Search

We studied the influence of ionizing radiation and hypogravity as negative factors of space flights on DNA damage in peripheral blood lymphocytes of rhesus monkeys at different times after exposure (from 1 to 446 days). The proportion of cells with high numbers of DNA double-strand breaks (DSB), positive for the surrogate DSB marker-protein γH2AX, was monitored using flow cytometry. Some animals were exposed to 7-day antiorthostatic hypokinesia simulating hypogravity, the others to a combined effect of antiorthostatic hypokinesia, whole-body γ-irradiation (2.34 cGy/h, dose 1 Gy), and irradiation of the head with 12 C ions (450 MeV, dose 1 Gy). Exposure to antiorthostatic hypokinesia led to a significant increase in the proportion of γH2AX + lymphocytes only on the first day after exposure, whereas after combined exposure, increased numbers of damaged lymphocytes were recorded up to 42 days after exposure., (© 2021. Springer Science+Business Media, LLC, part of Springer Nature.)

The control of bipedal stance and the capacity to regain postural equilibrium after its deterioration in variable gravities are crucial prerequisites for manned space missions. With an emphasize on natural orthograde posture, computational techniques synthesize muscle activation patterns of high complexity to a simple synergy organization. We used nonnegative matrix factorization to identify muscle synergies during postural recovery responses in human and to examine the functional significance of such synergies for hyper-gravity (1.75 g) and hypo-gravity (0.25 g). Electromyographic data were recorded from leg, trunk and arm muscles of five human exposed to five modes of anterior and posterior support surface translations during parabolic flights including transitional g-levels of 0.25, 1 and 1.75 g. Results showed that in 1 g four synergies accounted for 99% of the automatic postural response across all muscles and perturbation directions. Each synergy in 1 g was correlated to the corresponding one in 0.25 and 1.75 g. This study therefore emphasizes the similarity of the synergy organization of postural recovery responses in Earth, hypo- and hyper-gravity conditions, indicating that the muscle synergies and segmental strategies acquired under terrestrial habits are robust and persistent across variable and acute changes in gravity levels.

The use of shock wave therapy (SWT) and low-intensity pulsed ultrasound (LIPUS) as countermeasures to the inhibited fracture healing experienced during mechanical unloading was investigated by administering treatment to the fracture sites of mature, female, Rambouillet Columbian ewes exposed to partial mechanical unloading or full gravitational loading. The amount of fracture healing experienced by the treatment groups was compared to controls in which identical surgical and testing protocols were administered except for SWT or LIPUS treatment. All groups were euthanized after a 28-day healing period. In vivo mechanical measurements demonstrated no significant alteration in fixation plate strains between treatments within either partial unloading group. Similarly, DXA BMD and 4-point bending stiffness were not significantly altered following either treatment. μCT analyses demonstrated lower callus bone volume for treated animals (SWT and LIPUS, p < 0.01) in the full gravity group but not between reduced loading groups. Callus osteoblast numbers as well as mineralized surface and bone formation rate were significantly elevated to the level of the full gravity groups in the reduced loading groups following both SWT and LIPUS. Although no increase in 4-week mechanical strength was observed, it is possible that an increase in the overall rate of fracture healing (i.e., callus strength) may be experienced at longer time points under partial loading conditions given the increase in osteoblast numbers and bone formation parameters following SWT and LIPUS. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:921-929, 2018., (© 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.)

We evaluated different lymphocyte populations and levels of plasma cytokines in peripheral blood as well as inflammatory infiltration and expressions of cytokines in lung tissues derived from macaque under long-term stimulated microgravity through being suspended in an antiorthostatic position so as to identify relevant immune parameters and to understand potential mechanisms of lung injury. Fifteen healthy male rhesus macaques were randomly divided into groups 1 (control, n = 5), groups 2 (head-down tilting for 6 weeks, n = 5), and groups 3 (head-down tilting for 6 weeks and recovery for 4 weeks, n = 5). Lymphocyte subsets in peripheral blood were analyzed using flow cytometry and the concentrations of 14 cytokines in plasma were measured with Luminex multiplexing technology. HE staining and transmission electron microscopy were employed to investigate the morphologies and subcellular structures of lung tissues. Immunohistochemistry and real-time PCR were employed to explore mRNA and protein expressions of cytokines in lung tissues. Immunohistochemical demonstrations were detected for CD3, CD4, CD8 T lymphocytes, CD20 B lymphocytes, and CD68 macrophages in lung tissues. Compared to group 1, groups 2 and 3 showed a decrease in the percentage of CD2+T cells, CD2+CD4+T helper cells, and CD2+CD8+cytotoxic T cells as well as an increase in the expression of CD95 on the surface of T lymphocytes in peripheral blood. The serum cytokine levels of IL-18 and TNF-α were increased in group 2 when compared to groups 1 and 3. HE and TEM observed changes in the structure and ultrastructure of lung tissues in groups 2 and 3. The number of CD3+T cell, CD4+T cell, CD8+T cells, and CD68+macrophage and the expression levels of IL-1β, IL-6, and IL-18 in lung tissues were increased in groups 2 when compared with groups 1 and 3. Our data suggested that long-term microgravity might alter the functions of immune system and cause lung damage, changing lymphocyte distribution and functions as well as cytokine production.

Objectives: We investigated the dose-effect relationship between wide changes in gravity from 0 to 2.0 Gz (Δ0.5 Gz) and cerebral blood flow (CBF), to test our hypothesis that CBF has a linear relationship with levels of gravity., Subjects and Methods: Ten healthy seated men were exposed to 0, 0.5, 1.0, 1.5, and 2.0 Gz for 21 min, by using a tilt chair and a short-arm human centrifuge. Steady-state CBF velocity (CBFV) in the middle cerebral artery by transcranial Doppler ultrasonography, mean arterial pressure (MAP) at the heart level (MAPHeart), heart rate, stroke volume, cardiac output and respiratory conditions were obtained for the last 6 min at each gravity level. Then, MAP in the middle cerebral artery (MAPMCA), reflecting cerebral perfusion pressure, was estimated., Results: Steady-state CBFV decreased stepwise from 0.5 to 2.0 Gz. Steady-state heart rate, stroke volume, estimated MAPMCA and end-tidal carbon dioxide pressure (ETCO2) also changed stepwise from hypogravity to hypergravity. On the other hand, steady-state MAPHeart and cardiac output did not change significantly. Steady-state CBFV positively and linearly correlated with estimated MAPMCA and ETCO2 in most subjects., Conclusion: The present study demonstrated stepwise gravity-induced changes in steady-state CBFV from 0.5 to 2.0 Gz despite unchanged steady-state MAPHeart. The combined effects of reduced MAPMCA and ETCO2 likely led to stepwise decreases in CBFV. We caution that a mild increase in gravity from 0 to 2.0 Gz reduces CBF, even if arterial blood pressure at the heart level is maintained.

The literature is deficient with regard to how the localized mechanical environment of skeletal tissue is altered during reduced gravitational loading and how these alterations affect fracture healing. Thus, a finite element model of the ovine hindlimb was created to characterize the local mechanical environment responsible for the inhibited fracture healing observed under experimental simulated hypogravity conditions. Following convergence and verification studies, hydrostatic pressure and strain within a diaphyseal fracture of the metatarsus were evaluated for models under both 1 and 0.25 g loading environments and compared to results of a related in vivo study. Results of the study suggest that reductions in hydrostatic pressure and strain of the healing fracture for animals exposed to reduced gravitational loading conditions contributed to an inhibited healing process, with animals exposed to the simulated hypogravity environment subsequently initiating an intramembranous bone formation process rather than the typical endochondral ossification healing process experienced by animals healing in a 1 g gravitational environment. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1206-1215, 2016., (© 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.)

Unlabelled: Swimming during adolescence has shown neutral or even negative effects on bone mass. Nevertheless, it is still unknown if these effects are due to swimming or to other factors, such as sedentary behaviors., Introduction: Three objectives were described (1) to measure objective physical activity (PA) additional to swimming performed by adolescent swimmers (SWI) and compare it to that performed by normo-active controls (CG), (2) to describe the relationship between objectively measured PA and bone mass, and (3) to compare bone mass of swimmers that meet the World Health Organization PA guidelines (active) WHO and those that do not (inactive)., Methods: A total of 71 SWI (33 females) and 41 CG (17 females) wore an accelerometer for at least 4 days. PA was expressed as the amount of time (minutes/day) in each intensity [sedentary/light/moderate or vigorous (VPA), and the sum of moderate and vigorous (MVPA)]. Using the cutoff points proposed by Vanhelst et al. SWI were classified as active or inactive according to whether they reached 60 min of weight-bearing MVPA per day or not. Bone mineral density (BMD) was measured by dual energy X-ray absorptiometry, and bone strength values were calculated with peripheral quantitative computed tomography. Differences in PA intensities were calculated between SWI and CG. The relation of VPA to bone mass was studied in the SWI., Results: Male-SWI spend less time in VPA and MVPA than male-GC, which partly explains the lower BMD values in SWI than CG., Conclusion: Swimming may displace weight-bearing VPA with serious implications on bone health.

Intraocular pressure (IOP) and eye hydrodynamics (aqueous outflow easiness rate (C) and moisture chamber production (F)) were studied in 9 adult volunteers subjected to the hypogravity effects of head-down tilt (HDT) at -15⁰ to the horizontal plane. The volunteers stayed in the horizontal and tilted positions for 10 minutes. IOP was measured according to Maklakov (tonometer 5 g), C and F - according to Nesterov (simplified tonography). In parallel, heart rate (HR) and systolic and diastolic blood pressures (SBP and DBP) were measured in the sitting, lying and tilted positions. In HDT IOP rose 10.3 % (p < 0.05) and C reduced 60 % (p < 0.05); F showed an uncertain trend down by 59 % (p > 0.05). Increase of the Bekker coefficient by 168 % (p < 0.05) could testify interconnection of the increased IOP and impaired moisture outflow. Moreover, in HDT DBP showed a rise while HR decreased. These results suggest that during brief tilt- down IOP increases not only because of a greater filling of the choroid vessels, but also because of retarded outflow of the intraocular fluid. The downward trend in fluid production can be a compensatory reaction to increased'IOP.

Lumbar puncture (LP) is a commonly performed low-risk procedure terrestrially, used diagnostically for evaluation of cerebrospinal fluid (CSF) pressure as well as for collection of CSF for analysis. NASA is investigating noninvasive means for measurement of intracranial pressure (ICP) to assess the potential contribution of elevated intracranial pressures to recently reported changes in astronauts' visual acuity and eye anatomy, known collectively as the Visual Impairment/Intracranial Pressure risk. However, many of these noninvasive technologies are still under development, have limited clinical validation, are several years away from being ready for in-flight use, or only provide qualitative rather than quantitative ICP values. Therefore, performance of in-flight LPs, as part of crewmember evaluation, has also been considered by NASA. This manuscript summarizes the unique operational considerations, constraints, concerns, and limitations of using traditional LP as an adjunct or as an alternative to noninvasive ICP measurements during spaceflight.

Introduction: Red Bull Stratos was a commercial program that brought a test parachutist protected by a full pressure suit to 127,852 ft (38,964 m), via a stratospheric balloon with a pressurized capsule, from which he free fell and subsequently parachuted to the ground. In light of the uniqueness of the operation and the medical threats faced, medical protocols specific to distinctive injury patterns were developed. One unique threat was that of a flat spin during free fall with resultant exposure to -Gz (toe-to-head) acceleration. In preparation for stratospheric free fall, the medical team conducted a review of the literature on the spectrum of human and animal injury patterns attributable to -Gz exposures. Based on the findings, an emergency medical field response protocol was developed for the rapid assessment, diagnosis, and treatment of individuals suspected of -Gz injury., Methods: A systematic review was conducted on available literature on human and animal studies involving significant -Gz exposure, with subsequent development of an applicable field treatment protocol., Results: The literature review identified pathophysiologic processes and mitigation strategies that were used to develop a prevention and treatment protocol, outlining appropriate interventions using current best medical practices. A medical field treatment protocol was successfully established for the high-altitude balloon program., Discussion: Available literature provided insight into best medical practices for the prevention and treatment of significant -Gz exposures during high-altitude parachute activity. Using the protocol developed for the field medical response, injuries from sustained -Gz exposure can be effectively managed in similar high-altitude and space operations.

When modeling effects of hypogravitation by the method of hindlimb unloading in rats the area of cross-section in lumbar part of a spinal cord was found to reduce. The analysis of spinal cord slides showed that these changes are associated with a decrease in the area of white substance of a spinal cord. Data obtained are consistent with our previous observation of a decrease in expression of the genes encoding myelin proteins. Results of our researches give the good reasons to believe that miyelinization failure in CNS is one of the factors that underlie the development of hypogravitational motor syndrome.

The aim of the present study was to investigate the effects of abnormal gravity on human mesenchymal stem cells (hMSCs). Strong magnetic field and magnetic field gradient generate a magnetic force that can add to or subtract from the gravitational force. In this study, this is defined as a high-magneto-gravitational environment (HMGE). The HMGE provides three apparent gravity levels, i.e. hypogravity (μg), hypergravity (2g) and normal gravity with strong magnetic field (1g) conditions. After hMSCs were subject to HMGE for 12 h, the proliferation, morphology, structure and apoptosis were investigated. Results showed that the proliferation of hMSCs was inhibited under μg condition. The abnormal gravity induced morphologic characteristics of apoptosis cells, such as cell shrinkage, membrane blebbing, nuclear chromatin condensation and margination, decreased cell viability, and increased caspase-3/7 activity. The rate of apoptosis under μg condition is up to 56.95%. The F-actin stress fibers and microtubules were disrupted under abnormal gravity condition. Under μg-condition, the expression of p53 at mRNA and protein levels was up-regulated more than 9- and 6 folds, respectively. The Pifithrin-α, an specific inhibitor of p53, inhibited the apoptosis and prevented the disruption of cytoskeleton induced by abnormal gravity. These results implied that hMSCs were sensitive to abnormal gravity and exhibited classic apoptotic features, which might be associated with p53 signaling.

Microgravity affects the different organ systems to various degrees. In particular, a thoracocephalic fluid shift occurs through suppression of the hydrostatic gradient. Sensory conflict leads to space motion sickness, which is frequent early in the flight, and the musculo-skeletal system is perturbed by the lack of stimuli. The respiratory system seems to be less affected. These changes do not seem to impair health or performance. Humans seem able to adapt to long-term exposure to microgravity, but disorders can occur on return to Earth. In-flight preventive measures need be developed.

Downsizing of muscle fibers, decline of their contractility and alteration of the myosin phenotype towards fast isoforms prevalence are ranked among the main consequences of gravitational unloading of postural muscles. Role of Ca2+ ions in these processes is the subject of the article. Authors revealed increase in the Ca2+ content in myofibers of resting m. soleus of mice following hindlimb suspension. It has been also reported earlier that nifedipine, a specific blocker of calcium L-channels, can prevent this increase acting on the central and local controls. Therefore, a supposition can be made that activation of the dehydropyridine Ca channels is responsible for Ca2+ rest accumulation during gravitational unloading. The calcium-dependent signaling pathways may be thought of as key players in a number of developments due to gravitational unloading. To begin with, already in early 1990s this role in the hypogravity-induced muscle atrophy was ascribed to calpains, Ca-dependent proteinases which was clearly demonstrated later. We observed maintenance of the relative titin and nebulin contents in unloaded m. soleus associated with the effect of Ca chelators. Also, nifedipine injection reduced significantly the growth of MHC fast isoforms expression during gravitational unloading equally on the RNA and protein levels. To bring to light the place of calcineurin/NFAT signaling system in the MHC phenotype alteration, we undertook inhibition of this pathway by injection of cyclosporine A. This resulted in getting evidence of the stabilizing function of this pathway as it opposes to the myosin phenotype transformation to the fast one.

Creating conditions similar to those occurring during exposure of cells to microgravity modulates endothelial functions. We have previously demonstrated that human macrovascular endothelial cells in simulated hypogravity proliferate faster than controls, partly because they downregulate interleukin 1alpha. On the contrary, murine microvascular endothelial cells are growth inhibited in simulated hypogravity, and this is due, at least in part, to the decrease of interleukin 6. Since endothelial cells are very heterogeneous and differences between various species have been reported, we exposed human microvascular cells to gravitational unloading and found that it retards cell growth without affecting cell migration. Interestingly, we detected the induction of Tissue Inhibitor of Metalloprotease-2, which inhibits endothelial growth in vitro and angiogenesis in vivo. Together with the finding that hypogravity stimulates the synthesis of nitric oxide, involved also in neovascularization, our results underscore a modulation of the angiogenic properties of microvascular human endothelial cells. We also show that hypogravity inhibits proteasome activity, thus suggesting that post-translational mechanisms are involved in the adaptations of these cells to hypogravity. These results underscore that hypogravity differently impacts on micro- and macro-vascular human endothelial cells. In particular, these results may shed some light on the molecular mechanisms contributing to the impairment of angiogenesis observed in different models in space. Our data might also explain why bioengineered tissues to be used for regenerative medicine fail to neovascularize when assembled in simulated hypogravity.

Purpose: In space, astronauts are subject to microgravity, which reduces skeletal loading and osteoblast function and can cause bone resorption and a decrease in bone density. No known research to date has studied the effect of microgravity on dental implants. This study evaluated peri-implant bone changes around a dental implant placed in a French astronaut who spent 6 months in Russia's Mir Space Station., Materials and Methods: Measurements were performed by 2 examiners before the flight (baseline), after the flight (stage 1), and following a recovery period (stage 2). Standardized periapical radiographs were taken, and data were recorded using a photomicroscope and a measuring scale., Results: Cumulatively, the implant sustained 0.43 mm of mesial bone gain and 0.31 mm of distal bone loss., Discussion: The observed peri-implant bone height changes were within normal limits and the implant appeared very stable during the course of this study., Conclusion: Peri-implant bone levels remained stable after 6 months in microgravity, and the implant continued to function without complications.

Introduction: We investigated the effects of head-down tilt (HDT), which simulates microgravity during spaceflights, on the choroidal pulsatile ocular blood flow (POBF). This investigation is important because alterations in the choroidal blood flow can affect the function of retinal rods and cones that rely totally on the choroid for metabolites., Methods: Nineteen healthy adults between 20 and 38 yr of age participated in this study. The POBF was compared for: 1) baseline, wherein subjects were declined 30 degrees from vertical; 2) microgravity simulation where subjects were in a 7 degrees HDT for 2 min; 3) 90 min of the 7 degrees HDT; and 4) recovery, i.e., back at 30 degrees for 2 min., Results: The group averaged POBF (Mean +/- SEM values: 828.43 +/- 48.88 microL x min(-1)) decreased immediately during the 2-min microgravity simulation (582.18 +/- 43.62 microL x min(-1)), remained at that inferior level at the 90-min mark of HDT (542.26 +/- 45.35 microL x min(-1)), and came back toward baseline POBF during the recovery period (760.11 +/- 46.03 microL x min(-1)) (p = 0.0001)., Discussion: The results show that simulated-microgravity of relatively short duration induces retinal hypoperfusion throughout the microgravity interval through the reduction in the POBF. This finding may have important implications regarding visual performance in space crewmembers placed in prolonged microgravity environments.

Background: Long-duration space missions, as well as emerging civilian tourist space travel activities, prompted review and assessment of data available to date focusing on cardiovascular risk and available risk mitigation strategies. The goal was the creation of tools for risk priority assessments taking into account the probability of the occurrence of an adverse cardiovascular event and available and published literature from spaceflight data as well as available risk mitigation strategies., Methods: An international group of scientists convened in Bellagio, Italy, in 2004 under the auspices of the Aerospace Medical Association to review available literature for cardiac risks identified in the Bioastronautics Critical Path Roadmap (versions 2000, 2004). This effort led to the creation of a priority assessment framework to allow for an objective assessment of the hazard, probability of its occurrence, mission impact, and available risk mitigation measures., Results/conclusions: Spaceflight data are presented regarding evidence/ no evidence of cardiac dysrhythmias, cardiovascular disease, and cardiac function as well as orthostatic intolerance, exercise capacity, and peripheral resistance in presyncopal astronauts compared to non-presyncopal astronauts. Assessment of the priority of different countermeasures was achieved with a tabular framework with focus on probability of occurrence, mission impact, compliance, practicality, and effectiveness of countermeasures. Special operational settings and circumstances related to sensitive portions of any mission and the impact of environmental influences on mission effectiveness are addressed. The need for development of diagnostic tools, techniques, and countermeasure devices, food preparation, preservation technologies and medication, as well as an infrastructure to support these operations are stressed. Selected countermeasure options, including artificial gravity and pharmacological countermeasures need to be systematically evaluated and validated in flight, especially after long-duration exposures. Data need to be collected regarding the emerging field of suborbital and orbital civilian space travel, to allow for sound risk assessment.

Introduction: This study was designed to elucidate the effect of short-arm centrifuge-induced artificial gravity with exercise training during ground-based simulated spaceflight, i.e., prolonged head-down bed rest (HDBR), on respiratory and cardiovascular responses to upright exercise., Methods: There were 10 healthy men who underwent 20 d of -6 degrees HDBR, and were assigned to either a countermeasure (CM) group (n = 5) or a no countermeasure (No-CM) group (n = 5). The subjects in the CM group performed two sessions (20 min each session, 40 min total) of short-arm centrifuge-induced artificial gravity with exercise training in a supine position on alternate days (10 d total) during HDBR. The first session was set at 0.8-1.4 G load at heart level with a constant exercise intensity (60 W), and the second session began with a 0.3 G load at heart level with an interval exercise protocol (40-80% peak oxygen uptake; VO2peak). The measurements of respiratory and cardiovascular responses to incremental exercise were performed pre- and post-HDBR., Results: The 20 d of HDBR increased minute expired ventilation, heart rate, and respiratory exchange ratio and decreased stroke volume during submaximal exercise in the No-CM group, whereas these parameters were unchanged in the CM group. In the No-CM group, VO2peak decreased significantly (47.0 +/- 8.6 to 34.8 +/- 6.8 ml x kg(-1) x min(-1), p < 0.05), whereas VO2peak in the CM group did not show a significant decrease following 20 d of HDBR (47.7 +/- 10.0 to 43.9 +/- 8.9 ml x kg(-1) x min(-1)). These results suggest that short-arm centrifuge-induced artificial gravity with exercise training is effective in maintaining respiratory and cardiovascular responses to upright exercise.

Architectonics of the fibrillar actin in cultures of human endothelium cells (EC) during and after extended (144 hrs.) clinostatting was examined under the fluorescent microscope. In control EC cultures, F-actin was composed of a network of filaments located both in the center and along the periphery of cells. One hour of rotation did not visibly affect the actin skeleton, however, in two hours there were cells with filaments displaced toward the membrane. Twenty-four hours of rotation caused total remodeling of the cytoskeleton so that practically the whole population of thin filaments had migrated toward the periphery. In most of the cells the intercell contact area formed undulating edges rich in F-actin. A similar picture could be seen after 144 hrs. of rotation. The actin skeleton partially recovered in 4 hrs. and regained the normal structure in 24 hrs. of rehabilitation. Same period was required for cells to restore their structure completely following the extended clinostatting. These data suggest sensitivity of the EC cytoskeleton to changes in the gravity vector. Remodeling of the actin skeleton in a changed gravity is reversible and proceeds more rapidly than recovery.

Background: Modern, thrust-vectored jet aircraft have the capability of developing multi-axis accelerations, especially during the performance of "supermaneuvers." These "agile" aircraft are capable of unconventional flight. The human consequences of this agile flight environment are unknown., Methods: This multi-axis acceleration environment was studied on the Dynamic Environment Simulator gimbaled centrifuge. There were nine relaxed, unprotected subjects who were exposed to either lateral (+/- 1, +/- 2 Gy), transverse chest-to-back (+1, 2.5, or 4 Gx), or back-to-chest (-1 Gx) sustained acceleration. Positive C (+Gz) acceleration was then added beginning at 1.0 Gz by gradual onset (0.1 Gz x s(-1)) until the subjects lost nearly all of their vision. Baseline +Gz-only relaxed tolerances were measured before and after all combined Gy/Gz and Gx/Gz exposures. Heart rate, percent cerebral oxygen saturation, and cerebral blood volumes were collected during each exposure., Results: Adding moderate transverse (+Gx) acceleration significantly reduced +Gz tolerance. Relaxed, unprotected +Gz tolerance was reduced approximately 0.25 G when 1.0 or 2.5 Gx was added to the increasing +Gz exposure. Adding moderate lateral Gy significantly increased +Gz tolerance. Relaxed, unprotected +Gz tolerance was increased approximately 0.5 G when +2 Gy or -2 Gy was added to the -Gz exposure. The decrease in cerebral blood volume was significantly less when +Gz was added to -1 Gx compared with the addition of +Gz to +Gx., Conclusions: Multi-axis sustained accelerations, such as those experienced during thrust-vectored aircraft maneuvers, can either enhance or reduce the +Gz tolerance of the pilot depending on the direction of the net gravitoinertial force. Gy acceleration in conjunction with Gz acceleration can enhance G tolerance. Gx acceleration in addition to Gz acceleration can reduce G tolerance.

Introduction: Previous research suggests that human sensorimotor performance depends both on task difficulty, and on the allocation of the brain's computational resources to the task. We employ this view to analyze the changes of sensorimotor performance during the microgravity episodes of parabolic flight., Methods: There were seven subjects who participated before, during, and after exposure to the microgravity episodes of parabolic flight. They performed a tracking task with one hand, and a four-choice reaction time task with the other hand, either alone or concurrently. Overall performance scores across tasks were calculated., Results: Overall single-task performance deteriorated by about 50% microgravity, with little sign of recovery during the flight. Overall dual-task interference was more than twice as great at the onset of microgravity than at the onset of the 1-G baseline, but converged toward that baseline within about 4.5 min., Conclusions: Our subjects accepted a consistently poor level of sensorimotor performance throughout exposure to microgravity. To maintain that level, they increased the allocation of computational resources to the tasks at the onset of microgravity, but an increase was no longer necessary after 4.5 min of microgravity exposure. We take the initial increase as evidence of a brief phase of sensorimotor adaptation.

Antiorthostaic hypokinesia (AOHK) was found to entail a considerable diminishing of the control system's precision abilities. In the first 14-30 days of the AOHK (the 1st stage), variability of interimpike intervals (ISI) was sharply increased as well as the degree of synchronisation of the motor units' (MU) activity; starting from the 30th day (the 2nd stage), a regular diminishing of the ISI occurred and the MU synchronisation disappeared. The data obtained suggest the different nature of the precision disorders during the 1st and the 2nd stages of the AOHK: a reflex responses to support unloading and the atrophic processes in the muscles, respectively.

Dynamic and fuzzy models for a typical subject's cardiovascular response to the orthostatic stress have been developed based on experimental data. In our original study (Cheung et al., 1999), arterial blood pressure (BP) time-series data were obtained using a man-rated tilt table that applies gigahertz-acceleration transitions from +0.861 Gz [head-up (HU)] to -0.707 G [head-down (HD)] and back to +0.861 Gz (HU) using either pitch or roll rotations (Cheung et al., 1999). G transitions of different duration and onset rates are common in fighter maneuvers. Based on these data, two types of predictive models have been developed in this paper: 1) second-order discrete-time models that predict BP dynamics during pitch and roll rotations and 2) fuzzy logic models that predict important variations in a subject's cardiovascular dynamics induced by HU-to-HD and HD-to-HU transitions. These two types of models assist in providing an operationally important predictive view on the characteristics of BP responses to orthostatic stress induced by pitch and roll rotations of a fighter jet pilot. The new models are being currently utilized in the design of operational recommendations for more G-tolerant operational flight regimes (e.g., split-S tactical maneuver) than the ones currently in use for modern combat aircraft.

Disuse of postural slow-twitch muscles, as it occurs in hypogravity, induces a slow-to-fast myofibre type transition. Nothing is known about the effects of weightlessness on the resting membrane chloride conductance (gCl), which controls sarcolemma excitability and influences fibre type transition during development and adult life. Using the current-clamp method, we observed that rat hindlimb unloading (HU) for 1-3 weeks increased gCl in fibres of the slow-twitch soleus (Sol) muscle toward values found in fast muscle. Northern blot analysis suggested that this effect resulted from an increased ClC-1 chloride channel mRNA level. In the meantime, a 4-fold increase in fibres expressing fast isoforms of the myosin heavy chain (MHC) was observed by immunostaining of muscle sections. Also, Sol muscle function evolved toward a fast phenotype during HU, as demonstrated by the positive shift of the threshold potential for contraction. After 3-days HU, Sol muscle immunostaining and RT-PCR experiments revealed no change in MHC protein and mRNA expression, whereas the gCl was already maximally increased, due to a pharmacologically probed, increased activity of ClC-1 channels. Thus the increase in gCl is an early event in Sol muscle experiencing unloading, suggesting that gCl may play a role in muscle adaptation to modified use. Pharmacological modulation of ClC-1 channels may help to prevent disuse-induced muscle impairment.

Background: No data are available about the short- or long-term influences of microgravity in space on the release of gastroenteropancreatic peptides, although these peptides are involved in the regulation of gastrointestinal functions., Methods: Fasting plasma samples were gained during the EUROMIR-94 mission from a European Space Agency (ESA) astronaut who experienced no signs of space motion sickness in orbit. Plasma concentrations of nine gastroenteropancreatic peptides were measured with sensitive and specific radioimmunoassays., Results: Fasting plasma levels of motilin, pancreatic polypeptide (PP), vasoactive intestinal peptide (VIP), and secretin were increased and plasma level of cholecystokinin (CCK) was decreased by acute exposure of the astronaut to microgravity. Chronic (4 wk) exposure caused an enhancement of plasma CCK, motilin, neurotensin, VIP, and insulin whereas plasma concentrations of PP, secretin, gastrin, and somatostatin showed no changes. During the 25-d stay on MIR station plasma levels of CCK, motilin, and neurotensin increased. Short-time body rotations caused an elevation of plasma levels of PP but decreased plasma motilin., Conclusions: As the influence of microgravity on the peptide levels was not uniform, an effect due to other factors (e.g., change in fluid balance or body weight) is unlikely. Moreover, adaptive changes of some peptides occurred during the stay in orbit. The release of PP and motilin seems to be very sensitive to rotation forces. These results have to be confirmed in more subjects in space to be able to link changes of gastroenteropancreatic peptide release to alterations of gastrointestinal functions.

G-transition effects are defined as the spectrum of physiological and psychophysical effects induced by rapid changes in gravitoinertial forces, alternating between hypogravity (<1 Gz) and hypergravity (>1 Gz) and vice versa. They appear to involve the cardiovascular and spatial orientation systems. This note attempts to briefly review past and current research efforts on the consequences of G-transitions and to examine potential confounding Coriolis-induced bias in both ground-based and inflight research. A brief review of current evidence of vestibular influence on orthostatic compensation and their implications for G tolerance is presented. The effects of roll-induced hypogravity on subsequent G tolerance and possible misperception of attitude during roll rotation are discussed. An integrated approach is recommended for future research on acceleration and disorientation.

Background: Exposure to reduced gravitational forces during spaceflight is associated with significant reductions in skeletal muscle mass and strength. The purpose of this study was to test the hypothesis that increases in resting cytosolic free calcium concentration ([Ca2+]i) would precede reductions in protein content and maximal isometric tetanic force (Po) in mouse soleus muscle after initiation of hindlimb suspension., Methods: Female ICR mice (n = 42) were hindlimb suspended for 1, 2, 3, 5, or 7 d; weight-matched mice were used as controls. Following the hindlimb suspension, the left soleus muscle was used to determine Po in vitro and the right soleus muscle was used to determine protein content and [Ca2+]i via confocal laser scanning microscopy., Results: Compared with controls, [Ca2+]i was elevated by 38% at 2 d, and 117% at 7 d. Compared with controls, soleus muscle total and myofibrillar protein contents were reduced 27-29% and 30-34%, respectively, at 5-7 d after initiation of hindlimb suspension. Compared with controls, soleus muscle Po was decreased by 24% at 3 d, and 38% at 7 d., Conclusion: It appears that resting cytosolic Ca2+ homeostasis is disturbed soon after the initiation of hindlimb suspension, and these elevations in [Ca2+]i may play a role in initiating soleus muscle atrophy.

Effects of long-term simulation of hypogravity on actin cytoskeleton and cell migration were investigated in cultured human endothelium cells (EC). In control, F-actin resided predominantly on the periphery of cell forming an array of parallel bundles with "dense bodies" along the edge. A small number of actin cable fibers was found in the center. Already after 1-2 hrs of clinostatting at 5 RPM the cell cytoskeleton showed actin filament thinning and displacement toward the cell edges. In subsequent 6-18 hrs, almost all actin fibers had left the center part of EC and had ranged themselves in a continuous F-actin line in the intercellular contact area. In most cases, these changes resulted in the so-called "ruff-edge". Since both the disappearance of cable fibers and formation of the "ruff-edge" add to the cell migration activity, this parameter was studied with the would-healing model. According to our data, 24-48 hrs of exposure to hypogravity stimulates cell migration and expedites 2-3 times reparation of mechanically damaged monolayer. The results suggest that effects of hypogravity on cultured human EC are likely to be consequent to alterations in the activity of protein kinase C and/or adenylate cyclase involving many members of the cellular metabolism.

To test the hypothesis that the body mass of rats is increased during spaceflight, we developed two models from the literature and obtained mass measurements during spaceflight. From studies of centrifugation (hypergravity), there is a reduction in body mass of rats dependent on the exposure gravity level. From data in 18 publications on rats subjected to hypergravity by centrifugation, we developed a model that predicted a 27% increase in body mass during the microgravity of spaceflight. Following spaceflight, with an increase in gravity on return to Earth, there is a reduction in body mass of rats for over 3 d. We related the reduction in body mass after spaceflight to the time after landing that mass measurements were made. From data in 23 publications on rats returning from spaceflight, we developed a model that predicted a 19% increase in body mass during spaceflight. Measurement of body mass of rats on days 6 and 10 of spaceflight found a 7 and 9% increase compared with ground control animals. The increase in body mass during spaceflight suggests that the rat may provide a viable model for metabolic studies in which changes during spaceflight may be predicted in part by ground-based hypergravity studies.

Background: The push-pull effect has been defined previously as decreased +Gz tolerance caused by previous baseline zero or -Gz exposure. Earlier work indicates that the delay in BP (BP) recovery during +Gz is a function of time at -G7, and is due to the lengthened time-course of sympathetically mediated peripheral vasoconstriction., Hypothesis: The purpose of this study was to retrospectively determine whether heart rate (HR) varies with BP as duration at preceding -Gz increased., Methods: Continuous ECG R-R interval data from 15 s of +2.25Gz after preceding 2, 5, 10, or 15 s at 2Gz obtained from previous experiments were analyzed and compared with the previously reported BP data. Repeated measures ANOVA and regression analyses were used to compare +2.25Gz HR responses after the four -Gz conditions and one control +2.25Gz condition., Results: An initial rapid rise in HR was observed for all conditions with a consistent steady-state plateau achieved after the first 7 s of +2.25Gz. However, there were significant differences in mean HR attained during the +2.25Gz plateau for preceding 15 s -2.0 Gz vs. the control, 2, 5, and 10s -Gz conditions (109+/-1.1 vs. 102+/-1.8, 100+/-2.0, 97+/-1.1 and 101+/-1.1, bpm, respectively; p<0.05)., Conclusions: HR, unlike BP, increases briskly across all preceding -Gz time conditions, adapting within the initial baroreflex-compensatory time frame typically expected for +Gz exposures. These results suggest there may be a threshold effect for HR response. Consequently, vasoconstrictor response is a critical adaptive mechanism during +Gz when preceded by long (>10 s) -Gz exposures.

The probability that a dose of ionizing radiation kills a cell is about 10,000 times the probability that the cell will be transformed to malignancy. On the other hand, the number of cells killed required to significantly impact health is about 10,000 times the number that must be transformed to cause a late malignancy. If these two risks, cell killing and malignant transformation, are about equal, then the risk that occurs during a mission is more significant than the risk that occurs after a mission. The latent period for acute irradiation effects (cell killing) is about 2-4 weeks; the latent period for malignancy is 10-20 years. If these statements are approximately true, then the impact of cell killing on health in the low-gravity environment of space flight should be examined to establish an estimate of risk. The objective of this study is to synthesize data and conclusions from three areas of space biology and environmental health to arrive at rational risk assessment for radiations received by spacecraft crews: (1) the increased physiological demands of the space flight environment; (2) the effects of the space flight environment on physiological systems; and (3) the effects of radiation on physiological systems. One physiological system has been chosen: the immune response and its components, consisting of myeloid and lymphoid proliferative cell compartments. Best-case and worst-case scenarios are considered. In the worst case, a doubling of immune-function demand, accompanied by a halving of immune capacity, would reduce the endangering dose to a crew member to around 1 Gy.

Background: It has been known since 1953 that pre-exposure to less than +1 Gz will reduce subsequent +Gz-tolerance. With few exceptions, during operational flying, the transition from hypogravity to hypergravity involves roll as well as pitch rotation. We examined the effect of roll vs. pitch rotation while undergoing transition from hypogravity to +1 Gz on a tilt table., Methods: Twelve subjects (28-47 yr old) were rotated at 45 degrees x s(-1) from head-up (HU) at 15 degrees relative to gravitational vertical to 135 degrees head-down (HD) and back to the HU position after different HD dwell times. HD dwell times were set at 7, 15, and 30 s. The subject was rotated about the interaural axis (pitch) and about the naso-occipital axis (roll). Both the HD dwell times and axes of rotation were randomized within and across subjects. BP and heart rate were recorded during the HU-HD-HU maneuver., Results: Analysis of variance, repeated measure design revealed that the rate and magnitude of BP decrease induced by the HD to HU maneuver is significantly higher (p < 0.01) in roll than in pitch during all HD dwell times. The decrease of BP at 7s is significantly (p < 0.01) higher than at 15s and 30s. Heart rate increases significantly higher (p < 0.01) in pitch than in roll at 7s-dwell time., Conclusion: Our results suggest that the compensatory mechanism to orthostatic stress is more efficient in response to pitch than roll rotation. This is reflected from the findings that the mean magnitude of OH (orthostatic hypotension) and the rate of BP decrease induced by the HD-HU maneuver is significantly greater in roll rotation than pitch rotation. The mean HR increase post HD-HU rotation is significantly higher in the pitch than the roll rotation. The significant rate of BP decrease during HD-HU roll rotation could have important implications for maintaining G-tolerance and spatial orientation during subsequent exposure to hypergravity.

Background: Responses of pituitary concentrations of vasopressin (AVP) and oxytocin (OT) during spaceflight have been variable, possibly due to differences in flight conditions or in age and strain of flight animals., Methods: We reviewed findings of three space-flights of varying flight and recovery durations in which rats of different ages and strains were used. Male rats ranging in weight from 248-396 g were flown in space for 7-14 d. Flight animals were then compared with vivarium controls and synchronous controls. Parallel ground-based studies (hypergravity and simulated hypogravity) were conducted., Results: Pituitary content of AVP was significantly (p < or = 0.05) decreased by spaceflight (6.3 +/- 0.3 micrograms.mg-1 protein in flight vs. 8.3 +/- 0.5 micrograms.mg-1 protein in vivarium). OT content was also reduced during spaceflight (4.3 +/- 0.2 micrograms.mg-1 protein in flight vs. 6.1 +/- 0.3 micrograms.mg-1 protein in vivarium). Vivarium and synchronous control rats showed no difference in pituitary contents. Flight duration or recovery times did not appear to influence pituitary hormone contents. Strain of rat had an effect on content but not on responses to spaceflight. Age of animals confounded the response to spaceflight: pituitary contents of AVP and OT were not altered in young animals (< or = 60 d old). Hindlimb suspended animals showed no difference in AVP but OT content was decreased. Ground-based exposure to hypergravity (2 G) did not alter content of AVP or OT in young animals., Conclusions: Decreases in pituitary content of AVP and OT with spaceflight may be due to a variety of factors unique to the microgravity environment. Differences between studies may be due in part to differences in size and age of rats used.

Background: A previous study revealed that exposure of rats to microgravity for 14 d on Cosmos 2044 reduced production of testosterone by > 80%, although spermatogenesis remained essentially normal., Methods: To ascertain if testicular function was altered in hypergravity, 60-d-old rats were randomly assigned to 2 groups (10 per group) and subjected to 14 d of centrifugation to expose them to a total of 2G, or held at unit gravity in similar cages without centrifugation (control)., Results: After 14 d, body weight of 2G rats was essentially unchanged, whereas that of control rats had increased; 310 vs. 377 g (p < 0.05). Testes weight, production and secretion of testosterone, diameters of seminiferous tubules and their lumina, data from subjective evaluation of spermatogenesis, and counts of homogenization-resistant spermatids all were similar for 2G and control rats., Conclusion: It was concluded that exposure of male rats to 2G for 14 d had no major effect on testicular function whereas, based on earlier studies, exposure to microgravity (< 10(-3) x gravity) for 11-14 d suppressed production of testosterone by Leydig cells and reduced concentrations of anabolic steroids available to peripheral tissues.

Background: While life science data dealing with effects of hypogravity are accumulating, relatively little is known about the effects of hypergravity at the level of either the whole animal or the individual cell. The purpose of this experiment was to compare data collected on cells of anterior pituitaries from animals centrifuged at 2G using an experimental design that was identical to that of a spaceflight experiment performed in 1989., Hypothesis: Centrifugation of the animal at 2G for 14 d alters the function and morphology of cells of the anterior pituitary in subsequent in vitro tests at 1G., Methods: Intact rats were centrifuged at twice Earth's gravity for 14 d in a specially designed animal centrifuge as part of the Cosmos 2G study. This study was designed to replicate a previous spaceflight experiment so that direct comparisons between hyper- (centrifugation, 2G) and hypogravity (spaceflight, 0.001G) could be made. Anterior pituitary cells were then evaluated for cell function and morphology in a variety of post-flight tests., Results: Growth hormone cells from centrifuged animals released less bioactive, but not immunoreactive, growth hormone (GH) than cells from non-centrifuged animals. This was also true for GH released in response to provocative stimulation by a synthetic peptide (growth hormone releasing hormone, GHRH) that causes GH release after binding to cell membrane receptors. Cell morphology was also different between cells from centrifuged and control animals; cells in the experimental group were smaller and less granulated. However, another type of hormone-producing cell contained in these preparations, viz. prolactin cells, was not affected by centrifugation., Conclusions: Centrifugation of animals for 14 d alters both the in vitro release of GH and GH cell morphology relative to corresponding controls from non-centrifuged animals. Because prolactin cells are not affected by centrifugation, the response is specific to the GH cell.

Background: Spaceflight causes a number of physiological changes in the human body. Most would consider space travel to be a stressful event even for well-trained astronauts. Should this be true, pituitary gonadotrophins (mainly LH) and testicular androgens, like testosterone (T), should decrease inflight in male astronauts. We therefore hypothesized that lowered testicular androgen levels might occur in men during spaceflight, due to stress-dependent lowered LH concentrations., Methods: In order to test this hypothesis, on different day pre-, in- and postflight we assayed wake-time salivary and urinary T in four astronauts, as well as wake-time plasma levels of adrenocorticotropin (ACTH), cortisol (CS), LH, T and its peripherally active metabolite 3-alpha-diol glucuronide (3ADG). In order to compare clinical to subjective data, all 7 male crewmembers anonymously answered a daily questionnaire from pre- to postflight asking them to self-rate sexual drive and potency, muscle strength and mood., Results: Salivary, urinary and plasma T, as well as 3ADG, decreased during flight, while LH unexpectedly increased inflight (p < 0.05). A parallel decrease in sexual drive was observed (p < 0.05). A dramatic recovery of salivary T was found on R + 1., Conclusions: This was the first time that spaceflight was demonstrated to cause temporary, still dramatic hypoandrogenism which was not due to blunted pituitary gonadotrophin secretion. The cause for hypoandrogenism is unknown but it may depend on fluid shift affecting testicular function or androgen distribution in various body compartments.

Background: The effects of exercise on postural control during walking were evaluated following exposure to head-down bed rest (BR)., Methods: Two groups of male subjects (N = 18, mean age = 21.4 yr +/- SE 1.0) were exposed to 5 d of 6 degrees head-down bed rest. The experimental group (E) exercised 90 min.d-1 (n = 12 subjects) during the BR while the control group received no intervention (n = 6). The exercise treatment consisted of a combination of isotonic and isokinetic lower extremity exercise training. Electromyographic (EMG) activity in the tibialis anterior, gastrocnemius, vastus lateralis, and biceps femoris was measured during walking before and after BR., Results: Following BR, EMG activity increased in both test subject groups for all muscles (p < 0.05). However, there were no significant differences in EMG activity between the C and E groups either before or after BR., Conclusions: These data suggest that the ability of the postural control system to adjust to the gravitational environment was compromised as a result of BR. In addition, we conclude that the exercise protocol used was not an effective countermeasure to the alterations in the postural control system.

The human species is rapidly expanding. Barring global catastrophe and unnatural constraints, it will, in a brief time on the scale of natural history, fill the uttermost reaches of the solar system. The beachhead established by President Kennedy's lunar program will lead to lunar, Martian and free space settlements in the next century. In a single generation of those who call them home, the constant 9.81 m.s-2 pull of Earth's gravity, which has influenced the evolution and development of terrestrial life forms for billions of years, will fade from common experience. Miogravity syndrome, a prognosticated complex arising in reduced gravity environments such as the surfaces of the Moon and Mars and principally encompassing muscle atrophy, cardiovascular deconditioning and bone demineralization, stands to replace physics and rocketry as the fundamental challenge of interplanetary astronautics. Mirroring our past few million years of changing climate and resources, the mobility of humans between diverse gravitational environments on the high frontier will critically depend on our ability to adapt. Tomorrow, as ever, a mushrooming penchant for toolmaking will spearhead the human career.

Background: We studied whether microgravity influences horizontal and vertical vestibulo-ocular reflex (VOR), and what the otolith contributes to VOR in the absence of gravity, in six cosmonauts during and after space missions., Method: VOR was elicited by active yaw and roll head movement at a frequency of about 0.2 Hz., Results: The various individual quantitative changes (increase, decrease, and left-right asymmetry) found in the horizontal VOR evoked by yaw head movements during the adaptation period to microgravity suggested central reprogramming of mechanisms controlling VOR; i.e., a non-specific effect of microgravity on VOR. At the same time, horizontal and vertical VOR's were recorded during roll head movements, which were not obvious before flight. In the consmonaut who participated in a long-term flight, the increased activity of vertical canals turned to unidirectional (downward) eye movements, independent of the head movement direction, lasting during the whole mission. These VOR changes probably resulted from the absent adequate otolith stimulation and reduced otolith influence upon semicircular canal function., Conclusions: Thus, a specific effect of microgravity on VOR was observed during roll head movements, when the interaction between semicircular canals and otoliths should be more pronounced, mainly in the vertical plane. The stability of the "space" pattern of interactions in the readaptation period depended on the time spent in microgravity. We suggest that in visual-vestibular interactions revealed in VOR evoked by head movements with open eyes, vision dominates when a conflict arises between "space" and "terrestrial" patterns of sensory interactions.

Supporting the mass of a protective suit and portable life support system (PLSS) will impose an energy requirement on planetary astronauts. To design extravehicular protective equipment for planetary missions, scientists must learn more about human physical capabilities while load-carrying in reduced gravities. In this study, an underwater treadmill and weighting system were used to simulate reduced-gravity locomotion while load-carrying. The test matrix included 3 gravity levels, 6 subjects, 2 locomotion speeds, and a range of load sizes. Energy expenditure, calculated from measured oxygen consumption, is positively correlated with gravity level, speed, and load size. The data are used to project that individuals in average physical condition will be able to walk for 8 h on the Moon while carrying up to 170% of their body mass without undue fatigue, and on Mars with up to 50% of their body mass. These approximate limits, especially for Martian gravity, may prove quite a challenge for designers of advanced protective systems. Requirements for regenerable and non-venting PLSS components have been driving the total projected masses of advanced PLSSs increasingly higher, perhaps beyond what is reasonable to carry. However, the larger mass can be beneficial in maintaining bone mass. Using Whalen's model (1988), the daily planetary walking times required to maintain bone mass were calculated for a range of carried load sizes. The calculated times were unattainably high, suggesting that some combination of loads carrying and supplemental bone maintenance measures will likely be required to maintain bone mass in reduced gravity environments.

The hypobaric chamber is designed as a teaching aid in providing orientation for some of the physiological stresses in flight. Reactions during chamber training vary from mild ear block to neurocirculatory collapse. This is a retrospective study on reactions from 1986-94 in the hypobaric chamber training unit at King Hussien Medical Centre in Jordan; 39 cases were reported among 705 trainees in a 12-person rectangular hypobaric chamber. We analyzed the various reactions according to type, severity and altitude of occurrence. The most common reactions were found to be ear block (65%) and sinus block (25%). These were treated on the spot and followed for 48 h without sequelae. We did not have any moderate or severe reaction; we found that all reactions were minor, which reflects the efficacy of safety measures taken prior to and during training.

Human space missions have shown that human spaceflight is associated with a loss of body protein. Specific changes include a loss of lean body mass, decreased muscle mass in the calves, decreased muscle strength, and changes in plasma proteins and amino acids. The major muscle loss is believed to be associated with the antigravity (postural) muscle. The most significant loss of protein appears to occur during the first month of flight. The etiology is believed to be multifactorial with contributions from disuse atrophy, undernutrition, and a stress type of response. This article reviews the results of American and Russian space missions to investigate this problem in humans, monkeys, and rats. The relationship of the flight results with ground-based models including bedrest for humans and hindlimb unweighting for rats is also discussed. The results suggest that humans adapt to spaceflight much better than either monkeys or rats.

From the basic impact of nutrient intake on health maintenance to the psychosocial benefits of mealtime, the role of nutrition in space is evident. In this discussion, dietary intake data from three space programs, Apollo, Space Shuttle, and Skylab, are presented. Data examination reveals that energy and fluid intakes are almost always lower than predicted. Nutrition in space has many areas of impact, including provision of required nutrients and maintenance of endocrine, immune, and musculoskeletal systems. Long-duration missions will require quantitation of nutrient requirements for maintenance of health and protection against the effects of microgravity. Psychosocial aspects of nutrition will also be important for more productive missions and crew morale. Realization of the full role of nutrition during spaceflight is critical for the success of extended-duration missions. Research conducted to determine the impact of spaceflight on human physiology and subsequent nutritional requirements will also have direct and indirect applications in Earth-based nutrition research.

A quarter of a century ago men stepped upon the lunar surface and established the possibility of human expansion beyond Earth. When humans return to the moon to occupy it with greater permanency, an applied lunar biological laboratory would provide a means of conducting experiments on the long-term effects of fractional gravity in animals and plants and provide necessary data to enhance the health, safety and well-being of lunar workers and inhabitants. In-depth studies can go beyond zero-g observations, on-orbit centrifuge studies, and ground-based research providing important insight into continuous 1/6-g effects on biological systems. Studies concentrating on development, gravity sensing, and adaptation/readaptation would provide preliminary data on whether long-term fractional gravity is detrimental or compromising to fundamental biological function. Food production research in 1/6-g would provide important information for on site application to improve the yield and quality of food (animal and plant) produced in the unique lunar environment. The purpose of this paper is to discuss some examples of the major gravitational biology areas that could be studied on the moon and applied to lunar population needs utilizing lunar biological facilities and continuous fractional gravity.