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Rivas E, Foster J, Crandall CG, Finnerty CC, Suman-Vejas OE. Key Exercise Concepts in the Rehabilitation from Severe Burns. Phys Med Rehabil Clin N Am 2023; 34:811-824. [PMID: 37806699 PMCID: PMC10731385 DOI: 10.1016/j.pmr.2023.05.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/10/2023]
Abstract
This article presents information on the benefits of exercise in counteracting the detrimental effects of bed rest, and/or severe burns. Exercise is key for maintaining physical function, lean body mass, metabolic recovery, and psychosocial health after major burn injuries. The details of an exercise training program conducted in severely burned persons are presented, as well as information on the importance of proper regulation of body temperature during exercise or physical activity. The sections on exercise and thermoregulation are followed by a section on the role of exercise in scarring and contractures. Finally, gaps in the current knowledge of exercise, thermoregulation, and contractures are presented.
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Affiliation(s)
- Eric Rivas
- Microgravity Research, In-Space Solutions, Axiom Space Headquarters, 1290 Hercules Avenue, Houston, TX 77058, USA
| | - Josh Foster
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Institute for Exercise and Environmental Medicine (IEEM), Texas Health Presbyterian Hospital Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA
| | - Craig G Crandall
- Division of Cardiology, Department of Internal Medicine, University of Texas Southwestern Medical Center, Institute for Exercise and Environmental Medicine (IEEM), Texas Health Presbyterian Hospital Dallas, 7232 Greenville Avenue, Suite 435, Dallas, TX 75231, USA
| | - Celeste C Finnerty
- Department of Surgery, Division of Surgical Sciences, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555-1220, USA
| | - Oscar E Suman-Vejas
- Department of Surgery, Division of Surgical Sciences, University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555-1220, USA.
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Saveko A, Bekreneva M, Ponomarev I, Zelenskaya I, Riabova A, Shigueva T, Kitov V, Abu Sheli N, Nosikova I, Rukavishnikov I, Sayenko D, Tomilovskaya E. Impact of different ground-based microgravity models on human sensorimotor system. Front Physiol 2023; 14:1085545. [PMID: 36875039 PMCID: PMC9974674 DOI: 10.3389/fphys.2023.1085545] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Accepted: 01/30/2023] [Indexed: 02/17/2023] Open
Abstract
This review includes current and updated information about various ground-based microgravity models and their impact on the human sensorimotor system. All known models of microgravity are imperfect in a simulation of the physiological effects of microgravity but have their advantages and disadvantages. This review points out that understanding the role of gravity in motion control requires consideration of data from different environments and in various contexts. The compiled information can be helpful to researchers to effectively plan experiments using ground-based models of the effects of space flight, depending on the problem posed.
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Affiliation(s)
- Alina Saveko
- Russian Federation State Scientific Center—Institute of Biomedical Problems of the Russian Academy of Sciences, Moscow, Russia
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Jordan J, Limper U, Tank J. Cardiovascular autonomic nervous system responses and orthostatic intolerance in astronauts and their relevance in daily medicine. Neurol Sci 2022; 43:3039-3051. [PMID: 35194757 PMCID: PMC9018660 DOI: 10.1007/s10072-022-05963-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Accepted: 02/17/2022] [Indexed: 11/12/2022]
Abstract
Background The harsh environmental conditions during space travel, particularly weightlessness, impose a major burden on the human body including the cardiovascular system. Given its importance in adjusting the cardiovascular system to environmental challenges, the autonomic nervous system has been in the focus of scientists and clinicians involved in human space flight. This review provides an overview on human autonomic research under real and simulated space conditions with a focus on orthostatic intolerance. Methods The authors conducted a targeted literature search using Pubmed. Results Overall, 120 articles were identified and included in the review. Conclusions Postflight orthostatic intolerance is commonly observed in astronauts and could pose major risks when landing on another celestial body. The phenomenon likely results from changes in volume status and adaptation of the autonomic nervous system to weightlessness. Over the years, various non-pharmacological and pharmacological countermeasures have been investigated. In addition to enabling safe human space flight, this research may have implications for patients with disorders affecting cardiovascular autonomic control on Earth.
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Affiliation(s)
- Jens Jordan
- Institute of Aerospace Medicine, German Aerospace Center DLR, Linder Hoehe, 51147, Cologne, Germany. .,Aerospace Medicine, Medical Faculty, University of Cologne, Cologne, Germany.
| | - Ulrich Limper
- Institute of Aerospace Medicine, German Aerospace Center DLR, Linder Hoehe, 51147, Cologne, Germany.,Department of Anesthesiology and Intensive Care Medicine, Merheim Medical Center, Hospitals of Cologne, University of Witten/Herdecke, Cologne, Germany
| | - Jens Tank
- Institute of Aerospace Medicine, German Aerospace Center DLR, Linder Hoehe, 51147, Cologne, Germany
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Kramer A, Venegas-Carro M, Zange J, Sies W, Maffiuletti NA, Gruber M, Degens H, Moreno-Villanueva M, Mulder E. Daily 30-min exposure to artificial gravity during 60 days of bed rest does not maintain aerobic exercise capacity but mitigates some deteriorations of muscle function: results from the AGBRESA RCT. Eur J Appl Physiol 2021; 121:2015-2026. [PMID: 33811556 PMCID: PMC8192329 DOI: 10.1007/s00421-021-04673-w] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Accepted: 03/28/2021] [Indexed: 11/29/2022]
Abstract
PURPOSE Spaceflight impairs physical capacity. Here we assessed the protective effect of artificial gravity (AG) on aerobic exercise capacity and muscle function during bed rest, a spaceflight analogue. METHODS 24 participants (33 ± 9 years, 175 ± 9 cm, 74 ± 10 kg, 8 women) were randomly allocated to one of three groups: continuous AG (cAG), intermittent AG (iAG) or control (CTRL). All participants were subjected to 60 days of six-degree head-down tilt bed rest, and subjects of the intervention groups completed 30 min of centrifugation per day: cAG continuously and iAG for 6 × 5 min, with an acceleration of 1g at the center of mass. Physical capacity was assessed before and after bed rest via maximal voluntary contractions, cycling spiroergometry, and countermovement jumps. RESULTS AG had no significant effect on aerobic exercise capacity, flexor muscle function and isometric knee extension strength or rate of force development (RFD). However, AG mitigated the effects of bed rest on jumping power (group * time interaction of the rmANOVA p < 0.001; iAG - 25%, cAG - 26%, CTRL - 33%), plantar flexion strength (group * time p = 0.003; iAG - 35%, cAG - 31%, CTRL - 48%) and plantar flexion RFD (group * time p = 0.020; iAG - 28%, cAG - 12%, CTRL - 40%). Women showed more pronounced losses than men in jumping power (p < 0.001) and knee extension strength (p = 0.010). CONCLUSION The AG protocols were not suitable to maintain aerobic exercise capacity, probably due to the very low cardiorespiratory demand of this intervention. However, they mitigated some losses in muscle function, potentially due to the low-intensity muscle contractions during centrifugation used to avoid presyncope.
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Affiliation(s)
- Andreas Kramer
- Human Performance Research Centre, Department of Sport Science, University of Konstanz, 78457, Konstanz, Germany.
| | - María Venegas-Carro
- Human Performance Research Centre, Department of Sport Science, University of Konstanz, 78457, Konstanz, Germany
| | - Jochen Zange
- Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany
| | - Wolfram Sies
- Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany
| | | | - Markus Gruber
- Human Performance Research Centre, Department of Sport Science, University of Konstanz, 78457, Konstanz, Germany
| | - Hans Degens
- Department of Life Sciences, Manchester Metropolitan University, Manchester, UK.,Institute of Sport Science and Innovations, Lithuanian Sports University, Kaunas, Lithuania
| | - María Moreno-Villanueva
- Human Performance Research Centre, Department of Sport Science, University of Konstanz, 78457, Konstanz, Germany
| | - Edwin Mulder
- Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany
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Ried-Larsen M, Aarts HM, Joyner MJ. Effects of strict prolonged bed rest on cardiorespiratory fitness: systematic review and meta-analysis. J Appl Physiol (1985) 2017; 123:790-799. [DOI: 10.1152/japplphysiol.00415.2017] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2017] [Revised: 06/29/2017] [Accepted: 07/07/2017] [Indexed: 12/29/2022] Open
Abstract
The aim of this systematic review and meta-analysis [International Prospective Register of Systematic Reviews (PROSPERO) CRD42017055619] was to assess the effects of strict prolonged bed rest (without countermeasures) on maximal oxygen uptake (V̇o2max) and to explore sources of variation therein. Since 1949, 80 studies with a total of 949 participants (>90% men) have been published with data on strict bed rest and V̇o2max. The studies were conducted mainly in young participants [median age (interquartile range) 24.5 (22.4–34.0) yr]. The duration of bed rest ranged from 1 to 90 days. V̇o2max declined linearly across bed rest duration. No statistical difference in the decline among studies reporting V̇o2max as l/min (−0.3% per day) compared with studies reporting V̇o2max normalized to body weight (ml·kg−1·min−1; −0.43% per day) was observed. Although both total body weight and lean body mass declined in response to bed rest, we did not see any associations with the decline in V̇o2max. However, 15–26% of the variation in the decline in V̇o2max was explained by the pre-bed-rest V̇o2max levels, independent of the duration of bed rest (i.e., higher pre-bed-rest V̇o2max levels were associated with larger declines in V̇o2max). Furthermore, the systematic review revealed a gap in the knowledge about the cardiovascular response to extreme physical inactivity, particularly in older subjects and women of any age group. In addition to its relevance to spaceflight, this lack of data has significant translational implications because younger women sometimes undergo prolonged periods of bed rest associated with the complications of pregnancy and the incidence of hospitalization including prolonged periods of bed rest increases with age. NEW & NOTEWORTHY Large interindividual responses of maximal oxygen uptake (V̇o2max) to aerobic exercise training exist. However, less is known about the variability in the response of V̇o2max to prolonged bed rest. This systematic review and meta-analysis showed that pre-bed-rest V̇o2max values were inversely associated with the change in V̇o2max independent of the duration of bed rest. Moreover, we identified a large knowledge gap about the causes of decline in V̇o2max, particularly in postmenopausal women, which may have clinical implications.
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Affiliation(s)
- Mathias Ried-Larsen
- Centre for Physical Activity Research, Rigshospitalet, Copenhagen, Denmark; and
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota
| | - Hugo M. Aarts
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota
| | - Michael J. Joyner
- Department of Anesthesiology and Perioperative Medicine, Mayo Clinic, Rochester, Minnesota
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Ade CJ, Broxterman RM, Moore AD, Barstow TJ. Decreases in maximal oxygen uptake following long-duration spaceflight: Role of convective and diffusive O 2 transport mechanisms. J Appl Physiol (1985) 2017; 122:968-975. [PMID: 28153941 DOI: 10.1152/japplphysiol.00280.2016] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2016] [Revised: 12/19/2016] [Accepted: 01/19/2017] [Indexed: 01/22/2023] Open
Abstract
We have previously predicted that the decrease in maximal oxygen uptake (V̇o2max) that accompanies time in microgravity reflects decrements in both convective and diffusive O2 transport to the mitochondria of the contracting myocytes. The aim of this investigation was therefore to quantify the relative changes in convective O2 transport (Q̇o2) and O2 diffusing capacity (Do2) following long-duration spaceflight. In nine astronauts, resting hemoglobin concentration ([Hb]), V̇o2max, maximal cardiac output (Q̇Tmax), and differences in arterial and venous O2 contents ([Formula: see text]-[Formula: see text]) were obtained retrospectively for International Space Station Increments 19-33 (April 2009-November 2012). Q̇o2 and Do2 were calculated from these variables via integration of Fick's Principle of Mass Conservation and Fick's Law of Diffusion. V̇o2max significantly decreased from pre- to postflight (-53.9 ± 45.5%, P = 0.008). The significant decrease in Q̇Tmax (-7.8 ± 9.1%, P = 0.05), despite an unchanged [Hb], resulted in a significantly decreased Q̇o2 (-11.4 ± 10.5%, P = 0.02). Do2 significantly decreased from pre- to postflight by -27.5 ± 24.5% (P = 0.04), as did the peak [Formula: see text]-[Formula: see text] (-9.2 ± 7.5%, P = 0.007). With the use of linear regression analysis, changes in V̇o2max were significantly correlated with changes in Do2 (R2 = 0.47; P = 0.04). These data suggest that spaceflight decreases both convective and diffusive O2 transport. These results have practical implications for future long-duration space missions and highlight the need to resolve the specific mechanisms underlying these spaceflight-induced changes along the O2 transport pathway.NEW & NOTEWORTHY Long-duration spaceflight elicited a significant decrease in maximal oxygen uptake. Given the adverse physiological adaptations to microgravity along the O2 transport pathway that have been reported, an integrative approach to the determinants of postflight maximal oxygen uptake is needed. We demonstrate that both convective and diffusive oxygen transport are decreased following ~6 mo International Space Station missions.
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Affiliation(s)
- C J Ade
- Department of Health and Exercise Science, University of Oklahoma, Norman, Oklahoma; .,Department of Kinesiology, Kansas State University, Manhattan, Kansas
| | - R M Broxterman
- Department of Internal Medicine, University of Utah, Salt Lake City, Utah
| | - A D Moore
- Department of Health and Kinesiology, Lamar University, Beaumont, Texas; and
| | - T J Barstow
- Department of Kinesiology, Kansas State University, Manhattan, Kansas
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Platts SH, Bairey Merz CN, Barr Y, Fu Q, Gulati M, Hughson R, Levine BD, Mehran R, Stachenfeld N, Wenger NK. Effects of sex and gender on adaptation to space: cardiovascular alterations. J Womens Health (Larchmt) 2015; 23:950-5. [PMID: 25401939 DOI: 10.1089/jwh.2014.4912] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Sex and gender differences in the cardiovascular adaptation to spaceflight were examined with the goal of optimizing the health and safety of male and female astronauts at the forefront of space exploration. Female astronauts are more susceptible to orthostatic intolerance after space flight; the visual impairment intracranial pressure syndrome predominates slightly in males. Since spaceflight simulates vascular aging, sex-specific effects on vascular endothelium and thrombotic risk warrant examination as predisposing factors to atherosclerosis, important as the current cohort of astronauts ages. Currently, 20% of astronauts are women, and the recently selected astronaut recruits are 50% women. Thus there should be expectation that future research will reflect the composition of the overall population to determine potential benefits or risks. This should apply both to clinical studies and to basic science research.
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Affiliation(s)
- Steven H Platts
- 1 National Aeronautics and Space Administration Johnson Space Center , Houston, Texas
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Brun CR, Shoemaker JK, Bocking A, Hammond JA, Poole M, Mottola MF. Bed-rest exercise, activity restriction, and high-risk pregnancies: a feasibility study. Appl Physiol Nutr Metab 2011; 36:577-82. [DOI: 10.1139/h11-036] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This feasibility study investigated the response of maternal heart rate, blood pressure, and uterine contractions to a 30-min bed-rest exercise session (while listening to music) in hospitalized women with varying diagnoses of high-risk pregnancy. Eleven antenatal women who were hospitalized for activity restriction were assigned randomly to either a bed-rest exercise and music group (n = 6) or a bed-rest and music group (n = 5) that involved no exercise. The key findings were that there were no changes in maternal blood pressure or in the number of uterine contractions following the exercise intervention. A supervised bed-rest exercise intervention may, therefore, provide minimal risks and help alleviate the physiological effects of hospital activity restriction.
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Affiliation(s)
- Chantale R. Brun
- R. Samuel McLaughlin Foundation-Exercise and Pregnancy Laboratory, University of Western Ontario, London, ON, Canada
- School of Kinesiology, Faculty of Health Sciences, University of Western Ontario, London, ON, Canada
- School of Kinesiology and Recreation, Université de Moncton, Moncton, NB E1A 3E9, Canada
| | - J. Kevin Shoemaker
- School of Kinesiology, Faculty of Health Sciences, University of Western Ontario, London, ON, Canada
| | - Alan Bocking
- St. Joseph’s Health Care London, London, ON, Canada
- Mount Sinai Hospital, University of Toronto, Toronto, ON, Canada
| | - Jo-Anne Hammond
- R. Samuel McLaughlin Foundation-Exercise and Pregnancy Laboratory, University of Western Ontario, London, ON, Canada
- Department of Family Medicine, Schulich School of Medicine & Dentistry, University of Western Ontario, London, ON, Canada
- St. Joseph’s Health Care London, London, ON, Canada
| | - Monica Poole
- St. Joseph’s Health Care London, London, ON, Canada
| | - Michelle F. Mottola
- R. Samuel McLaughlin Foundation-Exercise and Pregnancy Laboratory, University of Western Ontario, London, ON, Canada
- School of Kinesiology, Faculty of Health Sciences, University of Western Ontario, London, ON, Canada
- Department of Anatomy and Cell Biology, Schulich School of Medicine & Dentistry, University of Western Ontario, London, ON, Canada
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Keller DM, Low DA, Davis SL, Hastings J, Crandall CG. Skin surface cooling improves orthostatic tolerance following prolonged head-down bed rest. J Appl Physiol (1985) 2011; 110:1592-7. [PMID: 21454746 DOI: 10.1152/japplphysiol.00233.2010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Prolonged exposure to microgravity, as well as its ground-based analog, head-down bed rest (HDBR), reduces orthostatic tolerance in humans. While skin surface cooling improves orthostatic tolerance, it remains unknown whether this could be an effective countermeasure to preserve orthostatic tolerance following HDBR. We therefore tested the hypothesis that skin surface cooling improves orthostatic tolerance after prolonged HDBR. Eight subjects (six men and two women) participated in the investigation. Orthostatic tolerance was determined using a progressive lower-body negative pressure (LBNP) tolerance test before HDBR during normothermic conditions and on day 16 or day 18 of 6° HDBR during normothermic and skin surface cooling conditions (randomized order post-HDBR). The thermal conditions were achieved by perfusing water (normothermia ∼34°C and skin surface cooling ∼12-15°C) through a tube-lined suit worn by each subject. Tolerance tests were performed after ∼30 min of the respective thermal stimulus. A cumulative stress index (CSI; mmHg LBNP·min) was determined for each LBNP protocol by summing the product of the applied negative pressure and the duration of LBNP at each stage. HDBR reduced normothermic orthostatic tolerance as indexed by a reduction in the CSI from 1,037 ± 96 mmHg·min to 574 ± 63 mmHg·min (P < 0.05). After HDBR, skin surface cooling increased orthostatic tolerance (797 ± 77 mmHg·min) compared with normothermia (P < 0.05). While the reduction in orthostatic tolerance following prolonged HDBR was not completely reversed by acute skin surface cooling, the identified improvements may serve as an important and effective countermeasure for individuals exposed to microgravity, as well as immobilized and bed-stricken individuals.
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Affiliation(s)
- David M Keller
- Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, 7232 Greenville Ave., Dallas, TX 75231, USA
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Lee SMC, Schneider SM, Boda WL, Watenpaugh DE, Macias BR, Meyer RS, Hargens AR. LBNP exercise protects aerobic capacity and sprint speed of female twins during 30 days of bed rest. J Appl Physiol (1985) 2008; 106:919-28. [PMID: 19112155 DOI: 10.1152/japplphysiol.91502.2008] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have shown previously that treadmill exercise within lower body negative pressure (LBNPex) maintains upright exercise capacity (peak oxygen consumption, Vo(2peak)) in men after 5, 15, and 30 days of bed rest (BR). We hypothesized that LBNPex protects treadmill Vo(2peak) and sprint speed in women during a 30-day BR. Seven sets of female monozygous twins volunteered to participate. Within each twin set, one was randomly assigned to a control group (Con) and performed no countermeasures, and the other was assigned to an exercise group (Ex) and performed a 40-min interval (40-80% pre-BR Vo(2peak)) LBNPex (51 +/- 5 mmHg) protocol, plus 5 min of static LBNP, 6 days per week. Before and immediately after BR, subjects completed a 30.5-m sprint test and an upright graded treadmill test to volitional fatigue. These results in women were compared with previously reported reductions in Vo(2peak) and sprint speed in male twins after BR. In women, sprint speed (-8 +/- 2%) and Vo(2peak) (-6 +/- 2%) were not different after BR in the Ex group. In contrast, both sprint speed (-24 +/- 5%) and Vo(2peak) (-16 +/- 3%) were significantly less after BR in the Con group. The effect of BR on sprint speed and Vo(2peak) after BR was not different between women and men. We conclude that treadmill exercise within LBNP protects against BR-induced reductions in Vo(2peak) and sprint speed in women and should prove effective during long-duration spaceflight.
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Affiliation(s)
- Stuart M C Lee
- Cardiovascular Laboratory, Wyle Integrated Science and Engineering Group, Houston, Texas, USA.
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Trappe T, Trappe S, Lee G, Widrick J, Fitts R, Costill D. Cardiorespiratory responses to physical work during and following 17 days of bed rest and spaceflight. J Appl Physiol (1985) 2006; 100:951-7. [PMID: 16306254 DOI: 10.1152/japplphysiol.01083.2005] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To determine the influence of a 17-day exposure to real and simulated spaceflight (SF) on cardiorespiratory function during exercise, four male crewmembers of the STS-78 space shuttle flight and eight male volunteers were studied before, during, and after the 17-day mission and 17 days of −6° head-down-tilt bed rest (BR), respectively. Measurements of oxygen uptake, pulmonary ventilation, and heart rate were made during submaximal cycling 60, 30, and 15 days before the SF liftoff and 12 and 7 days before BR; on SF days 2, 8, and 13 and on BR days 2, 8, and 13; and on days 1, 4, 5, and 8 after return to Earth and on days 3 and 7 after BR. During 15 days before liftoff, day 4 after return, and day 8 after return and all BR testing, each subject completed a continuous exercise test to volitional exhaustion on a semirecumbent (SF) or supine (BR) cycle ergometer to determine the submaximal and maximal cardiorespiratory responses to exercise. The remaining days of the SF testing were limited to a workload corresponding to 85% of the peak pre-SF peak oxygen uptake (V̇o2 peak) workload. Exposure to and recovery from SF and BR induced similar responses to submaximal exercise at 150 W. V̇o2 peak decreased by 10.4% from pre-SF (15 days before liftoff) to day 4 after return and 6.6% from pre-BR to day 3 after return, which was partially (SF: −5.2%) or fully (BR) restored within 1 wk of recovery. Workload corresponding to 85% of the peak pre-SF V̇o2 peak showed a rapid and continued decline throughout the flight (SF day 2, −6.2%; SF day 8, −9.0%), reaching a nadir of −11.3% during testing on SF day 13. During BR, V̇o2 peak also showed a decline from pre-BR (BR day 2, −7.3%; BR day 8, −7.1%; BR day 13, −9.0%). These results suggest that the onset of and recovery from real and simulated microgravity-induced cardiorespiratory deconditioning is relatively rapid, and head-down-tilt BR appears to be an appropriate model of this effect, both during and after SF.
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Affiliation(s)
- Todd Trappe
- Human Performance Laboratory, Ball State Univ., Muncie, IN 47306, USA.
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Harm DL, Jennings RT, Meck JV, Powell MR, Putcha L, Sams CP, Schneider SM, Shackelford LC, Smith SM, Whitson PA. Invited review: gender issues related to spaceflight: a NASA perspective. J Appl Physiol (1985) 2001; 91:2374-83. [PMID: 11641383 DOI: 10.1152/jappl.2001.91.5.2374] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This minireview provides an overview of known and potential gender differences in physiological responses to spaceflight. The paper covers cardiovascular and exercise physiology, barophysiology and decompression sickness, renal stone risk, immunology, neurovestibular and sensorimotor function, nutrition, pharmacotherapeutics, and reproduction. Potential health and functional impacts associated with the various physiological changes during spaceflight are discussed, and areas needing additional research are highlighted. Historically, studies of physiological responses to microgravity have not been aimed at examining gender-specific differences in the astronaut population. Insufficient data exist in most of the discipline areas at this time to draw valid conclusions about gender-specific differences in astronauts, in part due to the small ratio of women to men. The only astronaut health issue for which a large enough data set exists to allow valid conclusions to be drawn about gender differences is orthostatic intolerance following shuttle missions, in which women have a significantly higher incidence of presyncope during stand tests than do men. The most common observation across disciplines is that individual differences in physiological responses within genders are usually as large as, or larger than, differences between genders. Individual characteristics usually outweigh gender differences per se.
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Affiliation(s)
- D L Harm
- Human Adaptation and Countermeasures Office, NASA Johnson Space Center, Houston, TX 77058, USA.
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Smorawiński J, Nazar K, Kaciuba-Uscilko H, Kamińska E, Cybulski G, Kodrzycka A, Bicz B, Greenleaf JE. Effects of 3-day bed rest on physiological responses to graded exercise in athletes and sedentary men. J Appl Physiol (1985) 2001; 91:249-57. [PMID: 11408437 DOI: 10.1152/jappl.2001.91.1.249] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To test the hypotheses that short-term bed-rest (BR) deconditioning influences metabolic, cardiorespiratory, and neurohormonal responses to exercise and that these effects depend on the subjects' training status, 12 sedentary men and 10 endurance- and 10 strength-trained athletes were submitted to 3-day BR. Before and after BR they performed incremental exercise test until volitional exhaustion. Respiratory gas exchange and heart rate (HR) were recorded continuously, and stroke volume (SV) was measured at submaximal loads. Blood was taken for lactate concentration ([LA]), epinephrine concentration ([Epi]), norepinephrine concentration ([NE]), plasma renin activity (PRA), human growth hormone concentration ([hGH]), testosterone, and cortisol determination. Reduction of peak oxygen uptake (VO(2 peak)) after BR was greater in the endurance athletes than in the remaining groups (17 vs. 10%). Decrements in VO(2 peak) correlated positively with the initial values (r = 0.73, P < 0.001). Resting and exercise respiratory exchange ratios were increased in athletes. Cardiac output was unchanged by BR in all groups, but exercise HR was increased and SV diminished in the sedentary subjects. The submaximal [LA] and [LA] thresholds were decreased in the endurance athletes from 71 to 60% VO(2 peak) (P < 0.001); they also had an earlier increase in [NE], an attenuated increase in [hGH], and accentuated PRA and cortisol elevations during exercise. These effects were insignificant in the remaining subjects. In conclusion, reduction of exercise performance and modifications in neurohormonal response to exercise after BR depend on the previous level and mode of physical training, being the most pronounced in the endurance athletes.
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Affiliation(s)
- J Smorawiński
- Department of Sport Medicine, Academy of Physical Education, 61-871 Poznan, Poland
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16
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Millet C, Custaud MA, Maillet A, Allevard AM, Duvareille M, Gauquelin-Koch G, Gharib C, Fortrat JO. Endocrine responses to 7 days of head-down bed rest and orthostatic tests in men and women. CLINICAL PHYSIOLOGY (OXFORD, ENGLAND) 2001; 21:172-83. [PMID: 11318825 DOI: 10.1046/j.1365-2281.2001.00315.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The objective of this study was to investigate plasma volume (PV), total body water, hormones and hydroelectrolyte responses in eight males (25-40 years) and eight females (25-31 years) during 7 days of exposure to simulated microgravity (-6 degrees head-down bed rest, HDBR). Bed rest is a model that has commonly been used to simulate spaceflight. Heart rate (HR), blood pressure (BP) and vasoactive hormone responses were studied before and after HDBR during a 10-min stand test. No change in total body water and body mass was noted in either sex. The decrease in PV was similar in both men (9.1 +/- 1.4%) and women (9.4 +/- 0.8%). Urinary normetanephrine (NMN) was decreased during HDBR in both sexes. Urinary metanephrine (MN) and plasma catecholamines were unchanged. Daily urinary excretion of urea, an indirect index of protein breakdown, was increased only in the female subjects during HDBR. Plasma active renin (AR) and aldosterone were increased in both sexes, but urinary atrial natriuretic peptide (ANP) and arginine vasopressin (AVP) were unchanged throughout the study. Also, the hormonal responses to 7 days of HDBR were comparable between men and women. Moreover, the results show similar cardiovascular and endocrine responses to standing after HDBR. However, the orthostatic intolerance following HDBR was associated with a blunted increase in noradrenaline (NA) only in the women during the stand test. It is concluded that: (i) 7 days of physical inactivity achieved during HDBR resulted in a reduced sympathetic activity in both sexes and alterations in protein metabolism in women and (ii) standing after HDBR resulted in an attenuated release of noradrenaline in women.
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Affiliation(s)
- C Millet
- Laboratoire de Physiologie de l'Environnement (Equipe Accueil 645), Groupement d'Intérêt Public Exercice, Faculté de Médecine, 69373 Lyon cedex 08, France
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17
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Convertino VA, Bloomfield SA, Greenleaf JE. An overview of the issues: physiological effects of bed rest and restricted physical activity. Med Sci Sports Exerc 1997; 29:187-90. [PMID: 9044221 DOI: 10.1097/00005768-199702000-00004] [Citation(s) in RCA: 179] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Reduction of exercise capacity with confinement to bed rest is well recognized. Underlying physiological mechanisms include dramatic reductions in maximal stroke volume, cardiac output, and oxygen uptake. However, bed rest by itself does not appear to contribute to cardiac dysfunction. Increased muscle fatigue is associated with reduced muscle blood flow, red cell volume, capillarization and oxidative enzymes. Loss of muscle mass and bone density may be reflected by reduced muscle strength and higher risk for injury to bones and joints. The resultant deconditioning caused by bed rest can be independent of the primary disease and physically debilitating in patients who attempt to reambulate to normal active living and working. A challenge to clinicians and health care specialists has been the identification of appropriate and effective methods to restore physical capacity of patients during or after restricted physical activity associated with prolonged bed rest. The examination of physiological responses to bed rest deconditioning and exercise training in healthy subjects has provided significant information to develop effective rehabilitation treatments. The successful application of acute exercise to enhance orthostatic stability, daily endurance exercise to maintain aerobic capacity, or specific resistance exercises to maintain musculoskeletal integrity rather than the use of surgical, pharmacological, and other medical treatments for clinical conditions has been enhanced by investigation and understanding of underlying mechanisms that distinguish physical deconditioning from the disease. This symposium presents an overview of cardiovascular and musculoskeletal deconditioning associated with reduced physical work capacity following prolonged bed rest and exercise training regimens that have proven successful in ameliorating or reversing these adverse effects.
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Affiliation(s)
- V A Convertino
- Physiology Research Branch, Clinical Sciences Division, Brooks Air Force Base, TX 78235, USA
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18
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Abstract
Maximal oxygen uptake (VO2max) is reduced in healthy individuals confined to bed rest, suggesting it is independent of any disease state. The magnitude of reduction in VO2max is dependent on duration of bed rest and the initial level of aerobic fitness (VO2max), but it appears to be independent of age or gender. Bed rest induces an elevated maximal heart rate which, in turn, is associated with decreased cardiac vagal tone, increased sympathetic catecholamine secretion, and greater cardiac beta-receptor sensitivity. Despite the elevation in heart rate, VO2max is reduced primarily from decreased maximal stroke volume and cardiac output. An elevated ejection fraction during exercise following bed rest suggests that the lower stroke volume is not caused by ventricular dysfunction but is primarily the result of decreased venous return associated with lower circulating blood volume, reduced central venous pressure, and higher venous compliance in the lower extremities. VO2max, stroke volume, and cardiac output are further compromised by exercise in the upright posture. The contribution of hypovolemia to reduced cardiac output during exercise following bed rest is supported by the close relationship between the relative magnitude (% delta) and time course of change in blood volume and VO2max during bed rest, and also by the fact that retention of plasma volume is associated with maintenance of VO2max after bed rest. Arteriovenous oxygen difference during maximal exercise is not altered by bed rest, suggesting that peripheral mechanisms may not contribute significantly to the decreased VO2max. However reduction in baseline and maximal muscle blood flow, red blood cell volume, and capillarization in working muscles represent peripheral mechanisms that may contribute to limited oxygen delivery and, subsequently, lowered VO2max. Thus, alterations in cardiac and vascular functions induced by prolonged confinement to bed rest contribute to diminution of maximal oxygen uptake and reserve capacity to perform physical work.
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Affiliation(s)
- V A Convertino
- Physiology Research Branch, Clinical Sciences Division, Brooks Air Force Base, TX 78235, USA
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19
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Affiliation(s)
- V A Convertino
- Physiology Research Branch, Brooks Air Force Base, TX 78235, USA
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20
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Suzuki Y, Kashihara H, Takenaka K, Kawakubo K, Makita Y, Goto S, Ikawa S, Gunji A. Effects of daily mild supine exercise on physical performance after 20 days bed rest in young persons. ACTA ASTRONAUTICA 1994; 33:101-111. [PMID: 11539509 DOI: 10.1016/0094-5765(94)90114-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
To investigate the effects of daily mild supine exercise on physical performance capacity identified as maximal oxygen uptake rate (VO2max) after 20 days bedrest, 3 male students performed a supine pedaling at 40% intensity of VO2max for one hour every day, while 6 male and 5 female students were control. Before and after the bedrest, muscle mass and strength of exercising leg and cardiovascular responses during -40mmHg lower body negative pressure (LBNP) and moderate upright cycling exercise were measured. Despite the exercise programme VO2max was similarly decreased to the control subjects after bed-rest. The delta VO2max was correlated to delta % left ventricular fractional shortening during LBNP, and also % delta VO2max to % delta stroke volume of the moderate exercise (both p<0.05). The exercise programme should be too weak to maintain cardiovascular functions and thus to present the decrease in VO2max against prolonged bedrest as well as weightlessness stress.
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Affiliation(s)
- Y Suzuki
- Department of Health Administration, University of Tokyo, Japan
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21
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Vernikos J, Dallman MF, Keil LC, O'Hara D, Convertino VA. Gender differences in endocrine responses to posture and 7 days of -6 degrees head-down bed rest. THE AMERICAN JOURNAL OF PHYSIOLOGY 1993; 265:E153-61. [PMID: 8338147 DOI: 10.1152/ajpendo.1993.265.1.e153] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Endocrine regulation of fluids and electrolytes during 7 days of -6 degrees head-down bed rest (HDBR) was compared in male (n = 8) and, for the first time, female (n = 8) volunteers. The subjects' responses to quiet standing for 2 h before and after HDBR were also tested. In both sexes, diuresis and natriuresis were evident during the first 2-3 days of HDBR, resulting in a marked increase in the urinary Na(+)-to-K+ ratio and significant Na+ retention on re-ambulation. After the 1st day of HDBR, plasma renin activity (PRA) was increased relative to aldosterone (Aldo), plasma volume was decreased, and the renal response to Aldo appeared to be appropriate. Circulating levels of arginine vasopressin, cortisol, and ACTH were unchanged during HDBR. Plasma testosterone decreased slightly on day 2 of HDBR in males. The ratio of early morning ACTH to cortisol was lower in females than in males because ACTH was lower in females. Urinary cortisol increased and remained elevated throughout the HDBR in males only. There were no gender differences in the responses to 7 days of HDBR, except those in the pituitary-adrenal system; those differences appeared unrelated to the postural change. The provocative cardiovascular test of quiet standing before and after HDBR revealed both sex differences and effects of HDBR. There were significant sex differences in cardiovascular responses to standing before and after HDBR. Females had greater PRA and Aldo responses to standing before HDBR and larger Aldo responses to standing after HDBR than males.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- J Vernikos
- Life Science Division, National Aeronautics and Space Administration-Ames Research Center, Moffett Field 94035
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22
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Abstract
Of 12 healthy men with a mean age 50 +/- 4 years who had been at bed rest for 10 days, six were randomly assigned to perform individually prescribed physical exercise daily for 60 days after bed rest (exercise group) and six simply resumed their customary activities (control group). Exercise group subjects were significantly more active than control subjects during this interval (p less than .05). Two classic training effects observed in the 60 days after bed rest were significantly larger among exercise than among control group subjects; compared with values immediately after bed rest, heart rate at a constant submaximal workload declined by 36 +/- 11 beats/min in the exercise group vs 16 +/- 8 beats/min in the control group and peak oxygen consumption increased by 4.8 +/- 4.2 vs 2.2 +/- 5.0 ml/kg/min (both p less than .05). Despite these differences in the cardiovascular response to exercise, peak oxygen consumption in both groups returned to before-bed rest levels by 30 days after bed rest, and this was accompanied by significant (p less than .05) and similar increases in resting left ventricular end-diastolic and stroke volumes in both groups. Simple resumption of usual physical activities after bed rest was as effective as formal exercise conditioning in restoring functional capacity to before-bed rest levels.
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Hung J, Goldwater D, Convertino VA, McKillop JH, Goris ML, DeBusk RF. Mechanisms for decreased exercise capacity after bed rest in normal middle-aged men. Am J Cardiol 1983; 51:344-8. [PMID: 6823849 DOI: 10.1016/s0002-9149(83)80063-0] [Citation(s) in RCA: 62] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
The mechanisms responsible for the decrease in exercise capacity after bed rest were assessed in 12 apparently healthy men aged 50 +/- 4 years who underwent equilibrium gated blood pool scintigraphy during supine and upright multistage bicycle ergometry before and after 10 days of bed rest. After bed rest, echocardiographically measured supine resting left ventricular end-diastolic volume decreased by 16% (p less than 0.05). Peak oxygen uptake during supine effort after bed rest was diminished by 6% (p = not significant [NS]), whereas peak oxygen uptake during upright effort declined by 15% (p less than 0.05). After bed rest, increases in heart rate were also greater during exercise in the upright than in the supine position (p less than 0.05). Values of left ventricular ejection fraction increased normally during both supine and upright effort after bed rest and were higher than corresponding values before bed rest (p less than 0.05). After bed rest, increased left ventricular ejection fraction and heart rate largely compensated for the reduced cardiac volume during supine effort, but these mechanisms were insufficient to maintain oxygen transport capacity at levels during upright effort before bed rest. These results indicate that orthostatically induced cardiac underfilling, not physical deconditioning or left ventricular dysfunction, is the major cause of reduced effort tolerance after 10 days of bed rest in normal middle-aged men.
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Convertino V, Hung J, Goldwater D, DeBusk RF. Cardiovascular responses to exercise in middle-aged men after 10 days of bedrest. Circulation 1982; 65:134-40. [PMID: 6796287 DOI: 10.1161/01.cir.65.1.134] [Citation(s) in RCA: 104] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The cardiorespiratory response to 10 days of continuous recumbency was assessed in 12 healthy men, age 50 +/- 4 years, who underwent supine and upright graded maximal exercise testing before and after bedrest. The decrease in peak oxygen uptake after bedrest was greater during upright exercise (15.1%, p less than 0.05) than during supine exercise (6.1%, NS): from 25.8 +/- 5.2 to 21.9 +/- 4.5 ml/kg/min and from 24.6 +/- 5.2 to 23.1 +/- 4.8 ml/kg/min. The decrease in submaximal work was also greater in the upright than in the supine position ( p less than 0.05). Ventilation volume was significantly elevated (p less than 0.05) after bedrest during maximal and submaximal effort in both the supine and upright positions. After bedrest, peak heart rate increased 5.7% and 5.9% during supine and upright testing, respectively (p less than 0.05). The increases in rate-pressure product after bedrest were significantly larger (p less than 0.05) during upright than during supine exercise. These results indicate that orthostatic stress is the most important factor limiting exercise tolerance after bedrest in normal middle-aged men. This mechanism also increases the myocardial oxygen demands during submaximal effort after bedrest. Intermittent exposure to gravitational stress during the bedrest stage of hospital convalescence may obviate much of the deterioration in cardiovascular performance that follows myocardial infarction.
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