation during the study. There were no significant differences in plasma cortisol between the control and treatment groups. In addition, no significant differences between antiviral antibody titers (EBV-VCA, -EA, -EBNA, CMV) or tetramer-positive (EBV, CMV) were found between the two groups. EBV DNA copies in blood were typically undetectable but never exceeded 1,500 copies per 10(exp 6) PBMCs. These data indicate that the artificial gravity countermeasure and the 21 day head-down tilt bed rest regimen had no observable adverse effect on immune function.

Mehta, Satish↗
NASA NTRS2007

Monitoring Immune System Function and Reactivation of Latent Viruses in the Artificial Gravity Pilot Study

Numerous studies have indicated that dysregulation of the immune system occurs during or after spaceflight. Using 21 day -6 degrees head-down tilt bed rest as a spaceflight analog, this study describes the effects of artificial gravity (AG) as a daily countermeasure on immunity, stress and reactivation of clinically important latent herpes viruses. The specific aims were to evaluate psychological and physiological stress, to determine the status of the immune system, and to quantify reactivation of latent herpes viruses. Blood, saliva, and urine samples were collected from each participating subject at different times throughout the study. An immune assessment was performed on all treatment and control subjects that consisted of a comprehensive peripheral immunophenotype analysis, intracellular cytokine profiles and a measurement of T cell function. The treatment group displayed no differences throughout the course of the study with regards to peripheral leukocyte distribution, cytokine production or T cell function. Shedding of Epstein barr virus (EBV), Cytomegalovirus (CMV), and Varicella zoster virus (VZV) was quantified by real time PCR in saliva and urine samples, respectively. There was no significant difference in CMV DNA in the treatment group as compared to the control group. EBV and VZV on the other hand showed a mild reactivation during the study. There were no significant differences in cortisol between the control and treatment groups. In addition, no significant differences between antiviral antibody titers (EBV-VCA, -EA, -EBNA, CMV) or tetramer-positive (EBV, CMV) were found between the two groups. EBV DNA copies in blood were typically undetectable but never exceeded 1,500 copies per 106 PBMCs. Overall, these data indicate that the artificial gravity countermeasure and the 21 day head-down tilt bed rest regimen had no observable adverse effect on immune function.

Mehta, Satish K.↗
NASA NTRS2000

Deconditioning and Reconditioning: Humans in Stressful Environments

Deconditioning is an integrated physiological response of the body to a reduction in metabolic rate; that is, to a reduction in energy use or in exercise level. While it may involve assumption of a horizontal body position, it certainly perturbs bodily homeostasis - at least temporarily. The reduction in physical activity that causes deconditioning is often associated with an increase in the time spent, for whatever reason, in a sitting or horizontal position. As a result, orthostatic factors may also contribute to the deconditioning mechanism. The word decondition may be defined as "1: to cause extinction of (a conditioned response) 2: to cause to lose physical fitness". This definition implies that psychological/emotional factors may accompany physical deconditioning, and it is this interpretation of the word that is used throughout this volume. It is apparent that deconditioning plays a major role in the mechanism of the general adaptive (homeostatic) response that is initiated by exposure to prolonged bed rest (BR). And the total homeostatic response to BR involves more than deconditioning per se. For example, it has been shown that the restoration of plasma volume and maximal work capacity after 4 weeks of BR deconditioning left other bodily functions (submaximal exercise oxygen uptake and cardiac output, leg proprioception and posterior leg muscle thickness and volume, head-up tilt tolerance, and sleep quality) functioning at decreased levels. The precise effect of deconditioning on BR homeostasis is difficult to determine, because the fundamental interactive neuro-endocrine-immune control networks that facilitate conditioning and deconditioning also act to maintain basic wholebody homeostasis. For example, is the mechanism of BR-induced deconditioning independent of the mechanism that provokes concomitant orthostatic intolerance; that is, fainting? Assumption of the recumbent body position for prolonged periods of time, results in a new adaptive-homeostatic state. This state occurs in response to the mutually interactive effects of the change in bodily position (hydrostatic pressure), to the virtual elimination of longitudinal pressure on the bones, to the increased confinement with possible reduction in total daily energy (exercise) expenditure, to the reorientation of stimuli within the vestibular organs, and (often) to altered socio-psychological conditions. The exercise-training (reconditioning) syndrome affects total body homeostasis by facilitating increases in work capacity and endurance, whereas deconditioning decreases physical performance. There are many interrelated factors that influence the control parameters that seek to maintain the adaptive conditioning-deconditioning syndrome. These control parameters can be better elucidated by subjecting otherwise healthy ambulatory people to various stresses, such as exercise training and prolonged spaceflight, bed rest, water immersion, hyperbaria, and isolation and confinement. Changes in control parameters will be manifested in muscle function, orthostatic tolerance, cardiorespiratory responses, musculo-skeletal systems, free-radical processes, and body thermoregulation with overarching effects on the subjects' psycho-sociological states. A discussion of these factors and the control parameters constitutes the substance of this volume. Special emphasis is placed on delineating practical applications of the findings that will be of special interest to physicians, nurses, and other health-care workers.

Greenleaf, John E.↗
NASA NTRS2010

Squat Ground Reaction Force on a Horizontal Squat Device, Free Weights, and Smith Machine

Bed rest is an analog to spaceflight and advancement of exercise countermeasures is dependent on the development of exercise equipment that closely mimic actual upright exercise. The Horizontal Squat Device (HSD) was developed to allow a supine exerciser to perform squats that mimic upright squat exercise. PURPOSE: To compare vertical ground reaction force (GRFv) on the HSD with Free Weight (FW) or Smith Machine (SM) during squat exercise. METHODS: Subjects (3F, 3M) performed sets of squat exercise with increasing loads up to 1-repetition (rep) maximum. GRF data were collected and compared with previous GRF data for squat exercise performed with FW & SM. Loads on the HSD were adjusted to magnitudes comparable with FW & SM by subtracting the subject s body weight (BW). Peak GRFv for 45-, 55-, 64-, & 73-kg loads above BW were calculated. Percent (%) difference between HSD and the two upright conditions were computed. Effect size was calculated for the 45-kg load. RESULTS: Most subjects were unable to lift >45 kg on the HSD; however, 1 subject completed all loads. Anecdotal evidence suggested that most subjects shoulders or back failed before their legs. The mean % difference are shown. In the 45-kg condition, effect sizes were 0.37 & 0.83 (p>0.05) for HSD vs. FW and HSD vs. SM, respectively, indicating no differences between exercise modes. CONCLUSION: When BW was added to the target load, results indicated that vertical forces were similar to those in FW and SM exercise. The exercise prescription for the HSD should include a total external resistance equivalent to goal load plus subject BW. The HSD may be used as an analog to upright exercise in bed rest studies, but because most subjects were unable to lift >45 kg, it may be necessary to prescribe higher reps and lower loads to better target the leg musculature

Scott-Pandorf, Melissa M.↗
NASA NTRS2007

Interactions between Artificial Gravity, Affected Physiological Systems, and Nutrition

Malnutrition, either by insufficient supply of some nutrients or by overfeeding has a profound effect on the health of an organism. Therefore, optimal nutrition is mandatory on Earth (1 g), in microgravity and also when applying artificial gravity to the human system. Immobilization like in microgravity or bed rest also has a profound effect on different physiological systems, like body fluid regulation, the cardiovascular, the musculoskeletal, the immunological system and others. Up to now there is no countermeasure available which is effective to counteract cardiovascular deconditioning (rf. Chapter 5) together with maintenance of the musculoskeletal system in a rather short period of time. Gravity seems therefore to be one of the main stimuli to keep these systems and application of certain duration of artificial gravity per day by centrifugation has often been proposed as a very potential countermeasure against the weakening of the physiological systems. Up to now, neither optimal intensity nor optimal length of application of artificial gravity has been studied sufficiently to recommend a certain, effective and efficient protocol. However, as shown in chapter 5 on cardiovascular system, in chapter 6 on the neuromuscular system and chapter 7 (bone and connective system) artificial gravity has a very high potential to counteract any degradation caused by immobilization. But, nutrient supply -which ideally should match the actual needs- will interact with these changes and therefore has also to be taken into account. It is well known that astronauts beside the Skylab missions- were and are still not optimally nourished during their stay in space (Bourland et al. 2000;Heer et al. 1995;Heer et al. 2000b;Smith et al. 1997;Smith & Lane 1999;Smith et al. 2001;Smith et al. 2005). It has also been described anecdotally that astronauts have lower appetites. One possible explanation could be altered taste and smell sensations during space flight, although in some early space flights no significant changes were found (Heidelbaugh et al. 1968;Watt et al. 1985). However, data from a recent head-down bed rest study showed significant decrease in smell sensation (Enck et al. unpublished data) suggesting that fluid shifts might have an impact. If this holds true and which has to be validated in further studies, this seems to play an important role for lowered food intake causing insufficient energy intake and subsequently insufficient supply of most of the macro- and micronutrients. Other nutrients are taken in excess, for example sodium. As it is very well known from daily food consumption especially premanufactured food with high salt content seems to be more palatable than that with low salt content. Salt also functions as preservation which is very important taking into account the space food system limitations (i.e., lack of refrigerators and freezers). The preference for food with high salt intake by astronauts might therefore very likely be caused by altered smell and taste sensations in microgravity.

Heer, Martina↗