Article

Effect of standing or walking on physiological changes induced by head down bed rest: Implications for spaceflight

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Abstract

To simulate exposure to microgravity and to determine the effectiveness of intermittent exposure to passive and active +1 Gz force (head-to-foot) in preventing head-down bed rest (HDBR) deconditioning, 4 d of 6 degrees HDBR were used. Volunteers were 9 males, 30-50 yr, who performed periodic standing or controlled walking for 2 or 4 h.d-1 in 15-min bouts, one bout per hour, or remained in a continuous HDBR control condition (0 Gz). Standing 4 h (S4) completely prevented, and standing 2 h (S2) partially prevented, decreases in post-HDBR orthostatic tolerance (survival rates with 30 min of upright tilt at 60 degrees). Walking, both 2 h (W2) and 4 h (W4), and S4 attenuated decreases in peak oxygen uptake compared to 0 Gz. Compared to 0 Gz, both S4 and W4 attenuated plasma volume loss during HDBR. Urinary Ca2+ excretion increased over time with HDBR; the quadratic trend for urinary Ca2+, however, was attenuated with W2 and W4. We concluded that various physiological systems benefit differentially from passive +1 Gz or activity in +1 Gz and, in addition to the duration of the stimulus, the number of exposures to postural stimuli may be an important moderating factor.

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... To overcome the lack of high stress and strain, a training regime allowing astronauts to perform reactive jumps should be implemented, as reactive jumps induce the highest ground reaction forces (GRF) and RFD (Ebben et al. 2010). We hypothesized that the short and versatile LRT regime could be a time-efficient countermeasure with compensatory effects on the cardiovascular and the musculoskeletal systems (Smith et al. 2003;Vernikos et al. 1996). The efficacy of the upright LRT scheme was compared to upright standing and to bed rest only using highly standardized measurements that are conducted in all ESA-organized bed rest studies since 2010. ...
... The efficacy of the upright LRT scheme was compared to upright standing and to bed rest only using highly standardized measurements that are conducted in all ESA-organized bed rest studies since 2010. Vernikos et al. (1996) suggested that short-duration bed rest studies could serve as a reliable model for the rapid screening of preventative therapeutic treatments. Hence, in the present study we specifically evaluated the effectiveness of the applied LRT scheme to maintain muscle size, isometric strength, power, and endurance capacity of the leg muscles following 5 days of HDT bed rest. ...
... Though gravitational loading per se (i.e., standing) partially preserved orthostatic tolerance during bed rest (Vernikos et al. 1996), the general consensus is that 'static loading' is ineffective to maintain bone and muscle integrity [e.g., (Lanyon and Rubin 1984)]. The standing condition was implemented as an 'active control condition' to test whether the effects of LRT were related to the exercise per se, or related to the fact that the exercises were performed in the upright (i.e., gravitationally loaded) posture. ...
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The present study evaluated the effectiveness of a short and versatile daily exercise regime, named locomotion replacement training (LRT), to maintain muscle size, isometric strength, power, and endurance capacity of the leg muscles following 5 days of head-down tilt (HDT) bed rest. 10 male subjects (age 29.4 ± 5.9 years; height 178.8 ± 3.7 cm; body mass 77.7 ± 4.1 kg) performed, in random order, 5 days of 6° head-down tilt bed rest (BR) with no exercise (CON), or BR with daily 25 min of upright standing (STA) or LRT. Knee extensor and plantar flexor cross-sectional area (CSA) were reduced by 2-3 % following bed rest (P < 0.01) for CON and STA, yet maintained for LRT. Knee extensor isometric strength (MVC) decreased by 8 % for CON (P < 0.05), was maintained for STA, and increased with 12 % for LRT (P < 0.05). Plantar flexor MVC remained unaltered during the study. Maximum jump height declined (~1.5 cm) for all conditions (P < 0.001). Neural activation and knee extensor fatigability did not change with bed rest. Bone resorption increased during BR and neither LRT nor STA was able to prevent or attenuate this increase. LRT was adequate to maintain muscle size and to even increase knee extensor MVC, but not muscle power and bone integrity, which likely requires more intense and/or longer exercise regimes. However, with only some variables showing significant changes, we conclude that 5 days of BR is an inadequate approach for countermeasure assessments.
... For future long-duration, exploration-class space-flight, such as travel to Mars, it is likely that gravitybased countermeasures will be required (27,39,51,56). Intermittent artificial gravity (IAG), by incorporation of a short-arm centrifuge into the spacecraft, has been suggested as an alternative (4,26,40,(43)(44)(45)(46)56) to continuous artificial gravity (CAG), provided by spinning the entire spacecraft or a tethered rotating spacecraft (27,39,45,51). The major advantage of the IAG protocol would be its potential effectiveness without additional energy systems, control complexity, and high cost. ...
... Shulzhenko and Vil-Viliams (40,46) reported the beneficial effects of daily periodic exposures to ϩ0.8 to ϩ1.6 G z during 3 or 28 days of dry immersion in alleviating the G tolerance reduction. Vernikos et al. (43,44) reported that standing or walking for 2 or 4 h/day was effective in most cases to counteract the deconditioning effects of 4 days of Ϫ6°head-down bed rest. They concluded that various physiological systems benefit differently from daily short-duration ϩ1 G z gravitation; i.e., the preventive value appears to be system specific (43,44). ...
... Vernikos et al. (43,44) reported that standing or walking for 2 or 4 h/day was effective in most cases to counteract the deconditioning effects of 4 days of Ϫ6°head-down bed rest. They concluded that various physiological systems benefit differently from daily short-duration ϩ1 G z gravitation; i.e., the preventive value appears to be system specific (43,44). ...
... Signs of cardiovascular deconditioning can be observed after only a few days of HDBR; for example, Khan et al. (17) detected attenuated sympathetic nerve responses after 24 h of bed rest, whereas Johansen et al. (16) found a significant decrease of plasma volume (PV) after the same period. Several research groups have found impairments of OT and/or PV reductions after 4 days of bed rest (14,26,27,29). It was hypothesized therefore that a 5-day HDBR period would be suitable to test a novel AG protocol with respect to its ability to serve as a countermeasure against cardiovascular deconditioning. ...
... It was hypothesized that this intermittent protocol would not only be better tolerated but also prove more efficient as a countermeasure. This theory was based on the suggestion by Vernikos et al. (26) that not only the duration but also the number of gravity stimuli periods may be an important factor. ...
... Neither is the concept of using AG or normal gravity as countermeasures against cardiovascular decondition during actual and simulated microgravity. Thus Vernikos et al. (26) showed that standing for 2 or 4 h in 15-min bouts partially (2 h) or completely (4 h) prevented post-HDBR decreases of OT. Furthermore, Stenger et al. (25) showed clear improvements of OT in a controlled study, including two groups of subjects who were exposed to 21 days of HDBR with or without 60 min of daily AG. ...
Article
Exposure to artificial gravity (AG) in a short arm centrifuge has potential benefits for maintaining human performance during long-term space missions. Eleven subjects were investigated during three campaigns of five days head down bed rest: 1) bed rest without countermeasures (control), 2) bed rest and 30 min of AG (AG1) daily, and 3) bed rest and six periods of 5 min AG (AG2) daily. During centrifugation, the supine subjects were exposed to AG in the head-to-feet direction with 1 G at the center of mass. Subjects participated in the three campaigns in random order. The cardiovascular effects of bed rest and countermeasures were determined from changes in tolerance to a head-up tilt test with superimposed lower body negative pressure (HUT), from changes in plasma volume (PV) and from changes in maximum aerobic power (V̇O2peak) during upright work on a cycle ergometer. Complete data sets were obtained in eight subjects. After bed rest, HUT tolerance times were 36, 64, and 78% percent of pre-bed rest baseline during control, AG1 and AG2 respectively, with a significant difference between AG2 and control. Plasma volume and V̇O2peak decreased to 85 and 95% of pre-bed rest baseline, respectively, with no differences between the treatments. It was concluded that the AG2 countermeasure should be further investigated during future long term bed rest studies, especially as it was better tolerated than AG1. The superior effect of AG2 on orthostatic tolerance could not be related to concomitant changes in plasma volume or aerobic power.
... Physical exercise such as walking and running, can be utilized as effective countermeasures with definite compensatory effects on the cardiovascular and the musculoskeletal systems 7,8 . For bone, the magnitude and frequency of loading are important signals 9,10 , whereby 36 cycles of loading per day appear to be just as effective as 360 10 . ...
... Basic results on body mass, urine volume and hemodynamic changes to bed rest, as well as changes in plasma volume, exercise capacity and orthostatic tolerance with/without countermeasure are presented as part of the ESA standardized bed rest core data and given for standardized reference purposes. We hypothesized that the versatile upright exercise regime would counter the changes in the abovementioned parameters during 5 days of bed rest, and we based our hypothesis mainly on the work by Vernikos et al. 8 . These authors showed that two and four hours of daily standing or walking partly or completely prevented an otherwise severe impairment of orthostatic tolerance. ...
... The necessity to interrupt or prematurely cease the STA intervention in three subjects and the LRT intervention in two subjects due to presyncopal signs also supports this notion. Previously applied daily interventions such as active standing, passive centrifugation, or repeated exposure to lower body negative pressure have been shown to have protective effects against cardiovascular adaptation and orthostatic intolerance 8,22,[29][30][31] . Previously, Vernikos et al. 8 have shown that 4hr of upright walking/standing had a positive effect on orthostatic tolerance, but also that reduced orthostatic exposure had less of an effect. ...
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Objectives: This work provides a reference for future papers originating from this study by providing basic results on body mass, urine volume, and hemodynamic changes to 5 days of bed rest (BR) and by describing acute cardio-respiratory/mechanographic responses to a short versatile upright exercise battery. Methods: Ten male subjects (mean ± SEM age: 29.4 ± 1.5 years; height: 178.8 ± 1.5 cm; body mass: 77.7 ± 1.5 kg) performed, in random order, 5 days of 6° head-down tilt (HDT) BR with no exercise (CON), or BR with daily 25 minutes of quiet upright standing (STA) or upright locomotion replacement training (LRT). Results: Plasma volume, exercise capacity and orthostatic tolerance decreased similarly between interventions following 5 days of BR. Upright heart rate during LRT and STA increased throughout BR; from 137 ± 4 bpm to 146 ± 4 bpm for LRT (P<0.01); and from 90 ± 3 bpm to 102 ± 6 bpm (P<0.001) for STA. Conclusion: the overall similarity in the response to BR, and increase in upright heart rate during the LRT sessions suggest early and advancing cardiovascular deconditioning during 5 days of BR bed rest, which was not prevented by the versatile exercise regime.
... However, it is not yet known what the minimum requirements of G exposure would be for various physio-logical systems in order to prevent the deconditioning effects of microgravity. Vernikos and co-workers [34] have conducted a well designed human study to com- towards new set points, however, upon returning to Earth, these changes may lead to postflight orthostatic intolerance. Contrarily, bone loss is steadily increased and does not reach a new set point within 6 months (Source: https://asgsr.org/images/stories/slides/ ...
... The findings in animal studies on myocardial contractility and vascular remodeling support the results from several ground-based as well as spaceflight human studies, e.g., the Neurolab program, suggesting potential benefit of IAG in preventing postflight cardiovascular deconditioning and orthostatic intolerance [30,34] (for review, see [29] ). The findings on bone atrophy are consistent with the evidence of a steadily increased bone loss of astronauts. ...
... The findings on bone atrophy are consistent with the evidence of a steadily increased bone loss of astronauts. Our result supports that activity in +1 Gz is more effective than passive in alle-viating increased calcium excretion, suggesting the importance of muscle activity and impact loading in maintaining bone density [34] . Our results also support that the passive centrifugation will not be effective in maintaining bone integrity. ...
Article
It has been shown that the minimum gravity exposure requirements vary greatly among different physiological systems. A preliminary comparison between two extremes, vessels vs. bones, shows that not only the mechanostat at the tissue level differs greatly, but also the bone loss during weightlessness may also involve calcium deposition-resorption changes. It seems that the surprising efficacy of intermittent artificial gravity (IAG) is due to the vascular tissues possessing a strong resilience or "memory" function toward restoring their original pre-stress and tensegrity state at the 1 G environment. It appears that the bone tissue is related to a more complex tensegrity paradigm involving both osteoblasts and osteoclasts, and a longer half time for calcium deposition-absorption. Cell-level models (CellML) for calcium dynamics is currently available. We hope that the Physiome Project can use this modeling framework to help interpret the resistance of bones to IAG and to evaluate whether the "intermittent" or "continuous" AG scheme should be adopted eventually for future exploration-class spaceflight.
... Further loading is caused by impact forces and muscle activation from locomotion. Osteogenesis is commonly believed to be initiated when peak dynamic forces cause skeletal strains that exceed a threshold value [9,37]. However, static loading has been shown to protect bone as short periods of standing during bed rest can significantly reduce calcium excretion [37]. ...
... Osteogenesis is commonly believed to be initiated when peak dynamic forces cause skeletal strains that exceed a threshold value [9,37]. However, static loading has been shown to protect bone as short periods of standing during bed rest can significantly reduce calcium excretion [37]. Further, patients with spinal cord injuries lose considerable skeletal mass in the lower extremities, but maintain it in the lumbar spine due to gravitational loading in the wheel chair [9]. ...
Article
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Despite the use of several countermeasures, significant physiological deconditioning still occurs during long duration spaceflight. Bone loss – primarily due to the absence of loading in microgravity – is perhaps the greatest challenge to resolve. This paper describes a conceptual Gravity Loading Countermeasure Skinsuit (GLCS) that induces loading on the body to mimic standing and – when integrated with other countermeasures – exercising on Earth. Comfort, mobility and other operational issues were explored during a pilot study carried out in parabolic flight for prototype suits worn by three subjects. Compared to the 1- or 2-stage Russian Pingvin Suits, the elastic mesh of the GLCS can create a loading regime that gradually increases in hundreds of stages from the shoulders to the feet, thereby reproducing the weight-bearing regime normally imparted by gravity with much higher resolution. Modelling shows that the skinsuit requires less than 10 mmHg (1.3 kPa) of compression for three subjects of varied gender, height and mass. Negligible mobility restriction and excellent comfort properties were found during the parabolic flights, which suggests that crewmembers should be able to work normally, exercise or sleep while wearing the suit. The suit may also serve as a practical 1 g harness for exercise countermeasures and vibration applications to improve dynamic loading.
... The start time of the post-lunch study period is associated with a 3-hour accumulation of 9 sit-to-stand transitions in the 2-minute standing every 20 minutes condition, 6 minutes of walking in the 2-minute walking every hour condition, and 30 minutes of standing time in the 10-minute standing every hour condition (Fig 2). Head down bed rest studies also suggest that duration, condition-type, and accumulated number of standing or walking bout interruptions are moderators of physiological benefit [38]. Additional studies in a larger sample size are needed to further explore this observation and possible mechanisms. ...
... This pilot study suggests that different sitting interruption modalities will have different vascular and glucoregulatory outcomes. Similarly, head down bed rest studies demonstrate that standing and walking breaks can have differential benefits that vary by physiological outcome measure and that are more pronounced with accumulated exposures [38]. Feasibility, vascular, and suggestive glucoregulatory outcomes of this pilot study support the need for fully-powered, randomized controlled trials in this population. ...
Article
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Background Prolonged sitting is associated with cardiometabolic and vascular disease. Despite emerging evidence regarding the acute health benefits of interrupting prolonged sitting time, the effectiveness of different modalities in older adults (who sit the most) is unclear. Methods In preparation for a future randomized controlled trial, we enrolled 10 sedentary, overweight or obese, postmenopausal women (mean age 66 years ±9; mean body mass index 30.6 kg/m² ±4.2) in a 4-condition, 4-period crossover feasibility pilot study in San Diego to test 3 different sitting interruption modalities designed to improve glucoregulatory and vascular outcomes compared to a prolonged sitting control condition. The interruption modalities included: a) 2 minutes standing every 20 minutes; b) 2 minutes walking every hour; and c) 10 minutes standing every hour. During each 5-hr condition, participants consumed two identical, standardized meals. Blood samples, blood pressure, and heart rate were collected every 30 minutes. Endothelial function of the superficial femoral artery was measured at baseline and end of each 5-hr condition using flow-mediated dilation (FMD). Participants completed each condition on separate days, in randomized order. This feasibility pilot study was not powered to detect statistically significant differences in the various outcomes, however, analytic methods (mixed models) were used to test statistical significance within the small sample size. Results Nine participants completed all 4 study visits, one participant completed 3 study visits and then was lost to follow up. Net incremental area under the curve (iAUC) values for postprandial plasma glucose and insulin during the 5-hr sitting interruption conditions were not significantly different compared to the control condition. Exploratory analyses revealed that the 2-minute standing every 20 minutes and the 2-minute walking every hour conditions were associated with a significantly lower glycemic response to the second meal compared to the first meal (i.e., condition-matched 2-hour post-lunch glucose iAUC was lower than 2-hour post-breakfast glucose iAUC) that withstood Bonferroni correction (p = 0.0024 and p = 0.0084, respectively). Using allometrically scaled data, the 10-minute standing every hour condition resulted in an improved FMD response, which was significantly greater than the control condition after Bonferroni correction (p = 0.0033). Conclusion This study suggests that brief interruptions in prolonged sitting time have modality-specific glucoregulatory and vascular benefits and are feasible in an older adult population. Larger laboratory and real-world intervention studies of pragmatic and effective methods to change sitting habits are needed. Trial registration ClinicalTrials.gov NCT02743286.
... The AG training effects on either humans or animals are equivalent to those of natural gravity. It functions by exerting a centrifugal force on a body accelerated centripetally in a rotating device (15)(16)(17). The participant lies in a supine and horizontal position on the rotation bed with the head toward the center. ...
... EEG analysis was performed for each epoch separately. It extracted the relative energy contribution of each EEG rhythm: delta (0.5-4 Hz), theta (4-8 Hz), alpha (8)(9)(10)(11)(12), beta (12)(13)(14)(15)(16)(17)(18)(19)(20) and gamma at both the sensor and cortical levels. It was based on the orthogonal discrete wavelet transform, as described in Frantzidis et al. (22). ...
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Short-arm human centrifugation (SAHC) is proposed as a robust countermeasure to treat deconditioning and prevent progressive disability in a case of secondary progressive multiple sclerosis. Based on long-term physiological knowledge derived from space medicine and missions, artificial gravity training seems to be a promising physical rehabilitation approach toward the prevention of musculoskeletal decrement due to confinement and inactivity. So, the present study proposes a novel infrastructure based on SAHC to investigate the hypothesis that artificial gravity ameliorates the degree of disability. The patient was submitted to a 4-week training programme including three weekly sessions of 30 min of intermittent centrifugation at 1.5–2 g . During sessions, cardiovascular, muscle oxygen saturation (SmO 2 ) and electroencephalographic (EEG) responses were monitored, whereas neurological and physical performance tests were carried out before and after the intervention. Cardiovascular parameters improved in a way reminiscent of adaptations to aerobic exercise. SmO 2 decreased during sessions concomitant with increased g load, and, as training progressed, SmO 2 of the suffering limb dropped, both effects suggesting increased oxygen use, similar to that seen during hard exercise. EEG showed increased slow and decreased fast brain waves, with brain reorganization/plasticity evidenced through functional connectivity alterations. Multiple-sclerosis-related disability and balance capacity also improved. Overall, this study provides novel evidence supporting SAHC as a promising therapeutic strategy in multiple sclerosis, based on mechanical loading, thereby setting the basis for future randomized controlled trials.
... These reductions may compromise crew members' ability to perform mission-critical activities, such as extravehicular activities (spacewalks) and postflight emergency egress [McCrory, 2002], and prolong the return to activities of daily living after landing. Further, altered locomotion and neuromuscular activation patterns following space flight may impair the ability of space travelers to ambulate [Edgerton, 2000;Layne, 1997;Vernikos, 1996] during extraterrestrial activities (such as on Mars or Earth's moon), emergency egress, or normal activities upon return to Earth. Although lacking the orthostatic stress of upright exercise in normal gravity (1g), it is believed that treadmill exercise during microgravity (0g) protects exercise and metabolic capacities, simulates 1g loads to the musculoskeletal system, and stimulates neuromuscular patterns required for locomotion [Convertino, 1996;Watenpaugh, 2000]. ...
... The benefit of exercise countermeasures over other interventions, such as pharmacological agents, is that muscular activity is affected by or affects virtually every system in the body and, therefore, should be a potent countermeasure. NASA's goal is to develop a countermeasure prescription that stimulates or maintains the adaptations to the normal 1g environment through the efficient manipulation of a variety of physiologic systems [Vernikos, 1996] in a minimal amount of time. ...
... In a pioneering study, Vernikos et al. 6 demonstrated that intermittent (real) gravity loading can effectively reduce the deconditioning associated with prolonged bed rest in healthy human males. She showed that intermittent standing or controlled walking during otherwise continuous bed rest prevented post-bed rest orthostatic intolerance and attenuated decrements in peak oxygen uptake, plasma volume, and urinary Ca ++ excretion. ...
... The outcome of which was a book 21 and a detailed set of recommendations for undertaking a program of ground-based research into the feasibility of using intermittent gravity loading plus supplemental exercise as a multi-system countermeasure. The first step of this program was very short-duration (5 days) bed rest studies to establish the effective ranges of intermittent gravity loading on sensorymotor, cardiovascular, and musculoskeletal systems, using either real gravity such as Vernikos et al. 6 or short-radius centrifugation. These studies used a crossover design that required all subjects to experience each test condition. ...
Article
Objectives: We tested whether intermittent standing or a combination of heel raising, squatting and hopping exercises was sufficient to prevent alteration in balance and gait following a 5-day bed rest. Methods: This cross-over design study was performed with 10 male subjects during 6° head down tilt: (a) with no countermeasure; (b) while standing 25 min per day; (c) during locomotion-like activities 25 min per day. Gait was evaluated by grading subjects' performance during various locomotion tasks. Equilibrium scores were derived from peak-to-peak anterior-posterior sway while standing on a foam pad with the eyes open or closed or while making pitch head movements. Results: When no countermeasure was used, head movements led to decreased postural stability and increased incidence of falls immediately after bed rest compared to before. When upright standing or locomotion-like exercises were used, postural stability and the incidence of falls were not significantly different after the bed rest from the baseline. Conclusion: These results indicate that daily 25-min of standing or locomotion-like exercise proves useful against postural instability following a 5-day bed rest. The efficacy of these countermeasures on locomotion could not be evaluated, however, because gait was not found to be altered after a 5-day bed rest.
... Moreover, all DI experiments performed until now included a short daily raise for personal hygiene procedures and weighing (Navasiolava et al., 2011a). Importantly, literature shows that this type of short daily orthostatic stimulation could act as a countermeasure (Greenleaf, 1984;Vernikos et al., 1996). Therefore, in order to eliminate this aberration, our novel DI protocol did not permit subjects to rise at all for 3 days, and a −6 • head down position was maintained when the subjects were out of water, as is observed in strict bedrest protocols. ...
... Periodic short gravitational stimuli appear to be effective countermeasures, maintaining gravitational tolerance. Vernikos et al. (1996) demonstrated a very efficient preventive effect of a short period in a standing position (for 2 h daily) against orthostatic intolerance after 4 days of HDBR. The beneficial effect of LBNP for 20 min/day during both spaceflight and bed rest was discussed in a review by Clement and Pavy-Le Traon (2004). ...
Article
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Dry immersion (DI) is a Russian-developed, ground-based model to study the physiological effects of microgravity. It accurately reproduces environmental conditions of weightlessness, such as enhanced physical inactivity, suppression of hydrostatic pressure and supportlessness. We aimed to study the integrative physiological responses to a 3-day strict DI protocol in 12 healthy men, and to assess the extent of multi-system deconditioning. We recorded general clinical data, biological data and evaluated body fluid changes. Cardiovascular deconditioning was evaluated using orthostatic tolerance tests (Lower Body Negative Pressure + tilt and progressive tilt). Metabolic state was tested with oral glucose tolerance test. Muscular deconditioning was assessed via muscle tone measurement. Results: Orthostatic tolerance time dropped from 27 ± 1 to 9 ± 2 min after DI. Significant impairment in glucose tolerance was observed. Net insulin response increased by 72 ± 23% on the third day of DI compared to baseline. Global leg muscle tone was approximately 10% reduced under immersion. Day-night changes in temperature, heart rate and blood pressure were preserved on the third day of DI. Day-night variations of urinary K+ diminished, beginning at the second day of immersion, while 24-h K+ excretion remained stable throughout. Urinary cortisol and melatonin metabolite increased with DI, although within normal limits. A positive correlation was observed between lumbar pain intensity, estimated on the second day of DI, and mean 24-h urinary cortisol under DI. In conclusion, DI represents an accurate and rapid model of gravitational deconditioning. The extent of glucose tolerance impairment may be linked to constant enhanced muscle inactivity. Muscle tone reduction may reflect the reaction of postural muscles to withdrawal of support. Relatively modest increases in cortisol suggest that DI induces a moderate stress effect. In prospect, this advanced ground-based model is extremely suited to test countermeasures for microgravity-induced deconditioning and physical inactivity-related pathologies.
... Gravity as an effective countermeasure to bed restinduced cardiovascular deconditioning was established many years ago in a study demonstrating that exposure to Earth's gravity (2 h of standing each day) improved orthostatic tolerance in bed-rested men (Vernikos et al. 1996). However, since gravity is absent during space missions, we previously conducted a series of studies using exposure to short radius AG (centrifugation) in a long-term "training" model to explore its efficacy as a countermeasure to deconditioning (Evans et al. 2004;Stenger et al. 2007;Stenger et al. 2012). ...
... Day × gender: males on AG day < males on HDBR day (p < 0.04) and males > females on HDBR day (p < 0.04), time point × gender: males > females at recovery, p < 0.03 normovolemic men and women (Goswami et al. 2013;Goswami et al. 2015). The hypothesis for both studies was based on results from previous studies we, and others, conducted in which it was established that artificial gravity training or standing in earth gravity improved orthostatic tolerances of ambulatory men and women (Evans et al. 2004;Stenger et al. 2007), and of deconditioned (bed rest) men (Stenger et al. 2012;Vernikos et al. 1996). A major difference between the present (and its companion) study and previous studies was the fact that the current studies demonstrate effects of a single bout of AG exposure on subsequent orthostatic tolerance. ...
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Purpose: In addition to serious bone, vestibular, and muscle deterioration, space flight leads to cardiovascular dysfunction upon return to gravity. In seeking a countermeasure to space flight-induced orthostatic intolerance, we previ ously determined that exposure to artificial gravity (AG) training in a centrifuge improved orthostatic tolerance of ambulatory subjects. This protocol was more effective in men than women and more effective when subjects exercised. Methods: We now determine the orthostatic tolerance limit (OTL) of cardiovascularly deconditioned (furosemide) men and women on one day following 90 min of AG compared to a control day (90 min of head-down bed rest, HDBR). Results: There were three major findings: a short bout of artificial gravity improved orthostatic tolerance of hypovolemic men (30 %) and women (22 %). Men and women demonstrated different mechanisms of cardiovascular regulation on AG and HDBR days; women maintained systolic blood pressure the same after HDBR and AG exposure while men's systolic pressure dropped (11 ± 2.9 mmHg) after AG. Third, as presyncopal symptoms developed, men's and women's cardiac output and stroke volume dropped to the same level on both days, even though the OTL test lasted significantly longer on the AG day, indicating cardiac filling as a likely variable to trigger presyncope. Conclusions: (1) Even with gender differences, AG should be considered as a space flight countermeasure to be applied to astronauts before reentry into gravity, (2) men and women regulate blood pressure during an orthostatic stress differently following exposure to artificial gravity and (3) the trigger for presyncope may be cardiac filling.
... The rationale for this theory stems from studies on hind-limb suspension in rats 17 and in-orbit exercises in astronauts 18 , which showed that repetitive short-duration, high-load exercise training was the most effective and efficient means of reducing physiological deconditioning. Vernikos et al. 19 also suggested that the frequency of gravity exposure rather than the duration was a critical factor for mitigating physiological deconditioning due to unloading. ...
... The intermittent centrifugation protocol generated six of these virtual head-up tilts each day of the bed rest, compared to only one per day for the continuous centrifugation protocol. The repetition of this cardiovascular stress test presumably prepared the cardiovascular system for the actual head-up tilt at the end of the bed rest after intermittent centrifugation 19 . Also, the repetitive character of intermittent centrifugation is more likely to induce a habituation of endocrine stress response. ...
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Objectives: We tested whether intermittent short-radius centrifugation was effective for mitigating alteration in balance and gait following bed rest. Methods: Ten male subjects were exposed to 5 days of 6° head-down tilt bed rest with: (a) no countermeasure; (b) daily 1-g centrifugation for a continuous 30-min period; and (c) daily 1-g centrifugation for six periods of 5 min. During and after the bed rest, subjects were asked to scale the severity of neurovestibular symptoms that followed centrifugation or 80° head-up tilt. Following the bed rest, equilibrium scores were derived from anterior-posterior sway while standing on a foam pad with the eyes open or closed while making pitch head movements, and gait was evaluated by grading subjects' performance during various locomotion tasks. Results: At the beginning of bed rest, one single 30-min period of centrifugation induced more severe neurovestibular symptoms than six periods of 5-min centrifugation. After bed rest, although equilibrium scores and gait performance were not significantly altered, subjects felt less neurovestibular dysfunction with orthostatic stress when centrifugation was used. Conclusion: Centrifugation was effective at reducing the severity of neurovestibular symptoms after bed rest, but this decrease was not different between one or multiple daily sessions.
... Artificial gravity (AG) as a countermeasure to physiologic deconditioning of multiple organ systems has long been discussed and proposed (National Research Council, 2011, Chapter 7 of Recapturing a Future for Space Exploration; Shulzhenko, 1992;Vernikos et al., 1996;Vernikos, 1997;Greenleaf et al., 1998;Clement and Pavy-Le Traon, 2004;Evans et al., 2004Evans et al., , 2015Clement et al., 2016). To date, however, cardiovascular responses to AG applied in the long body axis (to simulate standing on Earth) have come almost exclusively from Earth-based studies in a variety of situations: (1) healthy, ambulatory subjects acutely exposed to hypergravity, (2) healthy, ambulatory subjects before and after a period of AG training, and (3) deconditioned subjects before and after bed rest, HDBR, water immersion, dry immersion, and furosemide-induced simulations of spaceflight. ...
... White et al. (1966) used 1.75 Gz (heart level) applied in four, 20 min daily sessions, to prevent the development of OI in men during 10 days of bed rest. Pavy-Le Traon et al.'s (2007) review of 20 years of bed rest studies, included studies in which gravity was used as a countermeasure; it was apparent from early days, that as little as standing 2 h a day would lessen the incidence of OI in men bed rested for 4 days (Vernikos et al., 1996). Iwasaki et al. (2001) study determined that two, 30 min bouts of 2 Gz applied daily, could prevent the development of OI as well as shifts in autonomic balance toward sympathetic dominance during 4 days of HDBR. ...
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Space flight-induced physiological deconditioning resulting from decreased gravitational input, decreased plasma volume, and disruption of regulatory mechanisms is a significant problem in returning astronauts as well as in normal aging. Here we review effects of a promising countermeasure on cardiovascular systems of healthy men and women undergoing Earth-based models of space-flight. This countermeasure is produced by a centrifuge and called artificial gravity (AG). Numerous studies have determined that AG improves orthostatic tolerance (as assessed by various protocols) of healthy ambulatory men, of men deconditioned by bed rest or by immersion (both wet and dry) and, in one case, following spaceflight. Although a few studies of healthy, ambulatory women and one study of women deconditioned by furosemide, have reported improvement of orthostatic tolerance following exposure to AG, studies of bed-rested women exposed to AG have not been conducted. However, in ambulatory, normovolemic subjects, AG training was more effective in men than women and more effective in subjects who exercised during AG than in those who passively rode the centrifuge. Acute exposure to an AG protocol, individualized to provide a common stimulus to each person, also improved orthostatic tolerance of normovolemic men and women and of furosemide-deconditioned men and women. Again, men’s tolerance was more improved than women’s. In both men and women, exposure to AG increased stroke volume, so greater improvement in men vs. women was due in part to their different vascular responses to AG. Following AG exposure, resting blood pressure (via decreased vascular resistance) decreased in men but not women, indicating an increase in men’s vascular reserve. Finally, in addition to counteracting space flight deconditioning, improved orthostatic tolerance through AG-induced improvement of stroke volume could benefit aging men and women on Earth.
... Concomitantly, neuromuscular control of the skeletal muscle with an emphasis on antagonistic coordination could be preserved throughout the high-intensity jump exercise performed during bed-rest. Other bed-rest studies validating countermeasures such as strength training (Haines, 1974;Kouzaki et al., 2007), flywheel (Viguier et al., 2009), and treadmill (Macaulay et al., 2016), lower-body negative-pressure (Dupui et al., 1992), mechanical stimulation (Muir et al., 2011) or centrifugation (Vernikos et al., 1996), found plyometric jump training to be advantageous compared to past alternatives. Despite differing HDT periods ranging from 5 days to 12 weeks, none of these countermeasures succeeded in entirely preserving gait, posture and functional mobility during bed-rest (Haines, 1974;Dupui et al., 1992;Vernikos et al., 1996;Kouzaki et al., 2007;Macaulay et al., 2016) despite those that permitted daily upright stance, and used standing and walking as exercise modes (Mulder et al., 2014). ...
... Other bed-rest studies validating countermeasures such as strength training (Haines, 1974;Kouzaki et al., 2007), flywheel (Viguier et al., 2009), and treadmill (Macaulay et al., 2016), lower-body negative-pressure (Dupui et al., 1992), mechanical stimulation (Muir et al., 2011) or centrifugation (Vernikos et al., 1996), found plyometric jump training to be advantageous compared to past alternatives. Despite differing HDT periods ranging from 5 days to 12 weeks, none of these countermeasures succeeded in entirely preserving gait, posture and functional mobility during bed-rest (Haines, 1974;Dupui et al., 1992;Vernikos et al., 1996;Kouzaki et al., 2007;Macaulay et al., 2016) despite those that permitted daily upright stance, and used standing and walking as exercise modes (Mulder et al., 2014). ...
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Physical inactivity causes a deconditioning of the human body. Concerns due to chronic bed-rest include deficits in posture and gait control, predisposing individuals to an increased fall and injury risk. This study assessed the efficiency of a high-load jump exercise (JUMP) as a countermeasure to prevent detrimental effects on gait, posture control and functional mobility. In an RCT (23 males), the effect of 60 days bed-rest without training was compared to JUMP. JUMP is characterized by plyometric executed as a high intensity interval training. Typical trainings session consisted of 4 × 10 countermovement jumps and 2 × 10 hops in a sledge jump system. We assessed sway path and muscle activity in monopedal stance, spatiotemporal, kinematic, and variability characteristics in gait, functional mobility with repeated chair-rises and Timed Up and Go (TUG). Results revealed: The JUMP group showed no significant changes after bed-rest, whereas the control group exhibited substantial deteriorations: an increased sway path (+104%, p < 0.05) was accompanied by increased co-contractions of antagonistic muscles encompassing the ankle (+32%, p < 0.05) and knee joint (45%, p < 0.05). A reduced locomotor speed (−22%, p < 0.05) was found concomitant with pathological gait rhythmicity (p < 0.05), reduced joint excursions (ankle −8%, knee −29%, p < 0.05) and an increased gait variability (p < 0.05). Chair-rising was slowed (+28%, p < 0.05) with reduced peak power (+18%, p < 0.05), and more time was needed to accomplish TUG (+39%, p < 0.05). The effects persisted for a period of 1 month after bed-rest. Increases in sway path were correlated to decreases in gait speed. The JUMP effectively preserved the neuromuscular system's ability to safely control postural equilibrium and perform complex locomotor movements, including fast bipedal gait with turns and rises. We therefore recommend JUMP as an appropriate strategy combatting functional deconditioning.
... While these health benefi ts from exercise are important, the type of movement that is being lost in our modern-day lifestyles, that may be even more important to our health is daily general, Non-Exercise Physical Activity (NEPA), which includes interacting with/changing positions relative to gravity [1][2][3][4][5]. ...
... These conditions are all linked to decreased physical activity. health indicate that it is intermittent, vertical alternating movement throughout the day-every 30 to 60minutes-that is most benefi cial [1][2][3][4][5], rather than the total hours sat. ...
... Cleary, a period of continuous 6-8 hours per day of Gx stimulation is sufficient to protect from deconditioning. During continuous bed rest, Vernikos and colleagues at NASA Ames have showed the potential protection afforded by 2-4 hours of daily standing or walking (Gz) in preventing orthostatic intolerance, plasma loss or calcium loss, but not in maintaining aerobic capability (Vernikos et al. 1996). Bed rest therefore offers the possibility to investigate the minimum gravity load needed along Gx and Gz axis as a countermeasure for some of the effects seen in space. ...
... Studies have shown that in as little as 4-5 days, plasma volume and aerobic conditioning are significantly decreased, orthostatic intolerance is evident calcium excretion and bone loss markers are increased (Vernikos et al. 1996). Based on these parameters, 5-day bed rest studies should suffice for the rapid screening of countermeasures such as centrifugation, to narrow down intensity, duration and frequency variables. ...
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In this final chapter, we address the next steps in artificial gravity research, both short- and long-term, required to understand the fundamentals and validate the operational aspects of using artificial gravity as an effective countermeasure for long-duration space travel. Our recommendations are based on both the summaries presented in the preceding chapters as well as
... The factors (i.e., G levels, exposure duration, and frequency) that might provoke an increase in tolerance to a hypergravity environment remain largely unknown. Changes in orthostatic tolerance associated with decreased hydrostatic pressure (e.g., recumbency, microgravity) require chronic exposure lasting days to months, and even temporary restoration of a gravitational stress, either through standing ( 20 ), lower-body negative pressure exercise ( 21 ), or artifi cial gravity ( 19 ) corrects the defi cit. These environments are also associated with changes in transmural pressure, which alter the function and structure of peripheral blood vessels ( 25 ), and an increase in pressure distension in dependent vessels ( 3 ). ...
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Repeated exposure to +Gz acceleration provokes cardiovascular adaptations of potential benefit to pilots' +Gz tolerance, but whether such changes actually improve human tolerance to +Gz acceleration is uncertain. This study assessed +Gz tolerance before and after repeated exposure to +Gz at two different intensities as the role of frequency of +Gz exposure in adaptation also remains unknown. In a cross-over design, 10 experienced male centrifuge volunteers completed two experimental conditions separated by at least 3 wk. Subjects completed four simulated air combat maneuvers (SACM) on a human centrifuge, either twice or four times per week, for 3 consecutive weeks. Relaxed +Gz tolerance (RGT) during a gradual onset run (GOR, 0.1 G x s(-1)) and cardiovascular responses to rapid and incremental head-up tilt were assessed before and after each condition. Rapid and incremental head-up tilt increased both mean arterial and diastolic blood pressures following +Gz exposure. +Gz exposure attenuated the increase in heart rate (+9 +/- 3 vs. +11 +/- 3 mmHg/Gz) and the decrease in eye-level systolic blood pressure (-11 +/- 3 vs. -14 +/- 4 mmHg/Gz) during GOR, but had no effect on RGT (4/wk: +3.88 +/- 0.56 vs. +3.92 +/- 0.63 Gz; 2/wk: +3.89 +/- 0.69 vs. +3.92 +/- 0.69 Gz). Frequent +Gz acceleration, either as 2 (8 SACMs) or 4 sessions (16 SACMs) per week for 3 wk, enhances cardiovascular tolerance to orthostatic stress but does not improve RGT measured during a GOR.
... AG also reintroduces hydrostatic gradients in the body and causes a fluid shift toward the lower extremities. Aside from being greatly beneficial to the cardiovascular system [4,5], hydrostatic gradients also cause an increase in blood flow to muscles of the lower body [6]. In addition, the fluid shift is potentially important to bone remodeling. ...
Article
The current, system-specific countermeasures to space deconditioning have limited success with the musculoskeletal system in long duration missions. Artificial gravity (AG) that is produced by short radius centrifugation has been hypothesized as an effective countermeasure because it reintroduces an acceleration field in space; however, AG alone might not be enough stimuli to preserve the musculoskeletal system. A novel combination of AG coupled with one-legged squats on a vibrating platform may preserve muscle and bone in the lower limbs to a greater extent than the current exercise paradigm. The benefits of the proposed countermeasure have been analyzed through the development of a simulation platform. Ground reaction force data and motion data were collected using a motion capture system while performing one-legged and two-legged squats in 1-G. The motion was modeled in OpenSim, an open-source software, and inverse dynamics were applied in order to determine the muscle and reaction forces of lower limb joints. Vibration stimulus was modeled by adding a 20Hz sinusoidal force of 0.5 body weight to the force plate data. From the numerical model in a 1-G acceleration field, muscle forces for quadriceps femoris, plantar flexors and glutei increased substantially for one-legged squats with vibration compared to one- or two-legged squats without vibration. Additionally, joint reaction forces for one-legged squats with vibration also increased significantly compared to two-legged squats with or without vibration. Higher muscle forces and joint reaction forces might help to stimulate muscle activation and bone modeling and thus might reduce musculoskeletal deconditioning. These results indicate that the proposed countermeasure might surpass the performance of the current space countermeasures and should be further studied as a method of mitigating musculoskeletal deconditioning.
... They conclude that various physiological systems benefit differentially from passive gravity/activity in one g. Moreover, in addition to the duration of the stimulus, the number of exposures to upright posture are important as well (Vernikos et al., 1996). ...
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This paper reviews our experience with 30-day head-down tilt (HDT) bed rest studies of supine lower body negative pressure (LBNP) treadmill exercise countermeasure in identical twins. We review our experience with 16 sets of identical male and females twins in order to improve future countermeasure studies for long-duration space flight. All male sets of twins and all but one female set tolerated the study well and no medical complications occurred. Our experimental design and use of identical twins may represent an innovative method for evaluating the physiologic efficacy of a treatment when comparing an exercise versus control group. Also, our nutritional procedures maintained body weight in both groups. Pre-and post-bed rest tests were scheduled to avoid confounding effects due to test order and test volume. As reported elsewhere, our treadmill exercise protocol within LBNP maintained plasma volume, orthostatic responses, upright exercise capacity, muscle strength and endurance during bed rest. Future bed rest studies should focus on the recruitment of healthy, non-sedentary subjects and may want to follow our recommendations in terms of screening, testing sequence, nutrition, medical care and subject support. Identical twins offer unique insights into countermeasure development and heritability of physiologic traits.
... The cause of the impairment of vascular function on returning to Earth's 1-G environment is apparently related to the adaptation of resistance vessels to altered wall stress due to loss of hydrostatic pressure gradients during microgravity exposure [3,7,8] . Therefore, gravity-based countermeasures like intermittent artificial gravity (IAG) by incorporating a short-arm centrifuge into the spacecraft, or exercise within lower body negative pressure (LBNP), have been suggested for future spaceflight [3,5,7,[9][10][11][12] . ...
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The aim of the present study was to evaluate the active and passive mechanical properties and wall collagen and elastin contents of mesenteric small arteries (MSAs) isolated from rats of 28-day simulated microgravity (SUS), countermeasure [S + D: SUS plus 1 h/d -G(x) to simulate intermittent artificial gravity (IAG)] and control (CON) groups. Three mechanical parameters were calculated: the overall stiffness (β), circumferential stress (σ(θ))-strain (ε(θ)) relationship and pressure-dependent incremental elastic modulus (E(inc,p)). Vessel wall collagen and elastin percentage were quantified by electron microscopy. The results demonstrate that the active mechanical behavior of MSAs differs noticeably among the three groups: the active stress-strain curve of SUS vessels is very close to the passive curve, whereas the active σ(θ)-ε(θ) curves of CON and S + D vessels are shifted leftward and display a parabolic shape, indicating that for MSAs isolated from S + D, but not those from SUS rats, the pressure-induced myogenic constriction can effectively stiffen the vessel wall as the CON vessels. The passive mechanical behavior of MSAs does not show significant differences among the three groups. However, the percentage of collagen is decreased in the wall of SUS and S + D compared with CON vessels in the following order: SUS < S + D < CON. Thus, the relationship between passive mechanical behavior and compositional changes may be complex and yet depends on factors other than the quantity of collagen and elastin. These findings have provided biomechanical data for the understanding of the mechanism of postflight orthostatic intolerance and its gravity-based countermeasure.
... Si l"on opte pour un levé quotidien de 15 minutes (ce qui est fait habituellement), il faudra nécessairement en comparer les résultats avec ceux des expériences d"alitement comprenant également un levé quotidien. Une brève stimulation orthostatique quotidienne peut jouer le rôle de contremesure ( Greenleaf 1984, Vernikos et al. 1996). Si l"on veut maintenir le protocole « strict », il faut minimiser les périodes hors baignoire (douche, pesée) et au mieux, maintenir la position horizontale pendant ces périodes. ...
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The indirect estimation of lipopolysaccharide (LPS) translocation by measuring of IL-6 serum level after LPS injection was carried out. We found a decreased response to LPS injection as the result of previous LPS translocation in rats after the repeated injection of LPS in 7 days after the first injection. Under electron microscopy, fringle-looking protrusions in vessel lumen, disturbance of basal membrane integrity and infringement of interendothelial junctions, adhesion of leucocytes were found in arterioles of these groups of animals. So, we suppose that translocation of LPS from gut could occur in simulated weightlessness model in rats (HDT) and could be associated with endothelial dysfunction.
... Prolonged bed-rest has been associated with decreases in cardiovascular and muscular performance with reduced physical work capacity [1][2][3][4][5][6][7]. An active individual who is suddenly restricted from daily activities may, therefore, experience several physiological side-effects related to bed-rest (or activity restriction). ...
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Considering the maternal risk for both short- and long-term disability imposed by activity restriction, it is of great concern that the antepartum symptoms of bed rest are still evident in the postpartum period. The benefits of bed-rest-exercise may alleviate or even prevent physiological distresses or deconditioning associated with activity restriction, thus, eliminating or stabilizing, factors that may augment existing complications. This is the first study to investigate the feasibility of incorporating a bed-rest exercise program in a specific hospitalized twin pregnancy case. The maternal physiological responses of heart rate, blood pressure and uterine contractions to a four week bed-rest resistance program were measured in a woman hospitalized due to complications during her twin pregnancy. A second participant (same diagnoses) was included as a control. The bed-rest-exercise reduced the degree of swelling in the lower extremities, promoted more energy during the day and a better night’s sleep. There were no significant differences in uterine contractions pre vs. post protocol and all babies were born healthy.
... Interstitial volume is however preserved. 5 Decrease in ADH secretion with a resultant 4% decrease in plasma osmolarity. Serum sodium decreases by 6% which stimulates aldosterone secretion. ...
... White et al. [31] used 4 daily AG sessions of 7.5 min or 11.2 min during bed rest and showed that this was sufficient to reduce most of the physiological markers associated with orthostatic intolerance. Vernikos et al. [24] used 8-16 daily sessions where the subjects were standing in place or walking during 4-day bed rest, based on the concept that ''in general physiological systems respond to signal and intensity changes rather than to the duration of a stimulus" [55]. Recent studies have shown positive effects of AG for a total exposure equal to less than 1% the intervention [30]. ...
... As such, artificial gravity (AG) has been proposed in the form of human centrifugation for ~ 20 years (Kreitenberg et al. 1998), which has been employed as a countermeasure during short-duration (5 days) HDBR (Rittweger et al. 2015). It was shown that short bouts of intermittent AG with the same duration of AG exposure in one single bout were better tolerated (Vernikos et al. 1996) and improved isometric strength of the knee extensors and flexors (Rittweger et al. 2015). Therefore, AG may be a promising countermeasure to maintain the neuromuscular system during long-term microgravity and HDBR-induced disuse. ...
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PurposeThe objective of this study was to assess whether artificial gravity attenuates any long-duration head-down 60 bed rest (HDBR)-induced alterations in motor unit (MU) properties.Methods Twenty-four healthy participants (16 men; 8 women; 26–54 years) underwent 60-day HDBR with (n = 16) or without (n = 8) 30 min artificial gravity daily induced by whole-body centrifugation. Compound muscle action potential (CMAP), MU number (MUNIX) and MU size (MUSIX) were estimated using the method of Motor Unit Number Index in the Abductor digiti minimi and tibialis anterior muscles 5 days before (BDC-5), and during day 4 (HDT4) and 59 (HDT59) of HDBR.ResultsThe CMAP, MUNIX, and MUSIX at baseline did not change significantly in either muscle, irrespective of the intervention (p > 0.05). Across groups, there were no significant differences in any variable during HDBR, compared to BDC-5.Conclusion Sixty days of HDBR with or without artificial gravity does not induce alterations in motor unit number and size in the ADM or TA muscles in healthy individuals.
... However, in our present study we find that a constant artificial gravity is caused less vestibular stimulation and could be accepted easily by ordinary individuals (the data is to be published in the future). Results from previous HDBR studies were inconsistent regarding AG alone as a countermeasure for decreased VO 2max countermeasures, such as quiet standing (Vernikos et al. 1996) and use of a reverse pressure gradient garment (Convertino et al. 1982b), provided full or partial protection against the decline in VO 2max in some HDBR studies. ...
Article
Numerous countermeasures have been proposed to minimize microgravity-induced physical deconditioning, but their benefits are limited. The present study aimed to investigate whether personalized aerobic exercise based on artificial gravity (AG) mitigates multisystem physical deconditioning. Fourteen men were assigned to the control group (n=6) and the countermeasure group (CM, n=8). Subjects in the CM group were exposed to AG (2Gz at foot level) for 30 min twice daily, during which time cycling exercise of 80-95% anaerobic threshold (AT) intensity was undertaken. Orthostatic tolerance (OT), exercise tests, and blood assays were determined before and after 4 days head-down bed rest (HDBR). Cardiac systolic function was measured every day. After HDBR, OT decreased to 50.9% and 77.5% of pre-HDBR values in control and CM groups, respectively. Exercise endurance, maximal oxygen consumption, and AT decreased to 96.5%, 91.5% and 91.8% of pre-HDBR values, respectively, in the control group. Nevertheless, there were slight changes in the CM group. HDBR increased heart rate, sympathetic activity, and the pre-ejection period, but decreased plasma volume, parasympathetic activity and left-ventricular ejection time in the control group, whereas these effects were eliminated in the CM group. Aldosterone had no change in the control group but increased significantly in the CM group. Our study shows that 80-95% AT aerobic exercise based on 2Gz of AG preserves OT and exercise endurance, and affects body fluid regulation during short-term HDBR. The underlying mechanisms might involve maintained cardiac systolic function, preserved plasma volume, and improved sympathetic responses to orthostatic stress.
... Evidence derived from controlled trials in laboratory settings with young to middle-aged adults has established that early activity, in the form of returning persons to their usual upright activity level, is the most efficient and effective non-invasive way to prevent and rehabilitate orthostatic intolerance [24][25][26][27][28][29]. Early activity in the hospital setting delivered during the acute phase of an illness has been minimally evaluated as a single component intervention and its effect on orthostatic intolerance has not been examined in older patients with multiple chronic conditions admitted to medical units. ...
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Background Hospitalized older patients spend most of their time in bed, putting them at risk of experiencing orthostatic intolerance. Returning persons to their usual upright activity level is the most effective way to prevent orthostatic intolerance but some older patients have limited activity tolerance, supporting the need for low-intensity activity interventions. Consistent with current emphasis on patient engagement in intervention design and evaluation, this study explored older hospitalized patients’ perceived acceptability of, and preference for, two low-intensity early activity interventions (bed-to-sitting and sitting-to-walking), and characteristics (gender, illness severity, comorbidity, illnesses and medications with orthostatic effects, and baseline functional capacity) associated with perceived acceptability and preference. MethodsA convenience sample was recruited from in-patient medical units of two hospitals in Ontario, Canada and included 60 cognitively intact adults aged 65+ who were admitted for a medical condition within the past 72 h, spent ≥ 24 consecutive hours on a stretcher or in bed, presented with ≥ 2 chronic diseases, understood English, and were able to ambulate before admission. A cross-sectional observational design was used. Participants were presented written and oral descriptions and a 2-min video of each intervention. The sequence of the interventions’ presention was randomized. Following the presentation, a research nurse administered measures of perceived acceptability and preference, and collected health and demographic data. Perceived acceptability and preference for the interventions were measured using the Treatment Acceptability and Preferences Scale. Illness severity was measured using the Modified Early Warning Score. Comorbidity was assessed with the Age Adjusted Charlson Comorbidity Scale and the Cumulative Illness Rating Scale – for Geriatrics. Baseline functional capacity was measured using the Duke Activity Status Index. ResultsParticipants’ perceived acceptability of both interventions clustered above the scale midpoint. Most preferred the sitting-to-walking intervention (n = 26; 43.3%). While none of the patient characteristics were associated with intervention acceptability, illness severity (odds ratio = 1.9, p = 0.04) and medications with orthostatic effects (odds ratio = 9.9, p = 0.03) were significantly associated with intervention preference. Conclusions The interventions examined in this study were found to be acceptable to older adults, supporting future research examining their feasibility and effectiveness.
... Conversely, leg muscle activity was higher in overweight adults during standing [31]. However, standing might confer positive [157] or negative [158,159] physiological effects beyond simply EE, and thus a future meta-analysis should evaluate the effects of using standing to break up sitting. ...
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Background: Physical activity (PA) breaks in sitting time might attenuate metabolic markers relevant to the prevention of type 2 diabetes. Objectives: The primary aim of this paper was to systematically review and meta-analyse trials that compared the effects of breaking up prolonged sitting with bouts of PA throughout the day (INT) versus continuous sitting (SIT) on glucose, insulin and triacylglycerol (TAG) measures. A second aim was to compare the effects of INT versus continuous exercise (EX) on glucose, insulin and TAG measures. Methods: The review followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) recommendations. Eligibility criteria consisted of trials comparing INT vs. SIT or INT vs. one bout of EX before or after sitting, in participants aged 18 or above, who were classified as either metabolically healthy or impaired, but not with other major health conditions such as chronic obstructive pulmonary disease or peripheral arterial disease. Results: A total of 42 studies were included in the overall review, whereas a total of 37 studies were included in the meta-analysis. There was a standardised mean difference (SMD) of - 0.54 (95% CI - 0.70, - 0.37, p = 0.00001) in favour of INT compared to SIT for glucose. With respect to insulin, there was an SMD of - 0.56 (95% CI - 0.74, - 0.38, p = 0.00001) in favour of INT. For TAG, there was an SMD of - 0.26 (95% CI - 0.44, - 0.09, p = 0.002) in favour of INT. Body mass index (BMI) was associated with glucose responses (β = - 0.05, 95% CI - 0.09, - 0.01, p = 0.01), and insulin (β = - 0.05, 95% CI - 0.10, - 0.006, p = 0.03), but not TAG (β = 0.02, 95% CI - 0.02, 0.06, p = 0.37). When energy expenditure was matched, there was an SMD of - 0.26 (95% CI - 0.50, - 0.02, p = 0.03) in favour of INT for glucose, but no statistically significant SMDs for insulin, i.e. 0.35 (95% CI - 0.37, 1.07, p = 0.35), or TAG i.e. 0.08 (95% CI - 0.22, 0.37, p = 0.62). It is worth noting that there was possible publication bias for TAG outcomes when PA breaks were compared with sitting. Conclusion: The use of PA breaks during sitting moderately attenuated post-prandial glucose, insulin, and TAG, with greater glycaemic attenuation in people with higher BMI. There was a statistically significant small advantage for PA breaks over continuous exercise for attenuating glucose measures when exercise protocols were energy matched, but no statistically significant differences for insulin and TAG. PROSPERO Registration: CRD42017080982. Prospero registration: CRD42017080982.
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Gravitational stimulation is an inherent part of terrestrial environment. Modified gravity changes functioning of numerous body systems, including cardiovascular system. The aim of this work was to study the mechanisms of vascular modifications induced by modeled microgravity. The human studies were performed using dry immersion. This model is considered as one of the most appropriate to reproduce the effects of prolonged microgravity and especially to mimic the lack of support. We found that dry immersion induces microcirculatory impairment with endothelial dysfunction (study of circulating microparticles) and impaired skin vasodilation (study by iontophoresis of vasoactive substances coupled with laser Doppler flowmetry). This vascular impairment is integrated to more general cardiovascular deconditioning syndrome. The global deconditioning was also considered in this work, including the rapid reset of water and sodium balance to a new steady state. During the recovery period, we observed a significant increase of plasmatic NT-proBNP which might reflect the degree of cardiovascular deconditioning. Our studies with animal models of horizontal and antiorthostatic hypokinesia suggest that increased endotoxin translocation and reduced energy metabolism in microgravity could contribute to endothelial impairment. Endothelial dysfunction may be regarded as one of the therapeutic targets for pathologies associated with physical inactivity and microgravity.
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The effects of a sit-stand-walk intervention to reduce musculoskeletal discomfort, attenuate perceived physical and mental fatigue, and increase physical activity without adversely affecting productivity was investigated for computer-based work. A between-participants design was used with 80 participants randomly assigned to one of five work conditions (sit-stand, stand-sit, sitting, standing and sit-stand-walk) to perform a 60-min computer-based typing transcription task. Musculoskeletal discomfort, and perceived physical and mental fatigue were reported through surveys; productivity was measured by typing speed and typing errors. For the sit-stand-walk intervention musculoskeletal discomfort was significantly less compared to sitting or standing for the hour; perceived physical fatigue was significantly less compared to standing for the hour. There were no benefits or differences among the work conditions in terms of perceived mental fatigue and productivity. By combining postural variability of sit-stand workstations with intermittent light-intensity physical activity enabled by active breaks, the sit-stand-walk intervention demonstrates a beneficial and viable alternative to sedentary office work.
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Purpose Increasing the level of gravity passively on a centrifuge, should be equal to or even more beneficial not only to astronauts living in a microgravity environment but also to patients confined to bed. Gravity therapy (GT) may have beneficial effects on numerous conditions, such as immobility due to neuromuscular disorders, balance disorders, stroke, sports injuries. However, the appropriate configuration for administering the Gz load remains to be determined. Methods To address these issues, we studied graded G-loads from 0.5 to 2.0g in 24 young healthy, male and female participants, trained on a short arm human centrifuge (SAHC) combined with mild activity exercise within 40–59% MHR, provided by an onboard bicycle ergometer. Hemodynamic parameters, as cardiac output (CO), stroke volume (SV), mean arterial pressure (MAP), systolic blood pressure (SBP), diastolic blood pressure (DBP), and heart rate (HR) were analyzed, as well as blood gas analysis. A one-way repeated measures ANOVA and pairwise comparisons were conducted with a level of significance p < 0.05. Results Significant changes in heart rate variability (HRV) and its spectral components (Class, Fmax, and VHF) were found in all g loads when compared to standing ( p < 0.001), except in 1.7 and 2.0g. There were significant changes in CO, cardiac index (CI), and cardiac power (CP) ( p < 0.001), and in MAP ( p = 0.003) at different artificial gravity (AG) levels. Dose-response curves were determined based on statistically significant changes in cardiovascular parameters, as well as in identifying the optimal G level for training, as well as the optimal G level for training. There were statistically significant gender differences in Cardiac Output/CO ( p = 0.002) and Cardiac Power/CP ( p = 0.016) during the AG training as compared to standing. More specifically, these cardiovascular parameters were significantly higher for male than female participants. Also, there was a statistically significant ( p = 0.022) gender by experimental condition interaction, since the high-frequency parameter of the heart rate variability was attenuated during AG training as compared to standing but only for the female participants ( p = 0.004). Conclusion The comprehensive cardiovascular evaluation of the response to a range of graded AG loads, as compared to standing, in male and female subjects provides the dose-response framework that enables us to explore and validate the usefulness of the centrifuge as a medical device. It further allows its use in precisely selecting personalized gravity therapy (GT) as needed for treatment or rehabilitation of individuals confined to bed.
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Major alterations of choroidal cell polarity and protein expression were previously shown to be induced in rats by long-term adaptation to space flight (14 days aboard a space shuttle) or anti-orthostatic suspension (14 and 28 days) performed by tilting rats head-down (i.e. using a ground-based model known to simulate several effects of weightlessness). In rabbits, it was hypothesized that the blood-CSF barrier was opened in choroid plexus, after a short head-down suspension. To understand the early responses to fluid shifts induced by head-down tilts and evaluate the tightness of the choroidal junctions, we have investigated the effects of acute adaptations to anti-orthostatic restraints, using hindlimb-suspended Sprague-Dawley and Wistar rats. Ultrastructural and immunocytochemical studies were performed on choroid plexuses from lateral, third and fourth ventricles, after 30, 90 and 180 minutes of head-down tilt. Alterations were not perceptible at the level of choroidal tight junctions, as shown by freeze-fracture, claudin-1 and ZO-1 immunolocalizations and conventional electron microscopy, after intravenous injection of cytochrome C. The apical surface of choroidal cells was clearly more affected. Microvilli were longer and thinner and ezrin was over-expressed during all the periods of time considered, showing an early cytoskeletal response. Several proteins involved in the choroidal production of cerebrospinal fluid (sodium-potassium ATPase, carbonic anhydrase II, aquaporin 1) appeared first increased (30 minutes after the tilt), and then, returned to the control level or were lowered (after a 3-hour head-down suspension). Although head-down tilts do not seem to damage the blood-cerebrospinal fluid barrier in choroid plexus, it seemed that the expression of several apical proteins is affected very early.
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Many experts believe that artificial gravity will be required for an interplanetary mission. However, despite its attractiveness as an efficient, multi-system countermeasure and its potential for simplifying operational activities, much still needs to be learned regarding the human response to rotating environments before artificial gravity can be successfully implemented. The European Space Agency (ESA) Topical Team on Artificial Gravity recommended a comprehensive program to determine the gravity threshold required to reverse or prevent the detrimental effects of microgravity and to evaluate the effects of centrifugation on various physiological functions. Part of the required research can be accomplished using animal models on a dedicated centrifuge in low Earth orbit. Studies of human responses to centrifugation could be performed during ambulatory, short-and long-duration bed rest, and in-flight studies. Artificial-gravity scenarios should not be a priori discarded in Moon and Mars mission designs. One major step is to determine the relationship between the artificial gravity dose level, duration, and frequency and the physiological responses of the major body functions affected by spaceflight. Once its regime characteristics are defined and a dose–response curve is established, artificial gravity should serve as the standard against which all other countermeasure candidates are evaluated, first on Earth and then in space.
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An international collaborative project, initiated by the DLR-NASA Life Sciences Working Group, led to the performance of a head-down tilt bedrest (HDT) study at the DLR Institute for Aerospace Medicine. Scientific and operational questions were addressed in preparation for the D-2 Spacelab mission. Principal areas of interest were cardiovascular regulation and fluid/electrolyte metabolism. The results are detailed in a series of 13 reports to which the present paper serves as an introduction.
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To determine the effect of posture on maximal O2 uptake (VO2 max) and other cardiorespiratory adaptations to exercise training, 16 male subjects were trained using high-intensity interval and prolonged continuous cycling in either the supine or upright posture 40 min/day 4 days/wk for 8 wk and 7 male subjects served as non-training controls. VO2 max measured during upright cycling and supine cycling, respectively, increased significantly (P less than 0.05) by 16.1 +/- 3.4 and 22.9 +/- 3.4% in the supine training group (STG) and by 14.6 +/- 2.0 and 6.0 +/- 2.0% in the upright training group (UTG). The increase in VO2 max measured during supine cycling was significantly greater (P less than 0.05) in the STG than in the UTG. The increase in VO2 max in the UTG was significantly greater (P less than 0.05) when measured during upright exercise than during supine exercise. However, there was no significant difference in posture-specific VO2 max adaptations in the STG. A postural specificity was also evident in other maximal cardiorespiratory variables (ventilation, CO2 production, and respiratory exchange ratio). In the UTG, maximal heart rate decreased significantly (P less than 0.05) only during supine cycling; there was no significant difference in maximal heart rate after training in the STG. We conclude that posture affects maximal cardiorespiratory adaptations to cycle training. Additionally, supine training is more effective than upright training in increasing maximal cardiorespiratory responses measured during supine exercise, and the effects of supine training generalize to the upright posture to a greater extent than the effects of upright training generalize to the supine posture.(ABSTRACT TRUNCATED AT 250 WORDS)
We studied the effects of head-down tilt bedrest (HDT) on body weight, fluid and sodium homeostasis. A fluid load session with rapid intravenous infusion of 22 ml/kg body weight (BW) isotonic saline was performed before, during and after HDT. During the pre- and post HDT periods the test subjects were given a diet containing 2600 kcal/day. The energy intake was reduced to 2000 kcal/day during HDT. Water intake was kept constant at 40 ml/kg BW, sodium intake was 2.2 mmol/kg BW and protein intake was 1.4 g/kg BW, while the daily fat and carbohydrate intake was reduced during the HDT period. As expected plasma volume and BW changed rapidly in the beginning of HDT and during early recovery. A total body water loss of 0.6 l was observed within the second day after tilting. Plasma volume was reduced by 16% during HDT-bedrest. The time course of the body fluid loss paralleled a decrease in body sodium that then remained fairly constant during the HDT-bedrest period (except for the interference caused by the fluid loading on day S06). A restoration of body fluid and body sodium content occurred early in the recovery period. Fluid loading caused a negative fluid balance of 0.6-0.9 l over a 48 hr period following infusion regardless of the phase of the HDT study. These results demonstrate that under our strictly controlled conditions 1) HDT alters body fluid and sodium balances, 2) a standard fluid loading causes a net negative 3-day fluid balance during all phases of the study.