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PubMed1997

Upright exercise or supine lower body negative pressure exercise maintains exercise responses after bed rest.

Adaptation to bed rest or space flight is accompanied by an impaired ability to exercise in an upright position. We hypothesized that a daily, 30-min bout of intense, interval exercise in upright posture or supine against lower body negative pressure (LBNP) would maintain upright exercise heart rate and respiratory responses after bed rest. Twenty-four men (31 +/- 3 yr) underwent 5 d of 6 degree head-down tilt: eight performed no exercise (CON), eight performed upright treadmill exercise (UPex), and eight performed supine treadmill exercise against LBNP at -51.3 +/- 0.4 mm Hg (LBNPex). Submaximal treadmill exercise responses (56, 74, and 85% of VO2peak) were measured pre- and post-bed rest. In CON, submaximal heart rate, respiratory exchange ratio, and ventilation were significantly greater (P < or = 0.05) after bed rest. In UPex and LBNPex, submaximal exercise responses were similar pre- and post-bed rest. Our results indicate that a daily 30-min bout of intense, interval upright exercise training or supine exercise training against LBNP is sufficient to maintain upright exercise responses after 5 d of bed rest. These results may have important implications for the development of exercise countermeasures during space flight.

Adult↗
PubMed2002

Branched-chain amino acid supplementation during bed rest: effect on recovery.

Bed rest is associated with a loss of protein from the weight-bearing muscle. The objectives of this study are to determine whether increasing dietary branched-chain amino acids (BCAAs) during bed rest improves the anabolic response after bed rest. The study consisted of a 1-day ambulatory period, 14 days of bed rest, and a 4-day recovery period. During bed rest, dietary intake was supplemented with either 30 mmol/day each of glycine, serine, and alanine (group 1) or with 30 mmol/day each of the three BCAAs (group 2). Whole body protein synthesis was determined with U-(15)N-labeled amino acids, muscle, and selected plasma protein synthesis with l-[(2)H(5)]phenylalanine. Total glucose production and gluconeogenesis from alanine were determined with l-[U-(13)C(3)]alanine and [6,6-(2)H(2)]glucose. During bed rest, nitrogen (N) retention was greater with BCAA feeding (56 +/- 6 vs. 26 +/- 12 mg N. kg(-1). day(-1), P < 0.05). There was no effect of BCAA supplementation on either whole body, muscle, or plasma protein synthesis or the rate of 3-MeH excretion. Muscle tissue free amino acid concentrations were increased during bed rest with BCAA (0.214 +/- 0.066 vs. 0.088 +/- 0.12 nmol/mg protein, P < 0.05). Total glucose production and gluconeogenesis from alanine were unchanged with bed rest but were significantly reduced (P < 0.05) with the BCAA group in the recovery phase. In conclusion, the improved N retention during bed rest is due, at least in part, to accretion of amino acids in the tissue free amino acid pools. The amount accreted is not enough to impact protein kinetics in the recovery phase but does improve N retention by providing additional essential amino acids in the early recovery phase.

Adult↗
PubMed2002

Biochemical and hemodynamic changes in normal subjects during acute and rigorous bed rest and ambulation.

Rigorous bed rest (RBR) induces significant biochemical and circulatory changes. However, little is known about acute rigorous bed rest (ARBR). Measuring biochemical and circulatory variables during ARBR and RBR the aim of this study was to establish the significance of ARBR effect. Studies were done during 3 days of a pre-bed rest (BR) period and during 7 days of ARBR and RBR period. Thirty normal male individuals aged, 24.1 +/- 6.3 years were chosen as subjects. They were divided equally into three groups: 10 subjects placed under active control conditions served as unrestricted ambulatory control subjects (UACS), 10 subjects submitted to an acute rigorous bed rest served as acute rigorous bed rested subjects (ARBRS) and 10 subjects submitted to a rigorous bed rest served as rigorous bed rested subjects (RBRS). The UACS were maintained under an average running distance of 9.7 km day-1. For the ARBR effect simulation, ARBRS were submitted abruptly to BR for 7 days. They did not have any prior knowledge of the exact date and time when they would be asked to confine to RBR. For the RBR effect simulation, RBRS were subjected to BR for 7 days on a predetermined date and time known to them right away from the start of the study. Plasma renin activity (PRA), plasma cortisol (PC), plasma aldosterone (PA), plasma and urinary sodium (Na) and potassium (K) levels, heart rate (HR), cardiac output (CO), and arterial blood pressure (ABP) increased significantly, and urinary aldosterone (UA), stroke volume (SV) and plasma volume (PV) decreased significantly (p<0.05) in ARBRS and RBRS as compared with their pre-BR values and the values in UACS. Electrolyte, hormonal and hemodynamic responses were significantly (p<0.05) greater and occurred significantly faster (p<0.05) during ARBR than RBR. Parameters change insignificantly (p>0.05) in UACS compared with pre-BR control values. It was concluded that, the more abruptly muscular activity is restricted in experimental subjects while they are very active, the greater hemodynamic and biochemical change there is and probably in individuals whose muscular activity is abruptly terminated after an accident or sudden illness.

Adaptation, Physiological↗
PubMed2000

Body temperature and skin blood flow during a 14-day bed-rest in a head-down tilt position in humans.

Exposure to microgravity or simulated microgravity is known to affect regulatory function in autonomic nervous system. With regard to thermoregulation, simulated microgravity impairs sweating and induces lower skin and higher internal temperatures during physical work. During supine rest after HDT bed rest, the internal temperatures were reported to be higher than those of pre-HDT bed rest in some studies but not in others. There is no report about the dynamic changes of skin blood flow during 14-day HDT bed rest. The process of HDT bed-rest deconditioning on the function of the thermoregulatory system is virtually unknown. The HDT induces an immediate cephalad fluid shift which would inhibit the sympathetic outflow through the arterial and cardiopulmonary baroreflexes, which may increase the skin blood flow. On the other hand, prolonged HDT bed rest induces dehydration, which will increase sympathetic outflow through cardiopulmonary baroreceptor modulation. Both sympathetic activation and dehydration itself will decrease skin blood flow. It seems probable that the general effect on skin blood flow may reverse along the HDT bed rest. However, the dynamic characters of skin blood flow and body temperature during the HDT bed rest have not been studied thoroughly. Therefore, the purpose of present study was to investigate the changes of skin blood flow and body temperature during 14 days HDT bed rest.

Adult↗
PubMed1995

Do patients need to remain in bed following embryo transfer? The Birmingham experience of 103 in-vitro fertilization cycles with no bed rest following embryo transfer.

Since the early days of human in-vitro fertilization and embryo transfer, rest in bed for hours immediately following the transfer has been advocated and widely practised. However, there is no scientific validation for this practice which is both time-consuming for the patient and increases space occupancy in the hospital or clinic. We report here on a study of 103 in-vitro fertilization cycles with no bed rest in hospital following the embryo transfer. The mean number of embryos transferred was 2.7 (range 1-3) and the clinical pregnancy rate per embryo transfer procedure was 40%. These results suggest that bed rest is not necessary following embryo transfer.

Adult↗
PubMed1984

Physiological responses to prolonged bed rest and fluid immersion in humans.

Rest in bed and immersion in water have been used for centuries by physicians and healers in treating injury and disease. The qualitative similarity of acute and chronic responses to bed rest, immersion, and weightlessness has sparked renewed interest in and a resultant greater understanding of the mechanisms of disuse deconditioning. Some combination of changes in hydrostatic pressure, reduced total metabolism (exercise), compression force on weight-bearing bones, as well as psychological factors associated with prolonged confinement in a new environment probably comprise the major input stimuli for the adaptive responses. Virtually every physiological system is affected. Early responses involve the fluid, electrolyte, and blood pressure control systems with significant muscular atrophy and decreases in bone density occurring over weeks and months. Much effort has been expended to describe the various responses to bed rest and immersion with understandably less effort devoted to research during weightlessness. Future research should be directed mainly toward an understanding of the mechanisms of these adaptive responses. Additional work is especially needed to elucidate the effects of deconditioning on drug metabolism, functioning of the immune system, carbohydrate metabolism, protein and peptide metabolism in muscle, and calcium metabolism as it affects integrity of bone.

Adaptation, Physiological↗
PubMed1985

Epinephrine, norepinephrine, and dopamine during a 4-day head-down bed rest.

Head-down bed rest at an angle of 6 degrees was used as an experimental model to simulate the hemodynamic effects of microgravity, i.e., the shift of fluids from the lower to the upper part of the body. The sympathoadrenal activity during acute (from 0.5 to 10 h) and prolonged (4 days) head-down bed rest was assessed in eight healthy men (24 +/- 1 yr) by measuring epinephrine (E), norepinephrine (NE), dopamine (DA), and methoxylated metabolite levels in their plasma and urine. Catecholamine (CA) and methoxyamine levels were essentially unaltered at any time of bed rest. Maximal changes in plasma were on the second day (D2): NE, 547 +/- 84 vs. 384 +/- 55 pg/ml; DA, 192 +/- 32 vs. 141 +/- 16 pg/ml; NS. After 24 h of bed rest, heart rate decreased from 71 +/- 1 to 63 +/- 3/min (P less than 0.01). Daily dynamic leg exercise [50% maximum O2 uptake (VO2 max)] used as a countermeasure did not alter the pattern of plasma CA during bed rest but resulted in a higher urinary NE excretion during postexercise recovery (+45% on D2; P less than 0.05). The data indicate no evident relationship between sympathoadrenal function and stimulation of cardiopulmonary receptors or neuroendocrine changes induced by central hypervolemia during head-down bed rest.

Adult↗
PubMed2004

Bed rest for acute low-back pain and sciatica.

BACKGROUND: Low-back pain (LBP) is a common reason for consulting a general practitioner, and advice on daily activities is an important part of the primary care management of low-back pain. OBJECTIVES: To assess the effects of advice to rest in bed for patients with acute LBP or sciatica. SEARCH STRATEGY: We searched the Cochrane Back Group Specialized Registry, CENTRAL, MEDLINE, EMBASE, Sport, and SCISEARCH to March 2003, reference lists of relevant articles, and contacted authors of relevant articles. SELECTION CRITERIA: Randomised or controlled clinical trials with quasi-randomisation (alternate allocation, case record numbers, dates of birth, etc.), in any language, where the effectiveness of advice to rest in bed was evaluated. The main outcomes of interest were pain, functional status, recovery and return to work. DATA COLLECTION AND ANALYSIS: Two reviewers independently selected trials for inclusion, assessed the internal validity of included trials and extracted data. Investigators were contacted to obtain missing information. MAIN RESULTS: Eleven trials (1963 patients) were included in this updated version. There is high quality evidence that people with acute LBP who are advised to rest in bed have a little more pain [Standardised Mean Difference (SMD) 0.22 (95% Confidence Interval (CI): 0.02, 0.41)] and a little less functional recovery [SMD 0.29 (95% CI: 0.05, 0.45)] than those advised to stay active. For patients with sciatica, there is moderate quality evidence of little or no difference in pain [SMD -0.03 (95% CI: -0.24, 0.18)] or functional status [SMD 0.19 (95% CI: -0.02, 0.41)] between bed rest and staying active. For patients with acute LBP, there is moderate quality evidence of little or no difference in pain intensity or functional status between bed rest and exercises. For patients with sciatica, there is moderate quality evidence of little or no difference in pain intensity between bed rest and physiotherapy, but small improvements in functional status [Weighted Mean Difference 6.9 (on a 0-100 scale) (95% CI: 1.09, 12.74)] with physiotherapy. There is moderate quality evidence of little or no difference in pain intensity or functional status between two to three days and seven days of bed rest. REVIEWERS' CONCLUSIONS: For people with acute LBP, advice to rest in bed is less effective than advice to stay active. For patients with sciatica, there is little or no difference between advice to rest in bed and advice to stay active. There is little or no difference in the effect of bed rest compared to exercises or physiotherapy, or seven days of bed rest compared with two to three.

Acute Disease↗
PubMed2003

Diurnal variation of aldosterone and plasma renin activity: timing relation to melatonin and cortisol and consistency after prolonged bed rest.

Exposure to prolonged bed rest is known to induce changes in the renin-angiotensin-aldosterone system (RAAS) by way of posture, sodium and potassium balance, and stress, which may have serious consequences for patients. We focused on the diurnal variation of the RAAS by investigating changes in the levels of plasma renin activity (PRA) and aldosterone; for comparison to markers of the intrinsic pacemaker and to stress, we measured melatonin and cortisol. PRA, aldosterone, melatonin, and cortisol were measured hourly in 10 normal subjects with standardized sleep patterns, posture, and diet at baseline and after 11 days of prolonged bed rest conducted under a light-dark cycle. Circadian characteristics of hormone secretion patterns were estimated by multiple harmonic regression with excellent goodness-of-fit measures. Variability in the melatonin and cortisol patterns across subjects was minimal. Even for pulsatile hormones, this technique successfully estimated the acrophase, which was the salient feature. Baseline hormone peak times started with melatonin near the middle of the sleep period, followed by PRA, then aldosterone, and then cortisol around wake time. Prolonged bed rest did not induce significant changes in any timing characteristic of the secretion patterns. Baseline and prolonged bed rest peak times for melatonin and cortisol and amplitude characteristics for all hormones were highly correlated, indicating consistency within individuals. These data provide strong evidence that prolonged bed rest of 11 days' duration does not disrupt either the timing characteristics of the RAAS or the intrinsic pacemaker.

Adult↗
PubMed2004

Intravenous pamidronate prevents femoral bone loss and renal stone formation during 90-day bed rest.

UNLABELLED: Long-term bed rest has potential risks of bone loss and renal stone formation. We examined the effects of resistive exercise and intravenous pamidronate on BMD, bone turnover, urinary calcium, and renal stone formation in 25 healthy males during 90-day bed rest. Pamidronate prevented femoral bone loss and renal stone formation, but resistive exercise showed little effects. INTRODUCTION: Long-term bed rest increases the risks of bone loss and urinary stone formation. Resistive exercise increases bone formation, and bisphosphonates reduce bone resorption. However, the effects of muscle exercise and bisphosphonates have not been examined side-by-side. The objectives of this study are to compare the effects of pamidronate with resistive exercise on BMD and renal stone formation during prolonged bed rest. MATERIALS AND METHODS: Twenty-five male white volunteers, 26-45 years of age, were randomly assigned to the control (n = 9), exercise (n = 9), and pamidronate (n = 7) groups and underwent 90-day 6 degrees head-down tilt bed rest. Exercise group performed squats and heel raises on a flywheel device for 30 minutes every 3 days. Pamidronate (60 mg) was administered intravenously 14 days before bed rest. BMD of the head, forearm, lumbar spine, and proximal femur; biochemical bone markers; calcium (Ca) metabolism; and abdominal radiographs were examined during 90 days of bed rest and 360 days of reloading. RESULTS: In controls, proximal femoral BMD decreased, and bone resorption markers and urinary Ca increased during bed rest, along with development of renal stones in two of nine subjects. Resistive exercise increased bone formation but was unable to prevent femoral BMD decrease and increases in bone resorption and urinary Ca during bed rest, with formation of renal stones in four of nine subjects. Pamidronate maintained femoral BMD, reduced bone resorption and urinary Ca, and completely prevented renal stone formation. CONCLUSIONS: Resistive exercise increased bone formation but could not reduce bone resorption and the risk of renal stones. In contrast, inhibition of bone resorption by pamidronate could preserve bone mineral and reduce the risk of renal stone formation during prolonged bed rest.

Adult↗
PubMed2002

Fluid volume compartments and biochemical measurements for disclosing fluid depletion during acute and rigorous bed rest in normal subjects.

Rigorous bed rest (RBR) induces fluid depletion, however, little is known about the mechanisms of development of fluid depletion during acute bed rest (ABR). Measuring fluid retention and body hydration parameters, the aim of this study was to establish whether ABR than RBR could depress significantly more fluid retention contributing to greater fluid depletion development. Studies were conducted during pre bed rest (BR) period of three days and during seven days period of ABR and RBR. Thirty normal male individuals aged, 24.2 +/- 5.0 years chosen as subjects. They were divided into three groups: unrestricted ambulatory control subjects (UACS), acute bed rested subjects (ABRS) and rigorous bed rested subjects (RBRS). Acute bed rested subjects confined abruptly to RBR, while they did not have any prior knowledge of the exact date and time when they would be asked to stay in bed. Rigorous bed rested subjects submitted to RBR on a predetermined date and time known to them right from the start of the study. Unrestricted ambulatory control subjects were not confined to any type of bed rest. Fluid loss, urinary and plasma sodium (Na+) and potassium (K+), urinary osmolality and plasma osmolality, whole blood hematocrit (Hct), whole blood hemoglobin (Hb), and total plasma protein increased significantly (p < 0.05) with time, while fluid retention, extracellular volume (ECV), plasma volume (PV), red cell volume (RCV), blood volume (BV), interstitial volume (IV) and fluid intakes reduced significantly (p < 0.05) with time in ABRS and RBRS compared with their pre-BR values and the control values (UACS). However, the measured parameters changed significantly (p < 0.05) more with time in ABRS than RBRS. Fluid rention, fluid loss, fluid intake, urinary and plasma Na+ and K+, Hct, Hb, plasma protein, urinary and plasma osmolality, ECV, PV, RCV, BV and IV did not change in UACS compared with their pre-BR values. It was concluded that significant increase of urinary and plasma osmolality, whole blood Hct and Hb, total plasma protein, plasma Na+ and K+, and significant decrease of ECV, PV, RCV, BV, and IV may demonstrate fluid depleteion, while a higher increase of fluid loss in spite of fluid depletion may show decreased fluid retention. Dissociation between fluid losses and fluid depletion may suggest the presence of impair fluid retention as a mechanism of development of fluid depletion.

Adult↗
PubMed1997

The interplay of central and peripheral factors in limiting maximal O2 consumption in man after prolonged bed rest.

1. The effects of bed rest on the cardiovascular and muscular parameters which affect maximal O2 consumption (VO2,max) were studied. The fractional limitation of VO2,max imposed by these parameters after bed rest was analysed. 2. The VO2,max, by standard procedure, and the maximal cardiac output (Qmax), by the pulse contour method, were measured during graded cyclo-ergometric exercise on seven subjects before and after a 42-day head-down tilt bed rest. Blood haemoglobin concentration ([Hb]) and arterialized blood gas analysis were determined at the highest work load. 3. Muscle fibre types, oxidative enzyme activities, and capillary and mitochondrial densities were measured on biopsy samples from the vastus lateralis muscle before and at the end of bed rest. The measure of muscle cross-sectional area (CSA) by NMR imaging at the level of biopsy site allowed computation of muscle oxidative capacity and capillary length. 4. The VO2,max was reduced after bed rest (-16.6%). The concomitant decreases in Qmax (-30.8%), essentially due to a change in stroke volume, and in [Hb] led to a huge decrease in O2 delivery (-39.7%). 5. Fibre type distribution was unaffected by bed rest. The decrease in fibre area corresponded to the significant reduction in muscle CSA (-17%). The volume density of mitochondria was reduced after bed rest (-16.6%), as were the oxidative enzyme activities (-11%). The total mitochondrial volume was reduced by 28.5%. Capillary density was unchanged. Total capillary length was 22.2% lower after bed rest, due to muscle atrophy. 6. The interaction between these muscular and cardiovascular changes led to a smaller reduction in VO2,max than in cardiovascular O2 transport. Yet the latter appears to play the greatest role in limiting VO2,max after bed rest (> 70% of overall limitation), the remaining fraction being shared between peripheral O2 diffusion and utilization.

Adult↗
PubMed1975

Assessment of the degradation of thyroid hormones in man during bed rest.

The effect of bed rest on the absolute turnover rates of thyroid hormones, thyroxine (T4) and triiodothyronine (T3), was evaluated in man. Bed rest resulted in physical deconditioning, measured by a decreased rate of maximal oxygen consumption; physical deconditioning was associated with no significant alterations in the metabolic clearance of T4 and T3. Plasma concentrations of these iodothyronines were not changed as a result of bed rest. Absolute hormone turnover rates were similar in control and bed-rest subjects. The data suggest that the degradation of thyroid hormones is not influenced by physical deconditioning or hypodynamia.

Adolescent↗
PubMed2000

Supine lower body negative pressure exercise during bed rest maintains upright exercise capacity.

Bed rest and spaceflight reduce exercise fitness. Supine lower body negative pressure (LBNP) treadmill exercise provides integrated cardiovascular and musculoskeletal stimulation similar to that imposed by upright exercise in Earth gravity. We hypothesized that 40 min of supine exercise per day in a LBNP chamber at 1.0-1.2 body wt (58 +/- 2 mmHg LBNP) maintains aerobic fitness and sprint speed during 15 days of 6 degrees head-down bed rest (simulated microgravity). Seven male subjects underwent two such bed-rest studies in random order: one as a control study (no exercise) and one with daily supine LBNP treadmill exercise. After controlled bed-rest, time to exhaustion during an upright treadmill exercise test decreased 10%, peak oxygen consumption during the test decreased 14%, and sprint speed decreased 16% (all P < 0.05). Supine LBNP exercise during bed rest maintained all the above variables at pre-bed-rest levels. Our findings support further evaluation of LBNP exercise as a countermeasure against long-term microgravity-induced deconditioning.

Adult↗
PubMed2001

Electrolyte changes in plasma and urine of athletes during acute and rigorous bed rest and ambulatory conditions.

Rigorous bed rest (RBR) induces significant electrolyte changes, but little it is not known about the effect of acute bed rest (ABR) (i.e., abrupt confinement to a RBR). The aim of this study was to measure urinary and plasma electrolyte changes during ABR and RBR conditions. The studies were done during 3 d of a pre-bed-rest (BR) period and during 7 d of an ABR and RBR period. Thirty male trained athletes aged, 24.4 +/- 6.6 yr were chosen as subjects. They were divided equally into three groups: unrestricted ambulatory control subjects (UACS), acute-bed-rested subjects (ABRS), and rigorous-bed-rested subjects (RBRS). The UACS group experienced no changes in professional training and daily activities. The ABRS were submitted abruptly to a RBR regimen and without having any prior knowledge of the exact date and time when they would be subjected to an RBR regimen. The RBRS were subjected to an RBR regime on a predetermined date and time known to them from the beginning of the study. Sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), and phosphate (P) in plasma and urine, plasma renin activity (PRA) and plasma aldosterone (PA), physical characteristics, peak oxygen uptake, and food and water intakes were measured. Urinary Na, K, Ca, Mg, and P excretion and plasma Na, K, Mg, Ca, and P concentration, PRA, and PA concentration increased significantly (p < or = 0.01), whereas body weight, peak oxygen uptake, and food and water intakes decreased significantly in the ABRS and RBRS groups when compared with the UACS group. However, urinary and plasma Na, K, Mg, P, and Ca, PRA, and PA values increased much faster and were much greater in the ABRS group than in the RBRS group. Plasma and urinary Na, K, Ca, Mg, and P, PRA and PA levels, food and water intakes, body weight, and peak oxygen uptake did not change significantly in the UACS group when compared with its baseline control values. It was shown that RBR and ABR conditions induce significant increases in urinary and plasma electrolytes; however, urinary and plasma electrolyte changes appeared much faster and were much greater in the ABRS group than the RBRS group. It was concluded that the more abruptly motor activity is ended, the faster and the greater the urinary and plasma electrolyte change.

Adult↗