Head-down Bed Rest Research Articles

Retinal blood vessel diameter changes with 60-day head-down bedrest are unaffected by antioxidant nutritional cocktail.

Long-term human spaceflight can lead to cardiovascular deconditioning, but little is known about how weightlessness affects microcirculation. In this study, we examined how the retinal microvessels and cerebrovascular regulation of 19 healthy male participants responded to long-term head-down bedrest (HDBR), an earth-based analog for weightlessness. In addition, we examined whether an anti-inflammatory/antioxidant cocktail could prevent the vascular changes caused by HDBR. In all study participants, we found a decrease in retinal arteriolar diameter by HDBR day 8 and an increase in retinal venular diameter by HDBR day 16. Concurrently, blood pressure at the level of the middle cerebral artery and the cerebrovascular resistance index were higher during HDBR, while cerebral blood flow velocity was lower. None of these changes were reversed in participants receiving the anti-inflammatory/antioxidant cocktail, indicating that this cocktail was insufficient to restore the microvascular and cerebral blood flow changes induced by HDBR.

Artificial gravity: an effective countermeasure for microgravity-induced headward fluid shift?

Long-duration spaceflight is associated with pathophysiological changes in the intracranial compartment hypothetically linked to microgravity-induced headward fluid shift. This study aimed to determine whether daily artificial gravity (AG) sessions can mitigate these effects, supporting its application as a countermeasure to spaceflight. Twenty-four healthy adult volunteers (16 men) were exposed to 60 days of 6° head-down tilt bed rest (HDTBR) as a ground-based analog of chronic headward fluid shift. Subjects were divided equally into three groups: no AG (control), daily 30-min intermittent AG (iAG), and daily 30-min continuous (cAG). Internal carotid artery (ICA) stroke volume (ICASV), ICA resistive index (ICARI), ICA flow rate (ICAFR), aqueductal cerebral spinal fluid flow velocity (CSFV), and intracranial volumetrics were quantified at 3 T. MRI was performed at baseline, 14 and 52 days into HDTBR, and 3 days after HDTBR (recovery). A mixed model approach was used with intervention and time as the fixed effect factors and the subject as the random effect factor. Compared with baseline, HDTBR was characterized by expansion of lateral ventricular, white matter, gray matter, and brain + total intracranial cerebral spinal fluid volumes, increased CSFv, decreased ICASV, and decreased ICAFR by 52 days into HBTBR (All Ps < 0.05). ICARI was only increased 14 days into HDTBR (P < 0.05). Neither iAG nor cAG significantly affected measurements compared with HDTBR alone, indicating that 30 min of daily exposure was insufficient to mitigate the intracranial effects of headward fluid shift. Greater AG session exposure time, gravitational force, or both are suggested for future countermeasure research.NEW & NOTEWORTHY Brief exposure to continuous or intermittent artificial gravity via short-arm centrifugation was insufficient in mitigating the intracranial pathophysiological effects of the headward fluid shift simulated during head-down tilt bed rest (HDTBR). Our results suggest that greater centrifugation session duration, gravitational force, or both may be required to prevent the development of spaceflight-associated neuro-ocular syndrome and should be considered in future ground-based countermeasure studies.

Key Anabolic Markers in Human M. Soleus after 21-Day Head-Down Tilt Bedrest

Prolonged bed rest can have a significant negative effect on skeletal muscle, leading to muscle wasting and reduced strength. This process can occur in as little as 10 days in healthy individuals, with the loss of muscle mass and strength being particularly pronounced during the first week of immobilization. Head-down tilt bed rest (HDT) is a method used to simulate the physiological changes that occur in weightlessness during spaceflight. This technique involves lying in bed with the head tilted downward. This paper is dedicated to the analysis of key anabolic markers of the soleus muscle during 21 days of HDT BR. The HDT BR experiment was conducted at the Institute of Biomedical Problems, Russian Academy of Sciences. Six healthy male volunteers, aged 25–35 years, were subjected to 21 days of strict bed rest with a tilt angle of –6°. A needle biopsy of the m.soleus was performed using the Bergström method before the start of HDT BR and on day 21 of HDT BR. The biopsy material was immediately frozen in liquid nitrogen for further Western blot and PCR analysis. Examination of mTORC1 substrates showed a significant decrease in p70 and 4EBP1 phosphorylation after HDT BR. We also observed a significant decrease in the phosphorylation of another ribosomal kinase, p90RSK, a significant increase in eEF2 phosphorylation and an increase in eEF2k mRNA expression. In addition, the phosphorylation of AMPK and its substrate ACC decreased after HDT BR. The data obtained in this work support the hypothesis that a decrease in protein synthesis, together with an increase in proteolysis, contributes to the development of human m. soleus atrophy after 21 days of HDT BR.

Biological Sex Modestly Influences the Impact of Long Duration Bed Rest on Human Sympathetic Neurocirculatory Regulation

Our understanding regarding the impact of simulated microgravity on sympathetic neurocirculatory regulation, and the modulatory effects of biological sex, remain incomplete. Through retrospective analysis of two long-duration bed rest trials, this study investigated the impact of 60 days of -6° head-down bed rest (HDBR) on the transduction of integrated muscle sympathetic nerve activity (MSNA; peroneal microneurography) into mean arterial pressure (MAP; Finometer) in healthy females ( n = 12, 25-40 years) and males ( n = 13, 21-42 years). Signal averaging quantified sympathetic transduction for 12 cardiac cycles (ECG) following integrated MSNA bursts. The transduction of integrated MSNA bursting patterns was studied based on the overall response, temporal burst firing patterns (singlet, doublet, and triplet+), and burst amplitude (binned into quartiles: Q1-Q4). Data are reported as mean (SD) for a 5-minute baseline period pre-HDBR and post-HDBR. Statistical analysis included mixed-effect analyses with post-hoc t-tests. In the pooled analyses, HDBR reduced the overall MAP transduction response to integrated MSNA bursts (pre-HDBR: 1.4 ± 0.5 mmHg, post-HDBR: 1.1 ± 0.4 mmHg; P = 0.003). This stemmed from attenuated MAP transduction responses to small- and medium-sized bursts (i.e., Q1-Q3) but there was no effect of HDBR on the largest bursts (i.e., Q4: pre-HDBR: 2.2 ± 0.9 mmHg, post-HDBR: 2.1 ± 0.9 mmHg; P = 0.59). HDBR did not affect the transduction response to singlets (P = 0.23), but HDBR reduced the MAP transduction responses to doublets and triplets+ (both P &lt; 0.03). HDBR did not affect the reduction in MAP during non-bursting periods (pre-HDBR: -0.5 ± 0.2 mmHg, post-HDBR: -0.4 ± 0.2 mmHg; P = 0.17). When stratifying the analyses by sex, we observed that HDBR reduced the overall MAP transduction response to integrated MSNA bursts more so in males (P &lt; 0.01) than females (P = 0.14). Conversely, HDBR did not affect the MAP reductions following non-bursting periods in males (P = 0.53), but in females the reduction in MAP following non-bursting periods was less after HDBR, particularly for cardiac cycles 5 to 7 (pre-HDBR: -0.8 ± 0.5 mmHg, post-HDBR: -0.5 ± 0.3 mmHg; P = 0.03). These data suggest that 60 days of HDBR attenuates sympathetic neurocirculatory regulation during baseline conditions, with a modest influence of biological sex. This work was supported by the Canadian Space Agency, Centre National d'Etudes Spatiales, European Space Agency, National Aeronautics and Space Administration, Institute of Aerospace Medicine of the German Aerospace Center (DLR), Fond Européen de Développement Régional (FEDER) and the Natural Sciences and Engineering Research Council of Canada (NSERC). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Long-duration bed rest augments sympathetic neurovascular responses to simulated orthostatic stress among females

Our understanding of the impact of long-duration head-down bed rest (HDBR) on sympathetic neurovascular regulation during orthostatic stress remains incomplete. Through retrospective analysis of the WISE-2005 long-duration bed rest trial, this study aimed to investigate the impact of 60 days of -6° HDBR on the transduction of integrated muscle sympathetic nerve activity (MSNA; peroneal microneurography) into total peripheral resistance (TPR; Finometer Modelflow) responses during rest and graded lower body negative pressure (LBNP; -20, -30, and -45 mmHg). Signal averaging quantified sympathetic transduction for 12 cardiac cycles (ECG) following integrated MSNA bursts in healthy females ( n = 12; 25-40 years). Mixed-effects modeling and post-hoct-tests assessed the impact of HDBR on sympathetic transduction during rest (5-min) and graded LBNP (3-min per level). Data are presented as mean ± SD. Long-duration HDBR did not affect resting total MSNA (pre-HDBR: 909 ± 368 AU/min, post-HDBR: 910 ± 254 AU/min; p = 0.999). HDBR did not affect total MSNA responses to -20 mmHg LBNP (pre-HDBR: 1430 ± 599 AU/min, post-HDBR: 1823 ± 433 AU/min), -30 mmHg LBNP (pre-HDBR: 1574 ± 549 AU/min, post-HDBR: 1924 ± 587 AU/min), or -45 mmHg LBNP (pre-HDBR: 1950 ± 819 AU/min, post-HDBR: 2328 ± 880 AU/min; p = 0.191). HDBR did not affect resting sympathetic transduction to TPR (pre-HDBR: 0.002 ± 0.16 mmHg/L/min, post-HDBR: -0.091 ± 0.12 mmHg/L/min; p = 0.296). However, HDBR augmented TPR transduction responses to graded LBNP (HDBR-by-LBNP interaction: p = 0.050). Pre-HDBR, TPR transduction responses were unchanged with graded LBNP (all p &gt; 0.05). In contrast, post-HDBR, TPR transduction responses increased progressively with graded LBNP (rest: -0.09 ± 0.12 mmHg/L/min, -20 mmHg: 0.22 ± 0.31 mmHg/L/min, -30 mmHg: 0.30 ± 0.34 mmHg/L/min, -45 mmHg: 0.44 ± 0.12 mmHg/L/min; all p &lt; 0.005). The same effect of HDBR was observed when sympathetic transduction of mean arterial pressure was analyzed (data not shown). These data suggest that long-duration HDBR augments sympathetic neurovascular responses to integrated MSNA bursts during orthostatic stress among females. This work was supported by the Canadian Space Agency, the French “Centre National d’Etudes Spatiales”, the European Space Agency, and the National Aeronautics and Space Administration of the USA. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Key Anabolic Markers in Human Soleus Muscle after 21-Day Head-Down Tilt Bed Rest

Key Anabolic Markers in Human Soleus Muscle after 21-Day Head-Down Tilt Bed Rest

Potential Biomarkers of Resilience to Microgravity Hazards in Astronauts.

Space exploration exposes astronauts to the unique environment of microgravity, which poses significant health challenges. Identifying biomarkers that can predict an individual's resilience to the stressors of microgravity holds great promise for optimizing astronaut selection and developing personalized countermeasures. This narrative review examines the principal health risks associated with microgravity and explores potential biomarkers indicative of resilience. The biomarkers being evaluated represent a broad spectrum of physiological domains, including musculoskeletal, neurological, immunological, gastrointestinal, cardiovascular, and cutaneous systems. Earth-based microgravity analogs, such as dry immersion and head-down tilt bed rest, may provide valuable platforms to validate candidate biomarkers. However, biomarker sensitivity and specificity must be further evaluated to ensure efficacy and reliability. Establishing a panel of biomarkers predictive of resilience to microgravity-induced health risks would significantly enhance astronaut health and mission success, especially for long-duration exploration missions. Insights gained may also translate to health conditions on Earth characterized by reduced physical activity and mechanical loading.

Dynamic changes in perivascular space morphology predict signs of spaceflight-associated neuro-ocular syndrome in bed rest

During long-duration spaceflight, astronauts experience headward fluid shifts and expansion of the cerebral perivascular spaces (PVS). A major limitation to our understanding of the changes in brain structure and physiology induced by spaceflight stems from the logistical difficulties of studying astronauts. The current study aimed to determine whether PVS changes also occur on Earth with the spaceflight analog head-down tilt bed rest (HDBR). We examined how the number and morphology of magnetic resonance imaging-visible PVS (MV-PVS) are affected by HDBR with and without elevated carbon dioxide (CO2). These environments mimic the headward fluid shifts, body unloading, and elevated CO2 observed aboard the International Space Station. Additionally, we sought to understand how changes in MV-PVS are associated with signs of Spaceflight Associated Neuro-ocular Syndrome (SANS), ocular structural alterations that can occur with spaceflight. Participants were separated into two bed rest campaigns: HDBR (60 days) and HDBR + CO2 (30 days with elevated ambient CO2). Both groups completed multiple magnetic resonance image acquisitions before, during, and post-bed rest. We found that at the group level, neither spaceflight analog affected MV-PVS quantity or morphology. However, when taking into account SANS status, persons exhibiting signs of SANS showed little or no MV-PVS changes, whereas their No-SANS counterparts showed MV-PVS morphological changes during the HDBR + CO2 campaign. These findings highlight spaceflight analogs as models for inducing changes in MV-PVS and implicate MV-PVS dynamic compliance as a mechanism underlying SANS. These findings may lead to countermeasures to mitigate health risks associated with human spaceflight.

Myths and Methodologies: Understanding the health impact of head down bedrest for the benefit of older adults and astronauts. Study protocol of the Canadian Bedrest Study.

Weightlessness during spaceflight can harm various bodily systems, including bone density, muscle mass, strength and cognitive functions. Exercise appears to somewhat counteract these effects. A terrestrial model for this is head-down bedrest (HDBR), simulating gravity loss. This mirrors challenges faced by older adults in extended bedrest and space environments. The first Canadian study, backed by the Canadian Space Agency, Canadian Institutes of Health Research, and Canadian Frailty Network, aims to explore these issues. The study seeks to: (1) scrutinize the impact of 14-day HDBR on physiological, psychological and neurocognitive systems, and (2) assess the benefits of exercise during HDBR. Eight teams developed distinct protocols, harmonized in three videoconferences, at the McGill University Health Center. Over 26days, 23 participants aged 55-65 underwent baseline measurements, 14days of -6° HDBR, and 7days of recovery. Half did prescribed exercise thrice daily combining resistance and endurance exercise for a total duration of 1h. Assessments included demographics, cardiorespiratory fitness, bone health, body composition, quality of life, mental health, cognition, muscle health and biomarkers. This study has yielded some published outcomes, with more forthcoming. Findings will enrich our comprehension of HDBR effects, guiding future strategies for astronaut well-being and aiding bedrest-bound older adults. By outlining evidence-based interventions, this research supports both space travellers and those enduring prolonged bedrest.

Development of optic disc edema during 30 days of hypercapnic head-down tilt bed rest is associated with short sleep duration and blunted temperature amplitude.

Sleep and circadian temperature disturbances occur with spaceflight and may, in part, result from the chronically elevated carbon dioxide (CO2) levels on the international space station. Impaired sleep may contribute to decreased glymphatic clearance and, when combined with the chronic headward fluid shift during actual spaceflight or the spaceflight analog head-down tilt bed rest (HDTBR), may contribute to the development of optic disc edema. We determined if strict HDTBR combined with mildly elevated CO2 levels influenced sleep and core temperature and was associated with the development of optic disc edema. Healthy participants (5 females) aged 25-50 yr, underwent 30 days of strict 6° HDTBR with ambient Pco2 = 4 mmHg. Measures of sleep, 24-h core temperature, overnight transcutaneous CO2, and Frisén grade edema were made pre-HDTBR, on HDTBR days 4, 17, 28, and post-HDTBR days 4 and 10. During all HDTBR time points, sleep, core temperature, and overnight transcutaneous CO2 were not different than the pre-HDTBR measurements. However, independent of the HDTBR intervention, the odds ratios {mean [95% confidence interval (CI)]} for developing Frisén grade optic disc edema were statistically significant for each hour below the mean total sleep time (2.2 [1.1-4.4]) and stage 2 nonrapid eye movement (NREM) sleep (4.8 [1.3-18.6]), and above the mean for wake after sleep onset (3.6 [1.2-10.6]) and for each 0.1°C decrease in core temperature amplitude below the mean (4.0 [1.4-11.7]). These data suggest that optic disc edema occurring during HDTBR was more likely to occur in those with short sleep duration and/or blunted temperature amplitude.NEW & NOTEWORTHY We determined that sleep and 24-h core body temperature were unaltered by 30 days exposure to the spaceflight analog strict 6° head-down tilt bed rest (HDTBR) in a 0.5% CO2 environment. However, shorter sleep duration, greater wake after sleep onset, and lower core temperature amplitude present throughout the study were associated with the development of optic disc edema, a key finding of spaceflight-associated neuro-ocular syndrome.

Effects of 30 days bed rest and exercise countermeasures on PBMC bioenergetics.

Altered mitochondrial function across various tissues is a key determinant of spaceflight-induced physical deconditioning. In comparison to tissue biopsies, blood cell bioenergetics holds promise as a systemic and more readily accessible biomarker, which was evaluated during head-down tilt bed rest (HDTBR), an established ground-based analog for spaceflight-induced physiological changes in humans. More specifically, this study explored the effects of HDTBR and an exercise countermeasure on mitochondrial respiration in peripheral blood mononuclear cells (PBMCs). We subjected 24 healthy participants to a strict 30-day HDTBR protocol. The control group (n = 12) underwent HDTBR only, while the countermeasure group (n = 12) engaged in regular supine cycling exercise followed by veno-occlusive thigh cuffs post-exercise for 6 h. We assessed routine blood parameters 14 days before bed rest, the respiratory capacity of PBMCs via high-resolution respirometry, and citrate synthase activity 2 days before and at day 30 of bed rest. We confirmed PBMC composition by flow cytometry. The change of the PBMC maximal oxidative phosphorylation capacity (OXPHOS) amounted to an 11% increase in the countermeasure group, while it decreased by 10% in the control group (p = 0.04). The limitation of OXPHOS increased in control only while other respiratory states were not affected by either intervention. Correlation analysis revealed positive associations between white blood cells, lymphocytes, and basophils with PBMC bioenergetics in both groups. This study reveals that a regular exercise countermeasure has a positive impact on PBMC mitochondrial function, confirming the potential application of blood cell bioenergetics for human spaceflight.

Effect of 15 days -6° head-down bed rest on microbial communities of supragingival plaque in young men.

The microgravity environment astronauts experience during spaceflight can lead to an increased risk of oral diseases and possible changes in oral microecology. In this study, we aimed to assess changes in the microbial community of supragingival plaques to explore the effects of spaceflight microgravity environment on oral microecology. Sixteen healthy male volunteers were recruited, and supragingival plaque samples were collected under -6° head-down bed rest (HDBR) at five-time points: day 1 before HDBR; days 5, 10, and 15 of HDBR; and day 6 of recovery. Bacterial genomic DNA was sequenced using gene sequencing technology with 16S ribosomal ribonucleic acid V3-V4 hypervariable region amplification and the obtained data were analyzed bioinformatically. Alpha diversity analysis showed a significant increase in species richness in supragingival plaque samples on day 15 of HDBR compared with that at pre-HDBR. Beta diversity analysis revealed that the community composition differed among the groups. Species distribution showed that, compared with those at pre-HDBR, the relative abundances of Corynebacterium and Aggregatibacter increased significantly during HDBR, while those of Veillonella, Streptococcus, and Lautropia decreased significantly. Moreover, compared with those at pre-HDBR, the relative abundance of Leptotrichia increased significantly on day 6 of recovery, whereas the relative abundances of Porphyromonas and Streptococcus decreased significantly. Network analysis showed that the interaction relationship between the dominant genera became simpler during HDBR, and the positive and negative correlations between them showed dynamic changes. Phylogenetic investigation of communities by reconstruction of unobserved states analysis showed that the amino acid metabolism function of plaque microorganisms was more enriched during HDBR. In summary, in a 15-day simulated microgravity environment, the diversity, species distribution, interaction relationship, and metabolic function of the supragingival plaque microbial community changed, which suggests that microgravity may affect the oral microecosystem by changing the balance of supragingival plaque microbial communities and further leading to the occurrence and development of oral diseases.

Quantitative ultrasound image assessment of the optic nerve subarachnoid space during 90-day head-down tilt bed rest

The elevation in the optic nerve sheath (ONS) pressure (ONSP) due to microgravity-induced headward fluid shift is the primary hypothesized contributor to SANS. This longitudinal study aims to quantify the axial plane of the optic nerve subarachnoid space area (ONSSA), which is filled with cerebrospinal fluid (CSF) and expands with elevated ONSP during and after head-down tilt (HDT) bed rest (BR). 36 healthy male volunteers (72 eyes) underwent a 90-day strict 6° HDT BR. Without obtaining the pre-HDT data, measurements were performed on days 30, 60, and 90 during HDT and at 6 recovery time points extended to 180-days (R + 180) in a supine position. Portable B-scan ultrasound was performed using the 12 MHz linear array probe binocularly. The measurements of the ONS and the calculation of the ONSSA were performed with ImageJ 1.51 analysis software by two experienced observers in a masked manner. Compared to R + 180, the ONSSA on HDT30, HDT60, and HDT90 exhibited a consistently significant distention of 0.44 mm2 (95% CI: 0.13 to 0.76 mm2, P = 0.001), 0.45 mm2 (95% CI: 0.15 to 0.75 mm2, P = 0.001), and 0.46 mm2 (95% CI: 0.15 to 0.76 mm2, P < 0.001), respectively, and recovered immediately after HDT on R + 2. Such small changes in the ONSSA were below the lateral resolution limit of ultrasound (0.4 mm) and may not be clinically relevant, possibly due to ONS hysteresis causing persistent ONS distension. Future research can explore advanced quantitative portable ultrasound-based techniques and establish comparisons containing the pre-HDT measurements to deepen our understanding of SANS.

Assessment of the effect of 21-day head-down bed rest on the cardiovascular system by blood protein composition.

Head-down bed rest (HDBR) is one of the models of the physiological effects of weightlessness used, among other things, to assess the effect of hypokinesia on the physiological systems of the human body and, first of all, on the cardiovascular system. The aim of the work was to study the effect of 21 days of HDBR factors on the cardiovascular system based on blood proteomic profile data. It was revealed that HDBR conditions led to an increase in the levels of proteins of the complement and the coagulation cascade systems, platelet degranulation, fibrinolysis, acute phase proteins, post-translational modification of proteins, retinol-binding protein 4 (RBP4), apolipoprotein B, which are associated with cardiovascular diseases, and other proteins that affect the functions of endothelial cells. Blood levels of proteins involved in cytoskeletal remodelling, oxygen transport, heme catabolism, etc. have been shown to decrease during HDBR.

Effects of intermittent seating upright, lower body negative pressure, and exercise on functional tasks performance after head-down tilt bed rest.

Bed rest can be used as a ground-based analog of the body unloading associated with spaceflight. In this study, we determined how strict head-down tilt bed rest affects subjects' performance of functional tests (sit-to-stand, tandem walk, walk-and-turn, dynamic posturography) that challenge astronauts' balance control systems immediately after they return from space. Forty-seven participants were assessed before and a few hours after 30days of 6° head down tilt bed rest at the DLR:envihab facility. During this bed rest study, called SANS-CM, the participants were divided into 4 groups that either a) were positioned in head-down tilt continuously throughout the 30days; b) sat upright for 6h a day; c) were exposed to lower body negative pressure (LBNP) for 6h a day; or d) exercised for 60min and then wore venous-occlusive cuffs for 6h a day. Results showed that strict head-down tilt bed rest caused deficits in performance of functional tasks that were similar to those observed in astronauts after spaceflight. Seated upright posture mitigated these deficits, whereas exercise or LBNP and cuffs partly mitigated them. These data suggest that more direct, active sensorimotor-based countermeasures may be necessary to maintain preflight levels of functional performance after a long period of body unloading.

БИОМЕХАНИЧЕСКИЕ ХАРАКТЕРИСТИКИ ЦИКЛИЧЕСКИХ ЛОКОМОЦИЙ ЧЕЛОВЕКА В ИССЛЕДОВАНИЯХ С РАЗЛИЧНЫМИ НАЗЕМНЫМИ МОДЕЛЯМИ АНТИ- И ОРТОСТАТИЧЕСКОЙ ГИПОКИНЕЗИИ

The paper reports the results of comparative analysis of the kinematic and electromyographic data about human locomotions before and after head-down and orthostatic bed rest of varying length, and successive exposure. We analyzed 3 experimental series, i.e. 21-d head-down bed rest at –6˚(HDBR) reproducing the physiological effects of microgravity, 14-d orthostatic bed rest at +9.6˚ (OBR) reproducing the lunar gravity effects and sequential exposure to 3-d HDBR and 7-d OBR reproducing a mission to the Moon. Locomotions consisted of walking at 60 steps/min and running at the 10 km/h along the horizontal plane, and walking at 3.5 km/h along an inclined plane. All hyporkinesia models unfailingly caused marked changes in kinematics and motor movements. Both types of hypokinesia affected intramuscular and intermuscular coordination as in the gravity-dependent, so flexor muscles of the ankle and knee joint. OBR had a more distinct effect on locomotion biomechanics in comparison with the baseline data. Walking along the inclined plane was characterized by significant changes equally in kinematics and EMG. In addition to changes of the external walking structure, the sequence of 3-d HDBR and 7-d OBR also redistributed the specific input to locomotion of the leg, thigh and specific muscles.

СИСТЕМА ГЕМОКОАГУЛЯЦИИ В НАЗЕМНЫХ ЭКСПЕРИМЕНТАХ, МОДЕЛИРУЮЩИХ ЭФФЕКТЫ КОСМИЧЕСКОГО ПОЛЕТА: ПО МАТЕРИАЛАМ РОССИЙСКИХ ИССЛЕДОВАНИЙ

The review presents the results of studying the hemocoagulation system in Soviet and Russian experiments modeling effects of some spaceflight factors on the human organism. The most adequate models of microgravity are head-down bed rest (BR) and immersion. Effects of g-loads were reproduced by rotation on a centrifuge. In the course of these experiments, the procoagulant, anticoagulant and fibrinolytic activities displayed different trends and dependence on the period of locomotion reduction. In immersion, the procoagulant activity increased, fibrinolytic activity decreased and the anticoagulant potential changed in the either direction. Some data suggest that hypergravity increases the anticoagulant and fibrinolytic activities on the background of hypocoagulation; however, there are also other data suggesting the contrary, i.e. hypergravity leads to hypercoagulation and activation of fibrinolysis. According to investigators, the combination of gravitational loads and limited locomotion decreases the procoagulant activity and increases the fibrinolytic one. Discrepancy between the post-flight and ground-based data is attributed to the impossibility to reproduce in laboratory all the factors that act on the human organism in space flight.

Are changes in muscular strength following head‐down bed rest independently associated with improved cognitive function in older adults? A secondary analysis of a randomized controlled trial

AbstractBackgroundPhysical inactivity is common among older adults and is a risk factor for cognitive decline. Even a brief period of physical inactivity, such as bed rest due to hospitalization, in older adults has significant negative impacts. Exercise is strategy to counter the negative effects of physical inactivity. Exercise‐induced improvements in cardiorespiratory fitness is associated with improved cognitive function. Less is known regarding the contribution of exercise‐induced changes in muscle strength to changes in cognitive function. Thus, we aimed to examine the independent contribution of: 1) change in cardiorespiratory fitness; and 2) change in peak muscle torque of the lower extremity to changes in cognitive function in a randomized controlled trial (RCT) of head‐down bed rest (HDBR) vs. HDBR with exercise in healthy older adults.MethodAn analysis of a non‐blinded, parallel‐group, RCT of 22 healthy older adults (11 males and 11 females) aged 55‐65 years. Participants were randomized to: 1) 14 days of 6° HDBR (CON); or 2) HDBR with daily resistance and aerobic exercise training (EX). Outcome measures were taken at baseline and HDBR completion. The Flanker Inhibitory Control and Attention Task measured executive function. Physical fitness measures included: 1) maximal aerobic capacity (VO2max) using a bicycle ergometry test; and 2) knee extension isokinetic muscular strength (KE) using a Biodex dynamometer. We performed two separate multiple linear regressions to determine whether following 14 days of HDBR: 1) VO2max was associated with Flanker score, after accounting for ΔKE; and 2) KE was associated with Flanker score, after accounting for ΔVO2max. Each model was also adjusted for baseline Flanker score and the baseline physical fitness measure of interest.ResultAt baseline, average Flanker t‐score was 48.33, mean VO2max was 32.527 ml/kg/min, and knee extension strength was 64.472 Nm. VO2max at follow‐up was not significantly associated with Flanker performance (b = 0.232 ± 0.716; p = 0.635; R2 adj. = 0.285). However, greater KE strength was significantly associated with better Flanker performance (b = 2.023 ± 0.389; p = 0.043; R2 adj. = 0.633) at HDBR completion.ConclusionThe maintenance of muscle strength even during brief periods of physical inactivity appears to be critical for cognitive health in older adults.

Exercise training mitigates the deleterious effects of experimental bed rest on intraindividual variability of executive functioning in older adults: A randomised controlled trial

AbstractBackgroundIn older adults, bed rest can occur because of chronic conditions, injury, surgery, or hospitalization. Extreme levels of physical inactivity due to bed rest initiate a downward spiral in several body systems. Exercise is a countermeasure to many of these changes; nonetheless, little is known about the effect of exercise on older adults’ cognition during bed rest. We thus examined the effects of exercise on the intraindividual variability (IIV) of cognitive performance in older adults exposed to 14 days of experimental 6° head‐down bed rest (HDBR) and whether sex moderates its effects. We chose IIV as our outcome measure because it is more sensitive than traditional summary scores of cognitive performance, albeit no studies have explored exercise effects on older adults’ IIV submitted to bed rest.MethodA non‐blinded, parallel‐group, randomised controlled trial. Twenty‐three healthy older adults aged 55‐65 were randomised to: 1) 14 days of HDBR (CON); or 2) 14 days of HDBR with daily aerobic and strength exercise (EX). Data were collected at baseline, HDBR completion, and end of seven‐day‐recovery. The National Institutes of Health Toolbox Cognitive Battery assessed executive function (Flanker Incongruent and Congruent and Dimensional Change Card Sort) and processing speed (Pattern Comparison). IIV was indexed by intraindividual coefficient of variation (ICV) and residual intraindividual standard deviation (R‐ISD), with R‐ISD as our primary measure of interest. Linear mixed models assessed group differences and the moderator role of sex.ResultAt HDBR completion, EX had significantly lower (better) Flanker incongruent ICV (Estimated mean difference = ‐0.10, 95%CI ‐0.19;‐0.003, p = 0.022) and R‐ISD (Estimated mean difference = ‐3.63, 95%CI ‐6.10;‐1.17, p = 0.005) vs. CON. Sex moderated the effect of exercise; females in EX had significantly lower Flanker incongruent ICV vs. CON (Estimated mean difference = ‐0.23; 95%CI ‐0.34;‐0.12, p&lt;0.001). At the end of the seven‐day recovery, EX had significantly lower Flanker incongruent R‐ISD vs. CON (Estimated mean difference = ‐3.11, 95%CI ‐5.70;‐0.052, p = 0.019). Summary scores and processing speed IIV changes were not statistically significant (ps&gt;0.05).ConclusionExercise during HDBR preserved executive functioning, especially in females. Our findings support the delivery of exercises to older adults during bed rest to preserve their cognitive function.

State of the Retina and Optic Nerve in 21-Day Head-Down Tilt Bed Rest

State of the Retina and Optic Nerve in 21-Day Head-Down Tilt Bed Rest