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1
Arbogast, Sandrine, Jacqueline Smith, Yves Matuszczak, Brian J. Hardin, Jennifer S. Moylan, Jeffrey D. Smith, Jeffrey Ware, Ann R. Kennedy et Michael B. Reid. « Bowman-Birk inhibitor concentrate prevents atrophy, weakness, and oxidative stress in soleus muscle of hindlimb-unloaded mice ». Journal of Applied Physiology 102, no 3 (mars 2007) : 956–64. http://dx.doi.org/10.1152/japplphysiol.00538.2006.
Texte intégralRésumé :
Antigravity muscles atrophy and weaken during prolonged mechanical unloading caused by bed rest or spaceflight. Unloading also induces oxidative stress in muscle, a putative cause of weakness. We tested the hypothesis that dietary supplementation with Bowman-Birk inhibitor concentrate (BBIC), a soy protein extract, would oppose these changes. Adult mice were fed a diet supplemented with 1% BBIC during hindlimb unloading for up to 12 days. Soleus muscles of mice fed the BBIC-supplemented diet weighed less, developed less force per cross-sectional area, and developed less total force after unloading than controls. BBIC supplementation was protective, blunting decrements in soleus muscle weight and force. Cytosolic oxidant activity was assessed using 2′,7′-dichlorofluorescin diacetate. Oxidant activity increased in unloaded muscle, peaking at 3 days and remaining elevated through 12 days of unloading. Increases in oxidant activity correlated directly with loss of muscle mass and were abolished by BBIC supplementation. In vitro assays established that BBIC directly buffers reactive oxygen species and also inhibits serine protease activity. We conclude that dietary supplementation with BBIC protects skeletal muscle during prolonged unloading, promoting redox homeostasis in muscle fibers and blunting atrophy-induced weakness.
2
Marusic, Uros, Marco Narici, Bostjan Simunic, Rado Pisot et Ramona Ritzmann. « Nonuniform loss of muscle strength and atrophy during bed rest : a systematic review ». Journal of Applied Physiology 131, no 1 (1 juillet 2021) : 194–206. http://dx.doi.org/10.1152/japplphysiol.00363.2020.
Texte intégralRésumé :
Our study contributes to the characterization of muscle loss and weakness processes reflected by a logarithmic decline in muscle strength induced by chronic bed rest. Acute short-term hospitalization (≤5 days) associated with periods of disuse/immobilization/prolonged time in the supine position in the hospital bed is sufficient to significantly decrease muscle mass and size and induce functional changes related to weakness in maximal muscle strength. By bringing together integrated evaluation of muscle structure and function, this work identifies that 79% of the loss in muscle strength can be explained by muscle atrophy, leaving 21% of the functional loss unexplained. The outcomes of this study should be considered in the development of daily countermeasures for preserving neuromuscular integrity as well as preconditioning interventions to be implemented before clinical bed rest or chronic gravitational unloading (e.g., spaceflights).
3
Lovejoy, Jennifer C., Steven R. Smith, Jeffrey J. Zachwieja, George A. Bray, Marlene M. Windhauser, Peter J. Wickersham, Johannes D. Veldhuis, Richard Tulley et Jacques A. de la Bretonne. « Low-dose T3 improves the bed rest model of simulated weightlessness in men and women ». American Journal of Physiology-Endocrinology and Metabolism 277, no 2 (1 août 1999) : E370—E379. http://dx.doi.org/10.1152/ajpendo.1999.277.2.e370.
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This study tested the hypothesis that low-dose 3,5,3′-triiodothyronine (T3) administration during prolonged bed rest improves the ground-based model of spaceflight. Nine men (36.4 ± 1.3 yr) and five women (34.2 ± 2.1 yr) were studied. After a 5-day inpatient baseline period, subjects were placed at total bed rest with 6° head-down tilt for 28 days followed by 5-day recovery. Fifty micrograms per day of T3( n = 8) or placebo ( n = 6) were given during bed rest. Serum T3 concentrations increased twofold, whereas thyroid-stimulating hormone was suppressed in treated subjects. T3-treated subjects showed significantly greater negative nitrogen balance and lost more weight ( P = 0.02) and lean mass ( P < 0.0001) than placebo subjects. Protein breakdown (whole body [13C]leucine kinetics) increased 31% in the T3 group but only 8% in the placebo group. T3-treated women experienced greater changes in leucine turnover than men, despite equivalent weight loss. Insulin sensitivity fell by 50% during bed rest in all subjects ( P = 0.005), but growth hormone release and insulin release were largely unaffected. In conclusion, addition of low-dose T3 to the bed rest model of muscle unloading improves the ground-based simulation of spaceflight and unmasks several important gender differences.
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Westby, Christian M., David S. Martin, Stuart M. C. Lee, Michael B. Stenger et Steven H. Platts. « Left ventricular remodeling during and after 60 days of sedentary head-down bed rest ». Journal of Applied Physiology 120, no 8 (15 avril 2016) : 956–64. http://dx.doi.org/10.1152/japplphysiol.00676.2015.
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Short periods of weightlessness are associated with reduced stroke volume and left ventricular (LV) mass that appear rapidly and are thought to be largely dependent on plasma volume. The magnitude of these cardiac adaptations are even greater after prolonged periods of simulated weightlessness, but the time course during and the recovery from bed rest has not been previously described. We collected serial measures of plasma volume (PV, carbon monoxide rebreathing) and LV structure and function [tissue Doppler imaging, three-dimensional (3-D) and 2-D echocardiography] before, during, and up to 2 wk after 60 days of 6° head down tilt bed rest (HDTBR) in seven healthy subjects (four men, three women). By 60 days of HDTBR, PV was markedly reduced (2.7 ± 0.3 vs. 2.3 ± 0.3 liters, P < 0.001). Resting measures of LV volume and mass were ∼15% ( P < 0.001) and ∼14% lower ( P < 0.001), respectively, compared with pre-HDTBR values. After 3 days of reambulation, both PV and LV volumes were not different than pre-HDTBR values. However, LV mass did not recover with normalization of PV and remained 12 ± 4% lower than pre-bed rest values ( P < 0.001). As previously reported, decreased PV and LV volume precede and likely contribute to cardiac atrophy during prolonged LV unloading. Although PV and LV volume recover rapidly after HDTBR, there is no concomitant normalization of LV mass. These results demonstrate that reduced LV mass in response to prolonged simulated weightlessness is not a simple effect of tissue dehydration, but rather true LV muscle atrophy that persists well into recovery.
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Mazzatti, Dawn J., Melissa A. Smith, Radu C. Oita, Fei-Ling Lim, Andrew J. White et Michael B. Reid. « Muscle unloading-induced metabolic remodeling is associated with acute alterations in PPARδ and UCP-3 expression ». Physiological Genomics 34, no 2 (juillet 2008) : 149–61. http://dx.doi.org/10.1152/physiolgenomics.00281.2007.
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A number of physiological changes follow prolonged skeletal muscle unloading as occurs in spaceflight, bed rest, and hindlimb suspension (HLS) and also in aging. These include muscle atrophy, fiber type switching, and loss of the ability to switch between lipid and glucose usage, or metabolic inflexibility. The signaling and genomic events that precede these physiological manifestations have not been investigated in detail, particularly in regard to loss of metabolic flexibility. Here we used gene arrays to determine the effects of 24-h HLS on metabolic remodeling in mouse muscle. Acute unloading resulted in differential expression of a number of transcripts in soleus and gastrocnemius muscle, including many involved in lipid and glucose metabolism. These include the peroxisome proliferator-activated receptors (PPARs). In contrast to Ppar-α and Ppar-γ, which were downregulated by acute HLS, Ppar-δ was upregulated concomitant with increased expression of its downstream target, uncoupling protein-3 ( Ucp-3). However, differential expression of Ppar-δ was both acute and transient in nature, suggesting that regulation of PPARδ may represent an adaptive, compensatory response aimed at regulating fuel utilization and maintaining metabolic flexibility.
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Radek, Katherine A., Lisa A. Baer, Jennifer Eckhardt, Luisa A. DiPietro et Charles E. Wade. « Mechanical unloading impairs keratinocyte migration and angiogenesis during cutaneous wound healing ». Journal of Applied Physiology 104, no 5 (mai 2008) : 1295–303. http://dx.doi.org/10.1152/japplphysiol.00977.2007.
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Although initially thought to improve an individual's ability to heal, mechanical unloading promoted by extended periods of bed rest has emerged as a contributing factor to delayed or aberrant tissue repair. Using a rat hindlimb unloading (HLU) model of hypogravity, we mimicked some aspects of physical inactivity by removing weight-bearing loads from the hindlimbs and producing a systemic cephalic fluid shift. This model simulates bed rest in that the animal undergoes physiological adaptations, resulting in a reduction in exercise capability, increased frequency of orthostatic intolerance, and a reduction in plasma volume. To investigate whether changes associated with prior prolonged bed rest correlate with impaired cutaneous wound healing, we examined wound closure, angiogenesis, and collagen content in day 2 to day 21 wounds from rats exposed to HLU 2 wk before excisional wounding. Wound closure was delayed in day 2 wounds from HLU rats compared with ambulatory controls. Although the levels of proangiogenic growth factors, fibroblast growth factor-2 (FGF-2), and vascular endothelial growth factor (VEGF) were similar between the two groups, wound vascularity was significantly reduced in day 7 wounds from HLU animals. To further examine this disparity, total collagen content was assessed but found to be similar between the two groups. Taken together, these results suggest that keratinocyte and endothelial cell function may be impaired during the wound healing process under periods of prolonged inactivity or bed rest.
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Yamashita-Goto, Katsumasa, Ryoko Okuyama, Masanori Honda, Kensuke Kawasaki, Kazuhiko Fujita, Takahiro Yamada, Ikuya Nonaka, Yoshinobu Ohira et Toshitada Yoshioka. « Maximal and submaximal forces of slow fibers in human soleus after bed rest ». Journal of Applied Physiology 91, no 1 (1 juillet 2001) : 417–24. http://dx.doi.org/10.1152/jappl.2001.91.1.417.
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The effects of 2 and 4 mo of bed rest, with or without exercise countermeasures, on the contractile properties of slow fibers in the human soleus muscle were examined. Mean fiber diameters were 8 and 36% smaller after 2 and 4 mo of bed rest, respectively, than the pre-bed rest level. Maximum tetanic force (Po), maximum activated force (Fmax) per cross-sectional area (CSA), and the common-logarithm value of free Ca2+concentration required for half-maximal activation (pCa50) also decreased after 2 and 4 mo of bed rest. In contrast, maximum unloaded shortening velocity ( V o) was increased after 2 and 4 mo of bed rest. After 1 mo of recovery, fiber diameters, Po, Fmax per CSA ( P > 0.05), and pCa50 were increased and V odecreased toward pre-bed rest levels. Effects of knee extension/flexion exercise by wearing an anti-G Penguin suit for 10 h daily, and the effects of loading or unloading of the plantar flexors with (Penguin-1) or without (Penguin-2) placing the elastic loading elements of the suit, respectively, were investigated during ∼2 mo of bed rest. In the Penguin-1 group, mean fiber diameter, Po, Fmax per CSA, V o, and pCa50 were similar before and after bed rest. However, the responses of fiber size and contractile properties to bed rest were not prevented in the Penguin-2 group, although the degree of the changes was less than those induced by bed rest without any countermeasure. These results indicate that long-term bed rest results in reductions of fiber size, force-generation capacity, and Ca2+sensitivity, and enhancement of shortening velocity in slow fibers of the soleus. The data indicate that continuous mechanical loading on muscle, such as stretching of muscle, is an effective countermeasure for the prevention of muscular adaptations to gravitational unloading.
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Clarke, Mark S. F., Marcas M. Bamman et Daniel L. Feeback. « Bed rest decreases mechanically induced myofiber wounding and consequent wound-mediated FGF release ». Journal of Applied Physiology 85, no 2 (1 août 1998) : 593–600. http://dx.doi.org/10.1152/jappl.1998.85.2.593.
Texte intégralRésumé :
Using a terrestrial model of spaceflight (i.e., bed rest), we investigated the amount of myofiber wounding and fibroblast growth factor (FGF) release that occurs during unloading. Myofiber wounding was determined by serum levels of the creatine kinase MM (CKMM) isoform before and after bed rest. Serum levels of both acidic FGF (aFGF) and basic FGF were also determined. A second group of subjects was treated in an identical fashion except that they underwent a resistive exercise program during bed rest. Bed rest alone caused significant ( P < 0.05; n = 7) reductions in post-bed-rest serum levels of both CKMM and aFGF, which were paralleled by a significant ( P < 0.05; n = 7) decrease in myofiber size. In contrast, bed rest plus resistive exercise resulted in significant ( P < 0.05; n = 7) increases in post-bed-rest serum levels of both CKMM and aFGF, which were paralleled by inhibition of the atrophic response. These results suggest that mechanically induced, myofiber wound-mediated FGF release may play an important role in the etiology of unloading-induced skeletal muscle atrophy.
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Rullman, Eric, Rodrigo Fernandez-Gonzalo, Igor B. Mekjavić, Thomas Gustafsson et Ola Eiken. « MEF2 as upstream regulator of the transcriptome signature in human skeletal muscle during unloading ». American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 315, no 4 (1 octobre 2018) : R799—R809. http://dx.doi.org/10.1152/ajpregu.00452.2017.
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Our understanding of skeletal muscle structural and functional alterations during unloading has increased in recent decades, yet the molecular mechanisms underpinning these changes have only started to be unraveled. The purpose of the current investigation was to assess changes in skeletal muscle gene expression after 21 days of bed rest, with a particular focus on predicting upstream regulators of muscle disuse. Additionally, the association between differential microRNA expression and the transcriptome signature of bed rest were investigated. mRNAs from musculus vastus lateralis biopsies obtained from 12 men before and after the bed rest were analyzed using a microarray. There were 54 significantly upregulated probesets after bed rest, whereas 103 probesets were downregulated (false discovery rate 10%; fold-change cutoff ≥1.5). Among the upregulated genes, transcripts related to denervation-induced alterations in skeletal muscle were identified, e.g., acetylcholine receptor subunit delta and perinatal myosin. The most downregulated transcripts were functionally enriched for mitochondrial genes and genes involved in mitochondrial biogenesis, followed by a large number of contractile fiber components. Upstream regulator analysis identified a robust inhibition of the myocyte enhancer factor-2 (MEF2) family, in particular MEF2C, which was suggested to act upstream of several key downregulated genes, most notably peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α)/peroxisome proliferator-activated receptors (PPARs) and CRSP3. Only a few microRNAs were identified as playing a role in the overall transcriptome picture induced by sustained bed rest. Our results suggest that the MEF2 family is a key regulator underlying the transcriptional signature of bed rest and, hence, ultimately also skeletal muscle alterations induced by systemic unloading in humans.
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Belavý, Daniel L., Carolyn A. Richardson, Stephen J. Wilson, Dieter Felsenberg et Jörn Rittweger. « Tonic-to-phasic shift of lumbo-pelvic muscle activity during 8 weeks of bed rest and 6-months follow up ». Journal of Applied Physiology 103, no 1 (juillet 2007) : 48–54. http://dx.doi.org/10.1152/japplphysiol.00850.2006.
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Prior motor control studies in unloading have shown a tonic-to-phasic shift in muscle activation, particularly in the short extensors. Tonic muscle activity is considered critical for normal musculoskeletal function. The shift from tonic-to-phasic muscle activity has not been systematically studied in humans in unloading nor at the lumbo-pelvic (LP) region. Ten healthy young male subjects underwent 8 wk of bed rest with 6-mo follow up as part of the “Berlin Bed-Rest Study.” A repetitive knee movement model performed in the prone position is used to stimulate tonic holding LP muscle activity, as measured by superficial EMG. Tonic and phasic activation patterns were quantified by relative height of burst vs. baseline electromyographic linear-envelope signal components. Statistical analysis shows a shift toward greater phasic activity during bed rest and follow up ( P < 0.001) with a significant interaction across muscles ( P < 0.001) specifically affecting the short lumbar extensors. These changes appear unrelated to skill acquisition over time ( P all ≥0.196). This change of a shift from tonic LP muscle activation to phasic is in line with prior research on the effects of reduced weight bearing on motor control.
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Trappe, Scott, Andrew Creer, Dustin Slivka, Kiril Minchev et Todd Trappe. « Single muscle fiber function with concurrent exercise or nutrition countermeasures during 60 days of bed rest in women ». Journal of Applied Physiology 103, no 4 (octobre 2007) : 1242–50. http://dx.doi.org/10.1152/japplphysiol.00560.2007.
Texte intégralRésumé :
There is limited information on skeletal muscle properties in women with unloading and countermeasure programs to protect the unloading-induced atrophy. The current investigation tested the hypothesis that a concurrent aerobic and resistance exercise training program would preserve size and contractile function of slow- and fast-twitch muscle fibers. A secondary objective was to test the hypothesis that a leucine-enriched high-protein diet would partially attenuate single fiber characteristics. Vastus lateralis muscle biopsies were obtained before and on day 59 of bed rest from a control (BR; n = 8), nutrition (BRN; n = 8), or exercise (BRE; n = 8) group. Single muscle fibers were studied for diameter, peak force (Po), contractile velocity, and power. Those in the BR group had a decrease ( P < 0.05) in myosin heavy chain (MHC) I diameter (−14%), Po (−35%), and power (−42%) and MHC IIa diameter (−16%) and Po (−31%; P = 0.06) and an increase ( P < 0.05) in MHC hybrid fibers. Changes in size and function of MHC I (−19 to −44%) and IIa (−21% to −30%) fibers and MHC distribution in BRN individuals were similar to results in the BR group. In BRE conditions, MHC I and IIa size and contractile function were preserved during bed rest. These data show that the concurrent exercise program preserved the myocellular profile of the vastus lateralis muscle during 60-day bed rest. To combat muscle atrophy and function with long-term unloading, the exercise prescription program used in this study should be considered as a viable training program for the upper leg muscles, whereas the nutritional intervention used cannot be recommended as a countermeasure for skeletal muscle.
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Trevino, Michelle B., Xiaolei Zhang, Robert A. Standley, Miao Wang, Xianlin Han, Felipe C. G. Reis, Muthu Periasamy et al. « Loss of mitochondrial energetics is associated with poor recovery of muscle function but not mass following disuse atrophy ». American Journal of Physiology-Endocrinology and Metabolism 317, no 5 (1 novembre 2019) : E899—E910. http://dx.doi.org/10.1152/ajpendo.00161.2019.
Texte intégralRésumé :
Skeletal muscle atrophy is a clinically important outcome of disuse because of injury, immobilization, or bed rest. Disuse atrophy is accompanied by mitochondrial dysfunction, which likely contributes to activation of the muscle atrophy program. However, the linkage of muscle mass and mitochondrial energetics during disuse atrophy and its recovery is incompletely understood. Transcriptomic analysis of muscle biopsies from healthy older adults subject to complete bed rest revealed marked inhibition of mitochondrial energy metabolic pathways. To determine the temporal sequence of muscle atrophy and changes in intramyocellular lipid and mitochondrial energetics, we conducted a time course of hind limb unloading-induced atrophy in adult mice. Mitochondrial respiration and calcium retention capacity were diminished, whereas H2O2 emission was increased within 3 days of unloading before significant muscle atrophy. These changes were associated with a decrease in total cardiolipin and profound changes in remodeled cardiolipin species. Hind limb unloading performed in muscle-specific peroxisome proliferator-activated receptor-γ coactivator-1α/β knockout mice, a model of mitochondrial dysfunction, did not affect muscle atrophy but impacted muscle function. These data suggest early mitochondrial remodeling affects muscle function but not mass during disuse atrophy. Early alterations in mitochondrial energetics and lipid remodeling may represent novel targets to prevent muscle functional impairment caused by disuse and to enhance recovery from periods of muscle atrophy.
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Berg, H. E., L. Larsson et P. A. Tesch. « Lower limb skeletal muscle function after 6 wk of bed rest ». Journal of Applied Physiology 82, no 1 (1 janvier 1997) : 182–88. http://dx.doi.org/10.1152/jappl.1997.82.1.182.
Texte intégralRésumé :
Berg, H. E., L. Larsson, and P. A. Tesch. Lower limb skeletal muscle function after 6 wk of bed rest. J. Appl. Physiol. 82(1): 182–188, 1997.—Force, electromyographic (EMG) activity, muscle mass, and fiber characteristics were studied in seven healthy men before and after 6 wk of bed rest. Maximum voluntary isometric and concentric knee extensor torque decreased ( P < 0.05) uniformly across angular velocities by 25–30% after bed rest. Maximum quadricep rectified EMG decreased by 19 ± 23%, whereas submaximum (100-Nm isometric action) EMG increased by 44 ± 28%. Knee extensor muscle cross-sectional area (CSA), assessed by using magnetic resonance imaging, decreased by 14 ± 4%. Maximum torque per knee extensor CSA decreased by 13 ± 9%. Vastus lateralis fiber CSA decreased 18 ± 14%. Neither type I, IIA, and IIB fiber percentages nor their relative proportions of myosin heavy chain (MHC) isoforms were altered after bed rest. Because the decline in strength could not be entirely accounted for by decreased muscle CSA, it is suggested that the strength loss is also due to factors resulting in decreased neural input to muscle and/or reduced specific tension of muscle, as evidenced by a decreased torque/EMG ratio. Additionally, it is concluded that muscle unloading in humans does not induce important changes in fiber type or MHC composition or in vivo muscle contractile properties.
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Ferrando, A. A., H. W. Lane, C. A. Stuart, J. Davis-Street et R. R. Wolfe. « Prolonged bed rest decreases skeletal muscle and whole body protein synthesis ». American Journal of Physiology-Endocrinology and Metabolism 270, no 4 (1 avril 1996) : E627—E633. http://dx.doi.org/10.1152/ajpendo.1996.270.4.e627.
Texte intégralRésumé :
We sought to determine the extent to which the loss of lean body mass and nitrogen during inactivity was due to alterations in skeletal muscle protein metabolism. Six male subjects were studied during 7 days of diet stabilization and after 14 days of stimulated microgravity (-6 degrees bed rest). Nitrogen balance became more negative (P < 0.03) during the 2nd wk of bed rest. Leg and whole body lean mass decreased after bed rest (P < 0.05). Serum cortisol, insulin, insulin-like growth factor I, and testosterone values did not change. Arteriovenous model calculations based on the infusion of L-[ring-13C6]-phenylalanine in five subjects revealed a 50% decrease in muscle protein synthesis (PS; P < 0.03). Fractional PS by tracer incorporation into muscle protein also decreased by 46% (P < 0.05). The decrease in PS was related to a corresponding decrease in the sum of intracellular amino acid appearance from protein breakdown and inward transport. Whole body protein synthesis determined by [15N]alanine ingestion on six subjects also revealed a 14% decrease (P < 0.01). Neither model-derived nor whole body values for protein breakdown change significantly. These results indicate that the loss of body protein with inactivity is predominantly due to a decrease in muscle PS and that this decrease is reflected in both whole body and skeletal muscle measures.
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Moffitt, Julia A., Angela J. Grippo, Terry G. Beltz et Alan Kim Johnson. « Hindlimb unloading elicits anhedonia and sympathovagal imbalance ». Journal of Applied Physiology 105, no 4 (octobre 2008) : 1049–59. http://dx.doi.org/10.1152/japplphysiol.90535.2008.
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The hindlimb-unloaded (HU) rat model elicits cardiovascular deconditioning and simulates the physiological adaptations to microgravity or prolonged bed rest in humans. Although psychological deficits have been documented following bed rest and spaceflight in humans, few studies have explored the psychological effects of cardiovascular deconditioning in animal models. Given the bidirectional link established between cardiac autonomic imbalance and psychological depression in both humans and in animal models, we hypothesized that hindlimb unloading would elicit an alteration in sympathovagal tone and behavioral indexes of psychological depression. Male, Sprague-Dawley rats confined to 14 days of HU displayed anhedonia (a core feature of human depression) compared with casted control (CC) animals evidenced by reduced sucrose preference (CC: 81 ± 2.9% baseline vs. HU: 58 ± 4.5% baseline) and reduced (rightward shift) operant responding for rewarding electrical brain stimulation (CC: 4.4 ± 0.3 μA vs. 7.3 ± 1.0 μA). Cardiac autonomic blockade revealed elevated sympathetic [CC: −54 ± 14.1 change in (Δ) beats/min vs. HU: −118 ± 7.6 Δ beats/min] and reduced parasympathetic (CC: 45 ± 11.8 Δ beats/min vs. HU: 8 ± 7.3 Δ beats/min) cardiac tone in HU rats. Heart rate variability was reduced (CC: 10 ± 1.4 ms vs. HU: 7 ± 0.7 ms), and spectral analysis of blood pressure indicated loss of total, low-, and high-frequency power, consistent with attenuated baroreflex function. These data indicate that cardiovascular deconditioning results in sympathovagal imbalance and behavioral signs consistent with psychological depression. These findings further elucidate the pathophysiological link between cardiovascular diseases and affective disorders.
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Zachwieja, Jeffrey J., Steven R. Smith, Jennifer C. Lovejoy, Jennifer C. Rood, Marlene M. Windhauser et George A. Bray. « Testosterone Administration Preserves Protein Balance But Not Muscle Strength during 28 Days of Bed Rest1 ». Journal of Clinical Endocrinology & ; Metabolism 84, no 1 (1 janvier 1999) : 207–12. http://dx.doi.org/10.1210/jcem.84.1.5420.
Texte intégralRésumé :
Decrements in muscle strength as a result of prolonged bed rest are well defined, but little is known about potential countermeasures for preventing loss of strength under this condition. The purpose of this study was to determine whether testosterone administration would preserve protein balance and muscle strength during prolonged bed rest. Ten healthy men (age, 36 ± 2 yr; height, 177.2 ± 3.4 cm; weight, 80.5 ± 3.9 kg; mean ± se) were admitted to our in-patient metabolic unit. After a 1-week ambulatory run-in period, each subject was confined to bed for 28 days at 6° head-down tilt while receiving a daily oral dose of T3 (50 μg/day). During the bed rest/T3 period, six of the men were randomized to receive testosterone enanthate by im injection (T; 200 mg/week) while four received placebo in a double blind fashion. Nitrogen balance was determined throughout, and whole body[ 13C]leucine kinetics were assessed at baseline and on day 26 of bed rest. Before bed rest and on the third day of reambulation, the muscle strength of the knee extensors and flexors and shoulder extensors and flexors was determined at 60°/s on a Cybex isokinetic dynamometer. Despite improved [13C]leucine kinetics and maintenance of nitrogen balance and lean body mass in T-treated subjects, little preservation of muscle strength, particularly in the knee extensors, was noted. Muscle strength[ reported as the best work repetition in foot-pounds (FtLb)] for right knee extensors declined (P = 0.011) similarly in both groups; from 165 ± 15 to 126 ± 18 FtLb in T-treated men and from 179 ± 22 to 149 ± 13 FtLb in placebo-treated men. Overall, there was less of a decline in extension and flexion strength of the shoulder compared to the knee, with no benefit from T. These results suggest that in the absence of daily ambulatory activity, T administration will not increase or, in the case of this bed rest model, preserve muscle strength.
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D’Amuri, Andrea, Juana Maria Sanz, Stefano Lazzer, Rado Pišot, Bostjan Šimunič, Gianni Biolo, Giovanni Zuliani et al. « Irisin Attenuates Muscle Impairment during Bed Rest through Muscle-Adipose Tissue Crosstalk ». Biology 11, no 7 (30 juin 2022) : 999. http://dx.doi.org/10.3390/biology11070999.
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The detrimental effect of physical inactivity on muscle characteristics are well known. Irisin, an exercise-induced myokine cleaved from membrane protein fibronectin type III domain-containing protein-5 (FNDC5), mediates at least partially the metabolic benefits of exercise. This study aimed to assess the interplay between prolonged inactivity, circulating irisin, muscle performance, muscle fibers characteristics, as well as the FNDC5 gene expression (FNDC5ge) in muscle and adipose tissue among healthy subjects. Twenty-three healthy volunteers were tested before and after 14 days of Bed Rest, (BR). Post-BR circulating levels of irisin significantly increased, whereas body composition, muscle performance, and muscle fiber characteristics deteriorated. Among the subjects achieving the highest post-BR increase of irisin, the lowest reduction in maximal voluntary contraction and specific force of Fiber Slow/1, the highest increase of FNDC5ge in adipose tissue, and no variation of FNDC5ge in skeletal muscle were recorded. Subjects who had the highest FNDC5ge in adipose tissue but not in muscle tissue showed the highest circulating irisin levels and could better withstand the harmful effect of BR.
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Belavý, Daniel L., Gabriele Armbrecht, Ulf Gast, Carolyn A. Richardson, Julie A. Hides et Dieter Felsenberg. « Countermeasures against lumbar spine deconditioning in prolonged bed rest : resistive exercise with and without whole body vibration ». Journal of Applied Physiology 109, no 6 (décembre 2010) : 1801–11. http://dx.doi.org/10.1152/japplphysiol.00707.2010.
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To evaluate the effect of short-duration, high-load resistive exercise, with and without whole body vibration on lumbar muscle size, intervertebral disk and spinal morphology changes, and low back pain (LBP) incidence during prolonged bed rest, 24 subjects underwent 60 days of head-down tilt bed rest and performed either resistive vibration exercise ( n = 7), resistive exercise only ( n = 8), or no exercise ( n = 9; 2nd Berlin Bed-Rest Study). Discal and spinal shape was measured from sagittal plane magnetic resonance images. Cross-sectional areas (CSAs) of the multifidus, erector spinae, quadratus lumborum, and psoas were measured on para-axial magnetic resonance images. LBP incidence was assessed with questionnaires at regular intervals. The countermeasures reduced CSA loss in the multifidus, lumbar erector spinae and quadratus lumborum muscles, with greater increases in psoas muscle CSA seen in the countermeasure groups ( P ≤ 0.004). There was little statistical evidence for an additional effect of whole body vibration above resistive exercise alone on these muscle changes. Exercise subjects reported LBP more frequently in the first week of bed rest, but this was only significant in resistive exercise only ( P = 0.011 vs. control, resistive vibration exercise vs. control: P = 0.56). No effect of the countermeasures on changes in spinal morphology was seen ( P ≥ 0.22). The results suggest that high-load resistive exercise, with or without whole body vibration, performed 3 days/wk can reduce lumbar muscle atrophy, but further countermeasure optimization is required.
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Arentson-Lantz, Emily J., Kirk L. English, Douglas Paddon-Jones et Christopher S. Fry. « Fourteen days of bed rest induces a decline in satellite cell content and robust atrophy of skeletal muscle fibers in middle-aged adults ». Journal of Applied Physiology 120, no 8 (15 avril 2016) : 965–75. http://dx.doi.org/10.1152/japplphysiol.00799.2015.
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Bed rest, a ground-based spaceflight analog, induces robust atrophy of skeletal muscle, an effect that is exacerbated with increasing age. We examined the effect of 14 days of bed rest on skeletal muscle satellite cell content and fiber type atrophy in middle-aged adults, an understudied age demographic with few overt signs of muscle aging that is representative of astronauts who perform long-duration spaceflight. Muscle biopsies were obtained from the vastus lateralis of healthy middle-aged adults [ n = 7 (4 male, 3 female); age: 51 ± 1 yr] before (Pre-BR) and after (Post-BR) 14 days of bed rest. Immunohistochemical analyses were used to quantify myosin heavy chain (MyHC) isoform expression, cross-sectional area (CSA), satellite cell and myonuclear content, and capillary density. Peak oxygen consumption, knee extensor strength, and body composition were also measured Pre-BR and Post-BR. Post-BR MyHC type 2a fiber percentage was reduced, and mean CSA decreased in all fiber types (−24 ± 5%; P < 0.05). Satellite cell content was also reduced Post-BR (−39 ± 9%; P < 0.05), and the change in satellite cell content was significantly correlated with the change in mean fiber CSA ( r2 = 0.60; P < 0.05). A decline in capillary density was observed Post-BR (−23 ± 6%; P < 0.05), and Post-BR capillary content was significantly associated with Post-BR peak aerobic capacity ( r2 = 0.59; P < 0.05). A subtle decline in myonuclear content occurred during bed rest (−5 ± 1%; P < 0.05). The rapid maladaptation of skeletal muscle to 14 days of mechanical unloading in middle-aged adults emphasizes the need for robust countermeasures to preserve muscle function in astronauts.
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Mutin-Carnino, M., A. Carnino, S. Roffino et A. Chopard. « Effect of Muscle Unloading, Reloading and Exercise on Inflammation during a Head-down Bed Rest ». International Journal of Sports Medicine 35, no 01 (3 juillet 2013) : 28–34. http://dx.doi.org/10.1055/s-0033-1343407.
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Dyckman, Damian J., Charity L. Sauder et Chester A. Ray. « Effects of short-term and prolonged bed rest on the vestibulosympathetic reflex ». American Journal of Physiology-Heart and Circulatory Physiology 302, no 1 (janvier 2012) : H368—H374. http://dx.doi.org/10.1152/ajpheart.00193.2011.
Texte intégralRésumé :
The mechanism(s) for post-bed rest (BR) orthostatic intolerance is equivocal. The vestibulosympathetic reflex contributes to postural blood pressure regulation. It was hypothesized that muscle sympathetic nerve responses to otolith stimulation would be attenuated by prolonged head-down BR. Arterial blood pressure, heart rate, muscle sympathetic nerve activity (MSNA), and peripheral vascular conductance were measured during head-down rotation (HDR; otolith organ stimulation) in the prone posture before and after short-duration (24 h; n = 22) and prolonged (36 ± 1 day; n = 8) BR. Head-up tilt at 80° was performed to assess orthostatic tolerance. After short-duration BR, MSNA responses to HDR were preserved (Δ5 ± 1 bursts/min, Δ53 ± 13% burst frequency, Δ65 ± 13% total activity; P < 0.001). After prolonged BR, MSNA responses to HDR were attenuated ∼50%. MSNA increased by Δ8 ± 2 vs. Δ3 ± 2 bursts/min and Δ83 ± 12 vs. Δ34 ± 22% total activity during HDR before and after prolonged BR, respectively. Moreover, these results were observed in three subjects tested again after 75 ± 1 days of BR. This reduction in MSNA responses to otolith organ stimulation at 5 wk occurred with reductions in head-up tilt duration. These results indicate that prolonged BR (∼5 wk) unlike short-term BR (24 h) attenuates the vestibulosympathetic reflex and possibly contributes to orthostatic intolerance following BR in humans. These results suggest a novel mechanism in the development of orthostatic intolerance in humans.
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Ahuja, Maninder. « Bed Rest in Pregnancy and Its Related Complications : Is It Needed ? » Journal of South Asian Federation of Obstetrics and Gynaecology 4, no 3 (2012) : 147–50. http://dx.doi.org/10.5005/jp-journals-10006-1199.
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ABSTRACT For centuries it is common myth to advice bed rest during pregnancy. At the least pretext bed rest is advised by family members and by health care providers also. But review of literature and RCT shows that in reality bed rest does not alter the course of pregnancy in various complications. Role of bed rest has been examined in singleton, twin and triplet pregnancies but was not found useful. Prolonged bed rest is rather harmful as it causes increased calcium excretion, loss of muscle mass, financial loss and increased psychological rest for the pregnant woman and her family. Moderate exercise is advisable throughout pregnancy to maintain tone of muscles and range of movements. So till we have more proof we should be cautious in advising pregnant patients about bed rest. It can be limited activity where we feel it is not advisable to overexert her. How to cite this article Ahuja M. Bed Rest in Pregnancy and Its Related Complications: Is It Needed?. J South Asian Feder Obst Gynae 2012;4(3):147-150.
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Fitts, R. H., J. G. Romatowski, J. R. Peters, D. Paddon-Jones, R. R. Wolfe et A. A. Ferrando. « The deleterious effects of bed rest on human skeletal muscle fibers are exacerbated by hypercortisolemia and ameliorated by dietary supplementation ». American Journal of Physiology-Cell Physiology 293, no 1 (juillet 2007) : C313—C320. http://dx.doi.org/10.1152/ajpcell.00573.2006.
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Prolonged inactivity associated with bed rest in a clinical setting or spaceflight is frequently associated with hypercortisolemia and inadequate caloric intake. Here, we determined the effect of 28 days of bed rest (BR); bed rest plus hypercortisolemia (BRHC); and bed rest plus essential amino acid (AA) and carbohydrate (CHO) supplement (BRAA) on the size and function of single slow- and fast-twitch muscle fibers. Supplementing meals, the BRAA group consumed 16.5 g essential amino acids and 30 g sucrose at 1100, 1600, and 2100 h, and the BRHC subjects received 5 daily doses of 10–15 mg of oral hydrocortisone sodium succinate throughout bed rest. Bed rest induced atrophy and loss of force (mN) and power (μN·FL·s−1) in single fibers was exacerbated by hypercortisolemia where soleus peak force declined by 23% in the type I fiber from a prevalue of 0.78 ± 0.02 to 0.60 ± 0.02 mN post bed rest (compared to a 7% decline with bed rest alone) and 27% in the type II fiber (1.10 ± 0.08 vs. 0.81 ± 0.05 mN). In the BRHC group, peak power dropped by 19, 15, and 11% in the soleus type I, and vastus lateralis (VL) type I and II fibers, respectively. The AA/CHO supplement protected against the bed rest-induced loss of peak force in the type I soleus and peak power in the VL type II fibers. These results provide evidence that an AA/CHO supplement might serve as a successful countermeasure to help preserve muscle function during periods of relative inactivity.
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Montmerle, Stéphanie, Jonas Spaak et Dag Linnarsson. « Lung function during and after prolonged head-down bed rest ». Journal of Applied Physiology 92, no 1 (1 janvier 2002) : 75–83. http://dx.doi.org/10.1152/jappl.2002.92.1.75.
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We determined the effects of prolonged head-down tilt bed rest (HDT) on lung mechanics and gas exchange. Six subjects were studied in supine and upright postures before (control), during [ day 113(D113)], and after (R + number of days of recovery) 120 days of HDT. Peak expiratory flow (PF) never differed between positions at any time and never differed from controls. Maximal midexpiratory flow (FEF25–75%) was lower in the supine than in the upright posture before HDT and was reduced in the supine posture by about 20% between baseline and D113, R + 0, and R + 3. The diffusing capacity for carbon monoxide corrected to a standardized alveolar volume (volume-corrected Dl CO) was lower in the upright than in the supine posture and decreased in both postures by 20% between baseline and R + 0 and by 15% between baseline and R + 15. Pulmonary blood flow (Q˙C) increased from R + 0 to R + 3 by 20 (supine) and 35% (upright). As PF is mostly effort dependent, our data speak against major respiratory muscle deconditioning after 120 days of HDT. The decrease in FEF25–75% suggests a reduction in elastic recoil. Time courses of volume-corrected Dl CO andQ˙C could be explained by a decrease in central blood volume during and immediately after HDT.
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Manganotti, Paolo, Alex Buoite Stella, Milos Ajcevic, Filippo Giorgio di Girolamo, Gianni Biolo, Martino V. Franchi, Elena Monti et al. « Peripheral nerve adaptations to 10 days of horizontal bed rest in healthy young adult males ». American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 321, no 3 (1 septembre 2021) : R495—R503. http://dx.doi.org/10.1152/ajpregu.00146.2021.
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Space analogs, such as bed rest, are used to reproduce microgravity-induced morphological and physiological changes and can be used as clinical models of prolonged inactivity. Nevertheless, nonuniform decreases in muscle mass and function have been frequently reported, and peripheral nerve adaptations have been poorly studied, although some of these mechanisms may be explained. Ten young healthy males (18–33 yr) underwent 10 days of horizontal bed rest. Peripheral neurophysiological assessments were performed bilaterally for the dominant (DL) and nondominant upper and lower limbs (N-DL) on the 1st and 10th day of bed rest, including ultrasound of the median, deep peroneal nerve (DPN), and common fibular nerve (CFN) , as well as a complete nerve conduction study (NCS) of the upper and lower limbs. Consistently, reduced F waves, suggesting peripheral nerve dysfunction, of both the peroneal (DL: P = 0.005, N-DL: P = 0.013) and tibial nerves (DL: P = 0.037, N-DL: P = 0.005) were found bilaterally, whereas no changes were observed in nerve ultrasound or other parameters of the NCS of both the upper and lower limbs. In these young healthy males, only the F waves, known to respond to postural changes, were significantly affected by short-term bed rest. These preliminary results suggest that during simulated microgravity, most changes occur at the muscle or central nervous system level. Since the assessment of F waves is common in clinical neurophysiological examinations, caution should be used when testing individuals after prolonged immobility.
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Baker, Steven, Melinda Gilhen-Baker et Giovanni N. Roviello. « The Role of Nutrition and Forest-Bathing in the Physical Rehabilitation of Physically Inactive Patients : From the Molecular Aspects to New Nature-Inspired Techniques ». International Journal of Environmental Research and Public Health 20, no 1 (31 décembre 2022) : 793. http://dx.doi.org/10.3390/ijerph20010793.
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Physical rehabilitation plays a fundamental role in the management of individuals with disabilities associated with age-related muscle loss or affected by catastrophic conditions such as trauma, surgery, cancer or other severe pathologies. These events have in common an extended period of physical inactivity. Patients who undergo prolonged bed rest often present with a number of complications; for example, muscle loss that can exacerbate existing conditions determined by sarcopenia, which in turn greatly limits physical functions. The main scope of this work is to summarize certain key strategies for the physiotherapeutic management of physically inactive patients, regardless of the reason behind their prolonged bed rest, with a particular focus on physical rehabilitation, nutrition and forest-bathing. The importance of correct nutrition in counter-acting the loss of muscle mass and consequent function is explored alongside a description of the main nutrients that are needed for muscle regeneration. From a biomolecular perspective, some specific molecular mechanisms associated with physical rehabilitation are also reported not only in the context of physical therapy, but also within nature-inspired techniques, such as forest-bathing as well as body self-healing. Combining a targeted physiotherapeutic approach with an appropriate diet as well as nature-based therapy could thus help with the recovery of bed ridden patients.
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Trappe, Scott W., Todd A. Trappe, Gary A. Lee, Jeffery J. Widrick, David L. Costill et Robert H. Fitts. « Comparison of a space shuttle flight (STS-78) and bed rest on human muscle function ». Journal of Applied Physiology 91, no 1 (1 juillet 2001) : 57–64. http://dx.doi.org/10.1152/jappl.2001.91.1.57.
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The purpose of this investigation was to assess muscle fiber size, composition, and in vivo contractile characteristics of the calf muscle of four male crew members during a 17-day spaceflight (SF; Life and Microgravity Sciences Spacelab Shuttle Transport System-78 mission) and eight men during a 17-day bed rest (BR). The protocols and timelines of these two investigations were identical, therefore allowing for direct comparisons between SF and the BR. The subjects' age, height, and weight were 43 ± 2 yr, 183 ± 4 cm, and 86 ± 3 kg for SF and 43 ± 2 yr, 182 ± 3 cm, and 82 ± 4 kg for BR, respectively. Calf muscle strength was examined before SF and BR; on days 2, 8, and 12 during SF and BR; and on days 2 and 8 of recovery. Muscle biopsies were obtained before and within 3 h after SF (gastrocnemius and soleus) and BR (soleus) before reloading. Maximal isometric calf strength and the force-velocity characteristics were unchanged with SF or BR. Additionally, neither SF nor BR had any effect on fiber composition or fiber size of the calf muscles studied. In summary, no changes in calf muscle strength and morphology were observed after the 17-day SF and BR. Because muscle strength is lost during unloading, both during spaceflight and on the ground, these data suggest that the testing sequence employed during the SF and BR may have served as a resistance training countermeasure to attenuate whole muscle strength loss.
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Kwon, Oh Sung, Ruth E. Tanner, Katherine M. Barrows, Marah Runtsch, J. David Symons, Thunder Jalili, Benjamin T. Bikman, Donald A. McClain, Ryan M. O'Connell et Micah J. Drummond. « MyD88 regulates physical inactivity-induced skeletal muscle inflammation, ceramide biosynthesis signaling, and glucose intolerance ». American Journal of Physiology-Endocrinology and Metabolism 309, no 1 (1 juillet 2015) : E11—E21. http://dx.doi.org/10.1152/ajpendo.00124.2015.
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Physical inactivity in older adults is a risk factor for developing glucose intolerance and impaired skeletal muscle function. Elevated inflammation and ceramide biosynthesis have been implicated in metabolic disruption and are linked to Toll-like receptor (TLR)/myeloid differentiation primary response 88 (MyD88) signaling. We hypothesize that a physical inactivity stimulus, capable of inducing glucose intolerance, would increase skeletal muscle inflammation and ceramide biosynthesis signaling and that this response would be regulated by the TLR/MyD88 pathway. Therefore, we subjected wild-type (WT) and MyD88−/− mice to hindlimb unloading (HU) for 14 days or an ambulatory control period. We observed impaired glucose uptake, muscle insulin signaling (p-Akt), and increased markers of NF-κB signaling (p-IκBα), inflammation (p-JNK, IL-6), TLR4, and the rate-limiting enzyme of ceramide biosynthesis, SPT2, with HU WT ( P < 0.05), but not in HU MyD88−/− mice. Concurrently, we found that 5 days of bed rest in older adults resulted in whole body glucose dysregulation, impaired skeletal muscle insulin signaling, and upregulation of muscle IL-6 and SPT2 ( P < 0.05). Post-bed rest TLR4 abundance was tightly correlated with impaired postprandial insulin and glucose levels. In conclusion, MyD88 signaling is necessary for the increased inflammation, ceramide biosynthesis signaling, and compromised metabolic function that accompanies physical inactivity.
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Ferrando, A. A., K. D. Tipton, M. M. Bamman et R. R. Wolfe. « RESISTANCE EXERCISE PREVENTS THE DECREASE OF MUSCLE PROTEIN SYNTHESIS DURING PROLONGED BED REST 776 ». Medicine & Science in Sports & Exercise 28, Supplement (mai 1996) : 130. http://dx.doi.org/10.1097/00005768-199605001-00774.
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Ferretti, G. « The Effect of Prolonged Bed Rest on Maximal Instantaneous Muscle Power and its Determinants ». International Journal of Sports Medicine 18, S 4 (octobre 1997) : S287—S289. http://dx.doi.org/10.1055/s-2007-972728.
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Tousen, Yuko, Ryota Ichimaru, Takashi Kondo, Masaki Inada, Chisato Miyaura et Yoshiko Ishimi. « The Combination of Soy Isoflavones and Resveratrol Preserve Bone Mineral Density in Hindlimb-Unloaded Mice ». Nutrients 12, no 7 (9 juillet 2020) : 2043. http://dx.doi.org/10.3390/nu12072043.
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It is well known that physical inactivity during space flight or prolonged bed rest causes rapid bone loss. Soy isoflavones (ISOs) and resveratrol (RES) have been reported to be useful to maintain a positive balance for bone turnover. Therefore, we examined the combined effects of ISO and RES on bone loss that was induced by hindlimb-unloading in mice. Female eight-week-old ddY mice were divided into the following six groups (n = 6–8 each): normally housed mice, loading mice, hindlimb-unloading (UL) mice fed a control diet, UL mice fed a 0.16% ISO conjugates, UL mice fed a 0.15% RES diet, and UL mice fed a 0.16% ISO and 0.15% RES diet. After three weeks, femoral bone mineral density was markedly decreased in unloading mice. The combination of ISO and RES prevented bone loss and especially maintained the trabecular bone mineral density more effectively compared with cortical bones. ISO and/or RES inhibited the increase in the RANKL/OPG expression ratio in bone marrow cells in UL mice. These results suggest that the combination of ISO and RES had a preventive effect against bone loss induced by hindlimb-unloading in mice. These osteoprotective effects of ISO and RES may result from the inhibition of bone resorption.
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Perhonen, Merja A., Fatima Franco, Lynda D. Lane, Jay C. Buckey, C. Gunnar Blomqvist, Joseph E. Zerwekh, Ronald M. Peshock, Paul T. Weatherall et Benjamin D. Levine. « Cardiac atrophy after bed rest and spaceflight ». Journal of Applied Physiology 91, no 2 (1 août 2001) : 645–53. http://dx.doi.org/10.1152/jappl.2001.91.2.645.
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Cardiac muscle adapts well to changes in loading conditions. For example, left ventricular (LV) hypertrophy may be induced physiologically (via exercise training) or pathologically (via hypertension or valvular heart disease). If hypertension is treated, LV hypertrophy regresses, suggesting a sensitivity to LV work. However, whether physical inactivity in nonathletic populations causes adaptive changes in LV mass or even frank atrophy is not clear. We exposed previously sedentary men to 6 ( n = 5) and 12 ( n = 3) wk of horizontal bed rest. LV and right ventricular (RV) mass and end-diastolic volume were measured using cine magnetic resonance imaging (MRI) at 2, 6, and 12 wk of bed rest; five healthy men were also studied before and after at least 6 wk of routine daily activities as controls. In addition, four astronauts were exposed to the complete elimination of hydrostatic gradients during a spaceflight of 10 days. During bed rest, LV mass decreased by 8.0 ± 2.2% ( P = 0.005) after 6 wk with an additional atrophy of 7.6 ± 2.3% in the subjects who remained in bed for 12 wk; there was no change in LV mass for the control subjects (153.0 ± 12.2 vs. 153.4 ± 12.1 g, P = 0.81). Mean wall thickness decreased (4 ± 2.5%, P = 0.01) after 6 wk of bed rest associated with the decrease in LV mass, suggesting a physiological remodeling with respect to altered load. LV end-diastolic volume decreased by 14 ± 1.7% ( P = 0.002) after 2 wk of bed rest and changed minimally thereafter. After 6 wk of bed rest, RV free wall mass decreased by 10 ± 2.7% ( P = 0.06) and RV end-diastolic volume by 16 ± 7.9% ( P = 0.06). After spaceflight, LV mass decreased by 12 ± 6.9% ( P = 0.07). In conclusion, cardiac atrophy occurs during prolonged (6 wk) horizontal bed rest and may also occur after short-term spaceflight. We suggest that cardiac atrophy is due to a physiological adaptation to reduced myocardial load and work in real or simulated microgravity and demonstrates the plasticity of cardiac muscle under different loading conditions.
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Berg, H. E., G. A. Dudley, T. Haggmark, H. Ohlsen et P. A. Tesch. « Effects of lower limb unloading on skeletal muscle mass and function in humans ». Journal of Applied Physiology 70, no 4 (1 avril 1991) : 1882–85. http://dx.doi.org/10.1152/jappl.1991.70.4.1882.
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A model to simulate effects of microgravity on skeletal muscle mass and function in humans has been developed. Unilateral lower limb unloading that allowed ankle, knee, and hip joint mobility was conducted in six healthy men by suspending one lower limb and having the subjects walk on crutches. They performed maximal unilateral concentric or eccentric quadriceps actions at different angular velocities before and after 4 wk of suspension and after 4 days and after 7 wk of uncontrolled recovery. Peak torque (PT) and angle-specific torque (AST) were measured. Muscle cross-sectional area (CSA) and radiological density (RD) of the thigh were assessed by means of computerized tomography. Concentric and eccentric PT and AST across speeds decreased (P less than 0.05) by 22 and 16%, respectively, in response to unloading. At 4 days of recovery PT (-11%) and AST (-7%) were still lower (P less than 0.05) than before. Muscle CSA and RD decreased (P less than 0.05) by 7 and 6%, respectively. After 7 wk of recovery PT, AST, CSA, and RD had returned to normal. The control limb showed no changes over the experimental period except for a 6% decrease (P less than 0.05) in RD. It is suggested that this human model of unloading could serve to simulate effects of microgravity on skeletal muscle mass and function because reductions in muscle mass and strength were of similar magnitude to those produced by bed rest.
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FERRANDO, ARNY A., CHARLES A. STUART, MELINDA SHEFFIELD-MOORE et ROBERT R. WOLFE. « Inactivity Amplifies the Catabolic Response of Skeletal Muscle to Cortisol* ». Journal of Clinical Endocrinology & ; Metabolism 84, no 10 (1 octobre 1999) : 3515–21. http://dx.doi.org/10.1210/jcem.84.10.6046.
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Abstract Severe injury or trauma is accompanied by both hypercortisolemia and prolonged inactivity or bed rest (BR). Trauma and BR alone each result in a loss of muscle nitrogen, albeit through different metabolic alterations. Although BR alone can result in a 2–3% loss of lean body mass, the effects of severe trauma can be 2- to 3-fold greater. We investigated the combined effects of hypercortisolemia and prolonged inactivity on muscle protein metabolism in healthy volunteers. Six males were studied before and after 14 days of strict BR using a model based on arteriovenous sampling and muscle biopsy. Fractional synthesis and breakdown rates of skeletal muscle protein were also directly calculated. Each assessment of protein metabolism was conducted during a 12-h infusion of hydrocortisone sodium succinate (120 μg/kg·h), resulting in blood cortisol concentrations that mimic severe injury (≈31 μg/dL). After 14 days of strict BR, hypercortisolemia increased phenylalanine efflux from muscle by 3-fold (P < 0.05). The augmented negative amino acid balance was the result of an increased muscle protein breakdown (P < 0.05) without a concomitant change in muscle protein synthesis. Muscle efflux of glutamine and alanine increased significantly after bed rest due to a significant increase in de novo synthesis (P < 0.05). Thus, inactivity sensitizes skeletal muscle to the catabolic effects of hypercortisolemia. Furthermore, these effects on healthy volunteers are analogous to those seen after severe injury.
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Belavý, Daniel L., Tanja Miokovic, Gabriele Armbrecht et Dieter Felsenberg. « Hypertrophy in the cervical muscles and thoracic discs in bed rest ? » Journal of Applied Physiology 115, no 5 (1 septembre 2013) : 586–96. http://dx.doi.org/10.1152/japplphysiol.00376.2013.
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The impact of prolonged bed rest on the cervical and upper thoracic spine is unknown. In the 2nd Berlin BedRest Study (BBR2-2), 24 male subjects underwent 60-day bed rest and performed either no exercise, resistive exercise, or resistive exercise with whole body vibration. Subjects were followed for 2 yr after bed rest. On axial cervical magnetic resonance images from the skull to T3, the volumes of the semispinalis capitis, splenius capitis, spinalis cervicis, longus capitis, longus colli, levator scapulae, sternocleidomastoid, middle and posterior scalenes, and anterior scalenes were measured. Disc height, anteroposterior width, and volume were measured from C2/3 to T6/7 on sagittal images. The volume of all muscles, with the exception of semispinalis capitis, increased during bed rest ( P < 0.025). There were no significant differences between the groups for changes in the muscles. Increased upper and midthoracic spine disc height and volume ( P < 0.001) was seen during bed rest, and disc height increases persisted at least 6 mo after bed rest. Increases in thoracic disc height were greater ( P = 0.003) in the resistive vibration exercise group than in control. On radiological review, two subjects showed new injuries to the mid-lower thoracic spine. One of these subjects reported a midthoracic pain incident during maximal strength testing before bed rest and the other after countermeasure exercise on day 3 of bed rest. We conclude that bed rest is associated with increased disc size in the thoracic region and increases in muscle volume at the neck. The exercise device needs to be modified to ensure that load is distributed in a more physiological fashion.
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Owen, Patrick J., Gabriele Armbrecht, Martin Bansmann, Jochen Zange, Regina Pohle-Fröhlich, Dieter Felsenberg et Daniel L. Belavý. « Whey protein supplementation with vibration exercise ameliorates lumbar paraspinal muscle atrophy in prolonged bed rest ». Journal of Applied Physiology 128, no 6 (1 juin 2020) : 1568–78. http://dx.doi.org/10.1152/japplphysiol.00125.2020.
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We examined the impact of adding protein supplementation to exercise (resistive vibration exercise) as a countermeasure against changes in the spine during spaceflight simulation. We found that adding the protein supplementation reduced spine muscle atrophy more than exercise alone. Neither countermeasure approach prevented changes in the disks in the spine or impacted back pain reports.
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Tousen, Yuko, Takashi Kondo, Tsuyoshi Chiba et Yoshiko Ishimi. « Green Tea Catechin, Epigallocatechin Gallate, Prevents Bone Loss in Hindlimb-Unloading Mice ». Current Developments in Nutrition 5, Supplement_2 (juin 2021) : 59. http://dx.doi.org/10.1093/cdn/nzab033_059.
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Abstract Objectives Osteoporosis is a major health problem in the elderly characterized by bone loss and micro-architectural deterioration of bone tissue and associated with an increased risk of fracture. Prolonged bed rest, or physical inactivity during space flight causes rapid and marked bone loss. The effects of catechin, the main ingredient of Japanese green tea, on the bone are currently under study. It has been shown that green tea catechin modulates bone resorption in osteoclasts. However, there is no evidence supporting its inhibitory effect on bone loss during physical inactivity. In the present study, we investigated whether green tea catechin prevented bone loss through skeletal hindlimb-unloading in mice. Methods Female 8-week-old ddY mice were divided into five groups (n = 6–8 each) and subjected to: (1) normal housing fed a control diet, (2) sham unloading fed a control diet, (3) hind limb-unloading fed a control diet, (4) hind limb-unloading fed a 0.05% epigallocatechin gallate (EGCG)-containing diet, and (5) hind limb-unloading fed a 0.25% EGCG-containing diet for three weeks. Purified EGCG (97%) was used for green tea catechin. Results Bone mineral density of the tibia significantly decreased in hind limb-unloading mice. Treatment with 0.25% EGCG prevented bone loss and maintained trabecular bone mineral density more significantly than in cortical bones. The 0.25% EGCG diet inhibited decrease in the gene expression of alkaline phosphatase, a marker of bone formation, in the bone marrow in hind limb-unloading mice. Conclusions These results suggest that EGCG has ability to prevent bone loss induced by hindlimb-unloading in mice. These osteoprotective effects of EGCG may result from the inhibition of unloading-induced decrease in bone formation. Funding Sources This work was supported by the Honjo International Scholarship Foundation of Japan.
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Khan, Md Shah Zaman, Abul Khair Ahmed Zaman et AKM Asad Ud Doza. « Physical Rehabilitation in the ICU ». Bangladesh Critical Care Journal 3, no 2 (22 septembre 2015) : 63–66. http://dx.doi.org/10.3329/bccj.v3i2.25113.
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Intensive care unit (ICU) based rehabilitation has become an important evidence-based component in the management of patients with critical illness. In addition to critical illness, prolonged bed rest and immobility may lead to severe physical deconditioning and loss of muscle mass and muscle weakness. Intensive care unit acquired weakness is associated with increased duration of mechanical ventilation and weaning, longer ICU and hospital stay, and increased mortality. These physical impairments may last for years after ICU discharge. Early Physical Medicine and Rehabilitation (PM&R) interventions in the ICU may attenuate or prevent the weakness and physical impairments occurring during critical illness. This article reviews the effects of prolong bed rest and inactivity, early PM&R interventions, their safety, feasibility, benefits and future directions for early PM&R in the ICU.Bangladesh Crit Care J September 2015; 3 (2): 63-66
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Pancheva, Marieta V., Vladimir S. Panchev et Adelina V. Suvandjieva. « Lower body negative pressure vs. lower body positive pressure to prevent cardiac atrophy after bed rest and spaceflight. What caused the controversy ? » Journal of Applied Physiology 100, no 3 (mars 2006) : 1090. http://dx.doi.org/10.1152/japplphysiol.00950.2005.
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Cardiac muscle adapts well to changes in loading conditions. For example, left ventricular (LV) hypertrophy may be induced physiologically (via exercise training) or pathologically (via hypertension or valvular heart disease). If hypertension is treated, LV hypertrophy regresses, suggesting a sensitivity to LV work. However, whether physical inactivity in nonathletic populations causes adaptive changes in LV mass or even frank atrophy is not clear. We exposed previously sedentary men to 6 ( n = 5) and 12 ( n = 3) wk of horizontal bed rest. LV and right ventricular (RV) mass and end-diastolic volume were measured using cine magnetic resonance imaging (MRI) at 2, 6, and 12 wk of bed rest; five healthy men were also studied before and after at least 6 wk of routine daily activities as controls. In addition, four astronauts were exposed to the complete elimination of hydrostatic gradients during a spaceflight of 10 days. During bed rest, LV mass decreased by 8.0 ± 2.2% ( P = 0.005) after 6 wk with an additional atrophy of 7.6 ± 2.3% in the subjects who remained in bed for 12 wk; there was no change in LV mass for the control subjects (153.0 ± 12.2 vs. 153.4 ± 12.1 g, P = 0.81). Mean wall thickness decreased (4 ± 2.5%, P = 0.01) after 6 wk of bed rest associated with the decrease in LV mass, suggesting a physiological remodeling with respect to altered load. LV end-diastolic volume decreased by 14 ± 1.7% ( P = 0.002) after 2 wk of bed rest and changed minimally thereafter. After 6 wk of bed rest, RV free wall mass decreased by 10 ± 2.7% ( P = 0.06) and RV end-diastolic volume by 16 ± 7.9% ( P = 0.06). After spaceflight, LV mass decreased by 12 ± 6.9% ( P = 0.07). In conclusion, cardiac atrophy occurs during prolonged (6 wk) horizontal bed rest and may also occur after short-term spaceflight. We suggest that cardiac atrophy is due to a physiological adaptation to reduced myocardial load and work in real or simulated microgravity and demonstrates the plasticity of cardiac muscle under different loading conditions.
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Dorfman, Todd A., Benjamin D. Levine, Tommy Tillery, Ronald M. Peshock, Jeff L. Hastings, Suzanne M. Schneider, Brandon R. Macias, Gianni Biolo et Alan R. Hargens. « Cardiac atrophy in women following bed rest ». Journal of Applied Physiology 103, no 1 (juillet 2007) : 8–16. http://dx.doi.org/10.1152/japplphysiol.01162.2006.
Texte intégralRésumé :
Both chronic microgravity exposure and long-duration bed rest induce cardiac atrophy, which leads to reduced standing stroke volume and orthostatic intolerance. However, despite the fact that women appear to be more susceptible to postspaceflight presyncope and orthostatic hypotension than male astronauts, most previous high-resolution studies of cardiac morphology following microgravity have been performed only in men. Because female athletes have less physiological hypertrophy than male athletes, we reasoned that they also might have altered physiological cardiac atrophy after bed rest. Magnetic resonance imaging was performed in 24 healthy young women (32.1 ± 4 yr) to measure left ventricular (LV) and right ventricular (RV) mass, volumes, and morphology accurately before and after 60 days of 6° head-down tilt (HDT) bed rest. Subjects were matched and then randomly assigned to sedentary bed rest (controls, n = 8) or two treatment groups consisting of 1) exercise training using supine treadmill running within lower body negative pressure plus resistive training ( n = 8), or 2) protein (0.45 g·kg−1·day−1 increase) plus branched-chain amino acid (BCAA) (7.2 g/day) supplementation ( n = 8). After sedentary bed rest without nutritional supplementation, there were significant reductions in LV (96 ± 26 to 77 ± 25 ml; P = 0.03) and RV volumes (104 ± 33 to 86 ± 25 ml; P = 0.02), LV (2.2 ± 0.2 to 2.0 ± 0.2 g/kg; P = 0.003) and RV masses (0.8 ± 0.1 to 0.6 ± 0.1 g/kg; P < 0.001), and the length of the major axis of the LV (90 ± 6 to 84 ± 7 mm. P < 0.001), similar to what has been observed previously in men (8.0%; Perhonen MA, Franco F, Lane LD, Buckey JC, Blomqvist Zerwekh JE, Peshock RM, Weatherall PT, Levine BD. J Appl Physiol 91: 645–653, 2001). In contrast, there were no significant reductions in LV or RV volumes in the exercise-trained group, and the length of the major axis was preserved. Moreover, there were significant increases in LV (1.9 ± 0.4 to 2.3 ± 0.3 g/kg; P < 0.001) and RV masses (0.7 ± 0.1 to 0.8 ± 0.2 g/kg; P = 0.002), as well as mean wall thickness (9 ± 2 to 11 ± 1 mm; P = 0.02). The interaction between sedentary and exercise LV and RV masses was highly significant ( P < 0.0001). Protein and BCAA supplementation led to an intermediate phenotype with no change in LV or RV mass after bed rest, but there remained a significant reduction in LV volume (103 ± 14 to 80 ± 16 ml; P = 0.02) and major-axis length (91 ± 5 to 88 ± 7 mm; P = 0.003). All subjects lost an equivalent amount of body mass (3.4 ± 0.2 kg control; 3.1 ± 0.04 kg exercise; 2.8 ± 0.1 kg protein). Cardiac atrophy occurs in women similar to men following sedentary 60 days HDT bed rest. However, exercise training and, to a lesser extent, protein supplementation may be potential countermeasures to the cardiac atrophy associated with chronic unloading conditions such as in spaceflight and prolonged bed rest.
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Miokovic, Tanja, Gabriele Armbrecht, Dieter Felsenberg et Daniel L. Belavý. « Heterogeneous atrophy occurs within individual lower limb muscles during 60 days of bed rest ». Journal of Applied Physiology 113, no 10 (15 novembre 2012) : 1545–59. http://dx.doi.org/10.1152/japplphysiol.00611.2012.
Texte intégralRésumé :
To better understand disuse muscle atrophy, via magnetic resonance imaging, we sequentially measured muscle cross-sectional area along the entire length of all individual muscles from the hip to ankle in nine male subjects participating in 60-day head-down tilt bed rest (2nd Berlin BedRest Study; BBR2–2). We hypothesized that individual muscles would not atrophy uniformly along their length such that different regions of an individual muscle would atrophy to different extents. This hypothesis was confirmed for the adductor magnus, vasti, lateral hamstrings, medial hamstrings, rectus femoris, medial gastrocnemius, lateral gastrocnemius, tibialis posterior, flexor hallucis longus, flexor digitorum longus, peroneals, and tibialis anterior muscles ( P ≤ 0.004). In contrast, the hypothesis was not confirmed in the soleus, adductor brevis, gracilis, pectineus, and extensor digitorum longus muscles ( P ≥ 0.20). The extent of atrophy only weakly correlated ( r = −0.30, P < 0.001) with the location of greatest cross-sectional area. The rate of atrophy during bed rest also differed between muscles ( P < 0.0001) and between some synergists. Most muscles recovered to their baseline size between 14 and 90 days after bed rest, but flexor hallucis longus, flexor digitorum longus, and lateral gastrocnemius required longer than 90 days before recovery occurred. On the basis of findings of differential atrophy between muscles and evidence in the literature, we interpret our findings of intramuscular atrophy to reflect differential disuse of functionally different muscle regions. The current work represents the first lower-limb wide survey of intramuscular differences in disuse atrophy. We conclude that intramuscular differential atrophy occurs in most, but not all, of the muscles of the lower limb during prolonged bed rest.
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Tajima, Hiroshi, Hiroo Matsuse, Ryuki Hashida, Takeshi Nago, Masafumi Bekki, Sohei Iwanaga, Eriko Higashi et Naoto Shiba. « Electrically stimulated eccentric contraction during non-weight bearing knee bending exercise in the supine position increases oxygen uptake : A randomized, controlled, exploratory crossover trial ». PLOS ONE 16, no 11 (18 novembre 2021) : e0259856. http://dx.doi.org/10.1371/journal.pone.0259856.
Texte intégralRésumé :
It is well known that prolonged bed rest induces muscle weakness, muscle atrophy, cardiovascular deconditioning, bone loss, a loss of functional capacity, and the development of insulin resistance. Neuromuscular electrical stimulation is anticipated to be an interventional strategy for disuse due to bed rest. A hybrid training system (HTS), synchronized neuromuscular electrical stimulation for voluntary exercise using an articular motion sensor, may increase the exercise load though bed rest. We assessed oxygen uptake or heart rate during knee bending exercise in the supine position on a bed both simultaneously combined with HTS and without HTS to evaluate exercise intensity on different days in ten healthy subjects (8 men and 2 women) by a randomized controlled crossover trial. The values of relative oxygen uptake during knee bending exercise with HTS were significantly greater than those during knee bending exercise without HTS (7.29 ± 0.91 ml/kg/min vs. 8.29 ± 1.06 ml/kg/min; p = 0.0115). That increment with HTS was a mean of 14.42 ± 13.99%. Metabolic equivalents during knee bending exercise with HTS and without HTS were 2.08 ± 0.26 and 2.39 ± 0.30, respectively. The values of heart rate during knee bending exercise with HTS were significantly greater than those during knee bending exercise without HTS (80.82 ± 9.19 bpm vs. 86.36 ± 5.50 bpm; p = 0.0153). HTS could increase exercise load during knee bending exercise which is easy to implement on a bed. HTS might be a useful technique as a countermeasure against the disuse due to bed rest, for example during acute care or the quarantine for infection prophylaxis.
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Wang, Fei, Jing Wang, Jian He, Wenjiong Li, Jinglong Li, Shengju Chen, Peng Zhang, Hongju Liu et Xiaoping Chen. « Serum miRNAs miR-23a, 206, and 499 as Potential Biomarkers for Skeletal Muscle Atrophy ». BioMed Research International 2017 (2017) : 1–9. http://dx.doi.org/10.1155/2017/8361237.
Texte intégralRésumé :
Muscle biopsy has long been expected to be replaced by noninvasive biomarkers with diagnostic value and prognostic applications for muscle atrophy. Growing evidence suggests that circulating microRNAs (miRNAs) could act as biomarkers for numerous pathophysiological statuses. In the present study, our results showed that the serum levels of six muscle-specific miRNAs (miR-1/23a/133/206/208b/499) were all elevated in unloading induced mice. The medium levels of these six muscle-specific miRNAs were all elevated in starvation induced atrophic C2C12 myotubes. Moreover, the serum levels of miR-23a/206/499 were induced in participants after 45 days of head-down bed rest (HDBR). The levels of miR-23a/206/499 were positively correlated with the ratio of soleus volume loss in HDBR participants, indicating that they might represent the process of muscle loss. In conclusion, our results demonstrated that circulating miRNAs could serve as useful biochemical and molecular indicators for muscle atrophy diagnosis and disease progression.
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Kozàkovà, Michaela, Emona Malshi, Carmela Morizzo, Stefano Pedri, Francesca Santini, Gianni Biolo, Massimo Pagani et Carlo Palombo. « Impact of prolonged cardiac unloading on left ventricular mass and longitudinal myocardial performance : an experimental bed rest study in humans ». Journal of Hypertension 29, no 1 (janvier 2011) : 137–43. http://dx.doi.org/10.1097/hjh.0b013e32833f5e01.
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Sharlo, Kristina, Inna Paramonova, Olga Turtikova, Sergey Tyganov et Boris Shenkman. « Plantar mechanical stimulation prevents calcineurin-NFATc1 inactivation and slow-to-fast fiber type shift in rat soleus muscle under hindlimb unloading ». Journal of Applied Physiology 126, no 6 (1 juin 2019) : 1769–81. http://dx.doi.org/10.1152/japplphysiol.00029.2019.
Texte intégralRésumé :
The prevailing myosin isoform [myosin heavy chain (MyHC)] in a skeletal muscle determines contractile properties of the muscle. Under actual or simulated microgravity conditions such as human bed rest or rat hindlimb unloading, decrease in expression of MyHC of the slow type [MyHC I(β)] has been observed. It was demonstrated that increasing sensory input by performing plantar mechanical stimulation (PMS) on the soles of the feet results in an increase in neuromuscular activation of the lower limb muscles and may prevent slow-to-fast fiber type shift. The calcineurin-nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) signaling pathway is the main cascade regulating MyHC I(β) expression. The present study was aimed to analyze the states of the calcineurin-NFATc1 signaling cascade under conditions of PMS during rat hindlimb unloading. Male Wistar rats were randomly assigned to vivarium control groups and 1-day unloading (1HS), 3-day unloading (3HS), 1HS+PMS, and 3HS+PMS groups. We found that both 1 day and 3 days of unloading caused decrease in MyHC I(β) mRNA expression and decrease in glycogen synthase kinase-3β phosphorylation (Ser 9) that brought about the kinase activation, and these effects of unloading were prevented by PMS. Three days of unloading also caused increase in expression of calsarcin-2 (myozenin-I), which was found to be the endogenous calcineurin inhibitor. The level of calsarcin-2 expression in the 3HS+PMS group did not differ from the control group. Therefore, we conclude that PMS upregulates the calcineurin-NFATc1 signaling pathway and prevents unloading-induced MyHC I(β) decrease. NEW & NOTEWORTHY It is widely accepted that changes in the myosin phenotype during functional unloading (disuse) are determined by a decreased expression of the myosin heavy chain (MyHC) I(β) gene, and this decrease leads to changes of contractile and fatigue characteristics of soleus muscle. The calcineurin-nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) pathway is one of the most important signaling cascades regulating slow MyHC isoform expression. The present study is the first to show that plantar mechanical stimulation upregulates calcineurin-NFATc1 signaling in soleus muscles of hindlimb-unloaded rats.
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Delp, M. D., M. Brown, M. H. Laughlin et E. M. Hasser. « Rat aortic vasoreactivity is altered by old age and hindlimb unloading ». Journal of Applied Physiology 78, no 6 (1 juin 1995) : 2079–86. http://dx.doi.org/10.1152/jappl.1995.78.6.2079.
Texte intégralRésumé :
Prolonged bed rest in young adults leads to a number of cardiovascular alterations, including orthostatic intolerance and decreased exercise capacity. Similar changes occur with advanced age. These modifications of cardiovascular function have been suggested to be causally related to changes in peripheral vascular reactivity. Using rat hindlimb unloading as an animal model of physical inactivity, this study was designed to determine whether prolonged decreases in weight-bearing activity induce changes in vascular reactivity that are similar to those occurring in senescent rats and whether the imposition of inactivity on old rats further modifies any age-related alterations in vasomotor responsiveness. Responses to vasoactive compounds were examined in vitro by using isolated abdominal aortic rings. Maximal isometric contractile force evoked by the vasoconstrictors KCl, norepinephrine (NE), and arginine vasopressin was lower in aortic segments from young hindlimb-unloaded (YHU), old control (OC), and old hindlimb-unloaded (OHU) rats compared with that from young control (YC) rats. Sensitivity [mean effective concentration (EC50)] to KCl was enhanced in segments from both old and unloaded animals compared with YC rats, but EC50 values for the other constrictors were not different among groups. Vasorelaxation responses induced by acetylcholine (10(-7) M NE preconstriction) were lower in vessel rings from OC (1 x 10(-7) to 3 x 10(-6) M), YHU (10(-7) to 10(-5) M), and OHU (10(-7) to 10(-5) M) rats than those from YC animals. In addition, vessel rings from OC, YHU, and OHU rats were less sensitive to sodium nitroprusside-induced relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)
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Trappe, Scott, Andrew Creer, Kiril Minchev, Dustin Slivka, Emily Louis, Nicholas Luden et Todd Trappe. « Human soleus single muscle fiber function with exercise or nutrition countermeasures during 60 days of bed rest ». American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 294, no 3 (mars 2008) : R939—R947. http://dx.doi.org/10.1152/ajpregu.00761.2007.
Texte intégralRésumé :
The soleus muscle has been consistently shown to atrophy more than other leg muscles during unloading and is difficult to protect using various exercise countermeasure paradigms. However, the efficacy of aerobic exercise, a known stimulus for oxidative adaptations, has not been tested in combination with resistance exercise (RE), a known hypertrophic stimulus. We hypothesized that a concurrent exercise program (AE + RE) would preserve soleus fiber myosin heavy chain (MHC) I size and function during 60 days of bed rest. A secondary objective was to test the hypothesis that a leucine-enriched high protein diet would partially protect soleus single fiber characteristics. Soleus muscle biopsies were obtained before and after bed rest from a control (BR; n = 7), nutrition (BRN; n = 8), and exercise (BRE; n = 6) group. Single muscle fiber diameter (Dia), peak force (Po), contractile velocity, and power were studied. BR decreased ( P < 0.05) MHC I Dia (−14%), Po (−38%), and power (−39%) with no change in contractile velocity. Changes in MHC I size (−13%) and contractile function (∼30%) from BRN were similar to BR. BRE decreased ( P < 0.05) MHC I Dia (−13%) and Po (−23%), while contractile velocity increased ( P < 0.05) 26% and maintained power. These soleus muscle data show 1) the AE + RE exercise program maintained MHC I power but not size and strength, and 2) the nutrition countermeasure did not benefit single fiber size and contractile function. The divergent response in size and functional MHC I soleus properties with the concurrent exercise program was a unique finding further highlighting the challenges of protecting the unloaded soleus.
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Bamman, Marcas M., Mark S. F. Clarke, Daniel L. Feeback, Robert J. Talmadge, Bruce R. Stevens, Steven A. Lieberman et Michael C. Greenisen. « Impact of resistance exercise during bed rest on skeletal muscle sarcopenia and myosin isoform distribution ». Journal of Applied Physiology 84, no 1 (1 janvier 1998) : 157–63. http://dx.doi.org/10.1152/jappl.1998.84.1.157.
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Bamman, Marcas M., Mark S. F. Clarke, Daniel L. Feeback, Robert J. Talmadge, Bruce R. Stevens, Steven A. Lieberman, and Michael C. Greenisen. Impact of resistance exercise during bed rest on skeletal muscle sarcopenia and myosin isoform distribution. J. Appl. Physiol. 84(1): 157–163, 1998.—Because resistance exercise (REx) and bed-rest unloading (BRU) are associated with opposing adaptations, our purpose was to test the efficacy of REx against the effects of 14 days of BRU on the knee-extensor muscle group. Sixteen healthy men were randomly assigned to no exercise (NoEx; n = 8) or REx ( n = 8). REx performed five sets of leg press exercise with 80–85% of one repetition maximum (1 RM) every other day during BRU. Muscle samples were removed from the vastus lateralis muscle by percutaneous needle biopsy. Myofiber distribution was determined immunohistochemically with three monoclonal antibodies against myosin heavy chain (MHC) isoforms (I, IIa, IIx). MHC distribution was further assessed by quantitative gel electrophoresis. Dynamic 1-RM leg press and unilateral maximum voluntary isometric contraction (MVC) were determined. Maximal neural activation (root mean squared electromyogram) and rate of torque development (RTD) were measured during MVC. Reductions ( P < 0.05) in type I (15%) and type II (17%) myofiber cross-sectional areas were found in NoEx but not in REx. Electrophoresis revealed no changes in MHC isoform distribution. The percentage of type IIx myofibers decreased ( P < 0.05) in REx from 9 to 2% and did not change in NoEx. 1 RM was reduced ( P < 0.05) by 9% in NoEx but was unchanged in REx. MVC fell by 15 and 13% in NoEx and REx, respectively. The agonist-to-antagonist root mean squared electromyogram ratio decreased ( P < 0.05) 19% in REx. RTD slowed ( P < 0.05) by 54% in NoEx only. Results indicate that REx prevented BRU-induced myofiber atrophy and also maintained training-specific strength. Unlike spaceflight, BRU did not induce shifts in myosin phenotype. The reported benefits of REx may prove useful in prescribing exercise for astronauts in microgravity.
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Kozakova, M., C. Palombo, G. Bini, E. Malshi, C. Morizzo, F. Santini, P. Salvi et M. Pagani. « LARGE ARTERY FUNCTION AND VENTRICULAR ARTERIAL COUPLING FOLLOWING CARDIOVASCULAR UNLOADING RELATED TO PROLONGED BED REST IN YOUNG HEALTHY SUBJECTS : PP.31.218 ». Journal of Hypertension 28 (juin 2010) : e515. http://dx.doi.org/10.1097/01.hjh.0000379756.25562.92.
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Caiozzo, V. J., F. Haddad, S. Lee, M. Baker, William Paloski et K. M. Baldwin. « Artificial gravity as a countermeasure to microgravity : a pilot study examining the effects on knee extensor and plantar flexor muscle groups ». Journal of Applied Physiology 107, no 1 (juillet 2009) : 39–46. http://dx.doi.org/10.1152/japplphysiol.91130.2008.
Texte intégralRésumé :
The goal of this project was to examine the effects of artificial gravity (AG) on skeletal muscle strength and key anabolic/catabolic markers known to regulate muscle mass. Two groups of subjects were selected for study: 1) a 21 day-bed rest (BR) group ( n = 7) and 2) an AG group ( n = 8), which was subjected to 21 days of 6° head-down tilt bed rest plus daily 1-h exposures to AG (2.5 G at the feet). Centrifugation was produced using a short-arm centrifuge with the foot plate ∼220 cm from the center of rotation. The torque-velocity relationships of the knee extensors and plantar flexors of the ankle were determined pre- and posttreatment. Muscle biopsy samples obtained from the vastus lateralis and soleus muscles were used for a series of gene expression analyses (mRNA abundance) of key factors implicated in the anabolic vs. catabolic state of the muscle. Post/pre torque-velocity determinations revealed greater decrements in knee extensor performance in the BR vs. AG group ( P < 0.04). The plantar flexors of the AG subjects actually demonstrated a net gain in the torque-velocity relationship, whereas in the BR group, the responses declined (AG vs. BR, P < 0.001). Muscle fiber cross-sectional area decreased by ∼20% in the BR group, whereas no losses were evident in the AG group. RT-PCR analyses of muscle biopsy specimens demonstrated that markers of growth and cytoskeletal integrity were higher in the AG group, whereas catabolic markers were elevated in the BR group. Importantly, these patterns were seen in both muscles. We conclude that paradigms of AG have the potential to maintain the functional, biochemical, and structural homeostasis of skeletal muscle in the face of chronic unloading.