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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Effects of Three-Day Bed Rest on Physiological Responses to Graded Exercise in Endurance Athletes, Body Builders and Sedentary Men

To test the hypotheses that short-term bed rest (BR) deconditioning influences metabolic, cardiorespiratory and neurohormonal responses to exercise and that these effects depend on the subjects' training status 12 sedentary men, and 10 endurance- and 10 strength-trained athletes were submitted to three-day BR. Before and after BR they performed incremental exercise test until volitional exhaustion. Respiratory gas exchange and HR were recorded continuously and stroke volume (SV) was measured at submaximal loads. Blood was taken for lactate [LA], adrenaline [A], noradrenaline, [NA], renting activity (PRA), growth hormone [hGH], testosterone and cortisol determination. Reduction of peak oxygen uptake (VO2peak) after BR was greater in the endurance athletes (than in the remaining groups (17 % vs. 100%). Decrements in VO2peak correlated positively with the initial values (r = 0.73, p less than 0.001). Resting and exercise respiratory exchange ratios were increased in athletes. Cardiac output was unchanged by BR in all groups, but exercise HR was increased and SV diminished in the sedentary subjects. The submaximal [LA] and [LA] thresholds were decreased the in endurance athletes from 71 to 60 %VO2 peak (p less than 0.001); they also had an earlier increase in [NA], and an attenuated increase in [hGH), and accentuated PRA and cortisol elevations during exercise. These effects were insignificant in the remaining subjects. In conclusion: reduction of exercise performance and modifications in neurohormonal response to exercise after BR depend on the previous level and mode of physical training, being the most pronounced in the endurance athletes.

Smorawinski, J.↗
NASA NTRS2001

Effects of Three-Day Bed Rest on Physiological Responses to Graded Exercise in Endurance Athletes, Body Builders and Sedentary Men

To test the hypotheses that short-term bed rest (BR) deconditioning influences metabolic, cardiorespiratory and neurohormonal responses to exercise and that these effects depend on the subjects' training status, 12 sedentary men, and 10 endurance- and 10 strength-trained athletes were submitted to three-day BR. Before and after BR they performed incremental exercise tests until volitional exhaustion. Respiratory gas exchange and HR were recorded continuously and stroke volume (SV) was measured at submaximal loads. Blood was taken for lactate [LA], adrenaline [A], noradrenaline [NA], renin activity (PRA), growth hormone [hGH], testosterone and cortisol determination. Reduction of peak oxygen uptake (V02peak) after BR was greater in the endurance athletes than in the remaining groups (17 % vs. 10%). Decrements in VO2peak correlated positively with the initial values (r = 0.73, p is less than 0.001). Resting and exercise respiratory exchange ratios were increased in athletes. Cardiac output was unchanged by BR in all groups, but exercise HR was increased and SV diminished in the sedentary subjects. The submaximal [LA] and [LA] thresholds were decreased the in endurance athletes from 71 to 60% V02 peak (p is less than0.001), they also had an earlier increase in [NA], an attenuated increase in [hGH], and accentuated PRA and cortisol elevations during exercise. These effects were insignificant in the remaining subjects. In conclusion: reduction of exercise performance and modifications in neurohormonal response to exercise after BR depend on the previous level and mode of physical training, being the most pronounced in the endurance athletes.

Smorawinski, J.↗
NASA NTRS2007

Effect of Head-Down Bed Rest and Artificial Gravity Countermeasure on Cardiac Autonomic and Advanced Electrocardiographic Function

To study the effects of 21 days of head-down bed rest (HDBR), with versus without an artificial gravity (AG) countermeasure, on cardiac autonomic and advanced electrocardiographic function. Fourteen healthy men participated in the study: seven experienced 21 days of HDBR alone ("HDBR controls") and seven the same degree and duration of HDBR but with approximately 1hr daily short-arm centrifugation as an AG countermeasure ("AG-treated"). Five minute supine high-fidelity 12-lead ECGs were obtained in all subjects: 1) 4 days before HDBR; 2) on the last day of HDBR; and 3) 7 days after HDBR. Besides conventional 12-lead ECG intervals and voltages, all of the following advanced ECG parameters were studied: 1) both stochastic (time and frequency domain) and deterministic heart rate variability (HRV); 2) beat-to-beat QT interval variability (QTV); 3) T-wave morphology, including signal-averaged T-wave residua (TWR) and principal component analysis ratios; 4) other SAECG-related parameters including high frequency QRS ECG and late potentials; and 5) several advanced ECG estimates of left ventricular (LV) mass. The most important results by repeated measures ANOVA were that: 1) Heart rates, Bazett-corrected QTc intervals, TWR, LF/HF power and the alpha 1 of HRV were significantly increased in both groups (i.e., by HDBR), but with no relevant HDBR*group differences; 2) All purely "vagally-mediated" parameters of HRV (e.g., RMSSD, HF power, Poincare SD1, etc.), PR intervals, and also several parameters of LV mass (Cornell and Sokolow-Lyon voltages, spatial ventricular activation times, ventricular gradients) were all significantly decreased in both groups (i.e., by HDBR), but again with no relevant HDBR*group differences); 3) All "generalized" or "vagal plus sympathetic" parameters of stochastic HRV (i.e., SDNN, total power, LF power) were significantly more decreased in the AG-treated group than in the HDBR-only group (i.e., here there was a relevant HDBR*group difference); and 4) QTV index was also significantly more changed (increased) in the AG-treated group than in the HDBR-only group, although this was clearly due to a greater decrease in generalized HRV and not to a greater increase in QTV proper because there was no relevant HDBR*group effect for either the SDNN or the RMSSD of QTV. Brief daily AG treatment by short-arm centrifuge during each of 21 days of HDBR does not appear to protect against HDBR-related losses of cardiac autonomic function or of LV mass as estimated by ECG.

Schlegel, T. T.↗
NASA NTRS2003

Recovery After Prolonged Bed-Rest Deconditioning

Recovery data were analyzed from normal healthy test subjects maintained in the horizontal or head-down body position in well-controlled bed rest (BR) studies in which adherence to the well-designed protocol was monitored. Because recovery data were almost always of secondary importance to the data collected during the BR period, there was little consistency in the recovery experimental designs regarding control factors (e.g., diet or exercise), duration, or timing of data collection. Thus, only about half of the BR studies that provided appropriate data were analyzed here. These recovery data were sorted into two groups: those from BR protocols of less than 37 days, and those from protocols greater than 36 days. There was great disparity in the unchanged responses at the end of BR in these two groups. Likewise with the variables that required more than 40 days for recovery; for example, some immune variables required more than 180 days. Knowledge of the recovery process after BR in healthy people should assist rehabilitation workers in differentiating "healthy" BR recovery responses from those of the infirmity of sick or injured patients; this should result in more appropriate and efficient health care.

Greenleaf, John E.↗
NASA NTRS2001

Influence of head-down bed rest on the circadian rhythms of hormones and electrolytes involved in hydroelectrolytic regulation

We investigated in six men the impact of a 17-day head-down bed rest (HDBR) on the circadian rhythms of the hormones and electrolytes involved in hydroelectrolytic regulation. This HDBR study was designed to mimic an actual spaceflight. Urine samples were collected at each voiding before, during and after HDBR. Urinary excretion of aldosterone, arginine vasopressin (AVP), cyclic guanosine monophosphate (cGMP), cortisol, electrolytes (Na+ and K+) and creatinine were determined. HDBR resulted in a significant reduction of body mass (P < 0.01) and of caloric intake [mean (SEM) 2,778 (37) kcal.24 h(-1) to 2,450 (36) kcal.24 h(-1), where 1 kcal.h(-1) = 1.163 J.s(-1); P< 0.01]. There was a significant increase in diastolic blood pressure [71.8 (0.7) mmHg vs 75.6 (0.91) mmHg], with no significant changes in either systolic blood pressure or heart rate. The nocturnal hormonal decrease of aldosterone was clearly evident only before and after HDBR, but the day/night difference did not appear during HDBR. The rhythm of K+ excretion was unchanged during HDBR, whereas for Na+ excretion, a large decrease was shown during the night as compared to the day. The circadian rhythm of cortisol persisted. These data suggest that exposure to a 17-day HDBR could induce an exaggeration of the amplitude of the Na+ rhythm and abolition of the aldosterone rhythm.

NASA Center ARC↗
NASA NTRS2014

Analysis of Arterial Mechanics During Head-down Tilt Bed Rest

Arterial health may be affected by microgravity or ground based analogs of spaceflight, as shown by an increase in thoracic aorta stiffness1. Head-down tilt bed rest (HDTBR) is often used as a ground-based simulation of spaceflight because it induces physiological changes similar to those that occur in space2, 3. This abstract details an analysis of arterial stiffness (a subclinical measure of atherosclerosis), the distensibility coefficient (DC), and the pressure-strain elastic modulus (PSE) of the arterial walls during HDTBR. This project may help determine how spaceflight differentially affects arterial function in the upper vs. lower body.

Elliot, Morgan↗
NASA NTRS2006

WISE-2005: LBNP/Treadmill and Resistive Exercise Countermeasures Maintain Aerobic Capacity during a 60-d Bed Rest

We have previously documented that supine treadmill exercise within lower body negative pressure (LBNPex) performed 6 sessions (raised dot) wk(sup -1) during 15- and 30-day bed rests (BR) maintained upright aerobic capacity (VO2pk). In the present study, ure are evaluating whether aerobic capacity is maintained during a 60-d BR when the LBNPex frequency is reduced to 2-4 sessions (raised dot) wk(sup -1) and resistance exercise (REX) is added 2-3 sessions (raised dot) wk(sup -1). Eight healthy women (32 plus or minus 4 yrs; 56.4 plus or minus 3.6 kg; 164 plus or minus 8 cm; mean plus or minus SD) performed maximal-exertion, graded treadmill tests before and 3 days after a 60-d, 6 deg. head-down tilt BR. (Earliest day the medical monitors would permit a maximal exercise test post-BR). During BR, four subjects performed no exercise (CON), while four other subjects (EX) performed LBNPex and REX on separate days. The LBNPex countermeasure employed an intermittent (40-80% pre-BR VO2pk), 40-min protocol against an LBNP pressure (-49 plus or minus 3 mmHg) applied to provide a footward force equivalent to 1.0-1.2 body weight. REX consisted of maximal concentric and eccentric supine leg press and heel raise exercises using a gravity-independent flywheel ergometer. Comparisons were performed using paired (within-group) or non-paired (between-group) t-tests. Three days post-BR, VO2pk of the CON group was reduced significantly from pre-BR (Pre:37.2 plus or minus 1.2, Post: 29.4 plus or minus 2 ml (raised dot) kg(sup -1) (raised dot) min(sup -1), P less than 0.05), while the VO2pk of the EX group was not significantly reduced (Pre: 39.6 plus or minus 1.9, Post: 38.0 plus or minus 0.6 ml (raised dot) kg(sup -1) (raised dot) min(sup -1)). Peak heart rate, ventilation, rating of perceived exertion, and respiratory exchange ratio were not significantly different between the two groups pre- and post-BR. These preliminary results suggest that the combined LBNPex and REX countermeasures may be sufficient to maintain upright aerobic capacity after long-duration space flights.

Schneider, Suzanne M.↗
NASA NTRS2001

Exercise Thermoregulation Following 13 Days of Bed Rest

This investigation examined two potential mechanisms, altered skin blood flow (SBF) and sweating rate (SR) responses, that may be responsible for an elevated core temperature during exercise after bed rest (BR) and space flight. Seven healthy men (29 +/- 5 yr, 179.6 +/- 7.1 cm, 77.2 +/- 17.0kg; mean +/- SD) underwent 13 days of 6 deg head-down BR. Pre- and post-BR, subjects completed supine submaximal cycle ergometry (20 min at 40% and 20 min at 65% of pre-BR supine VO2pk) in a thermoneutral room (23.4 +/- 0.5 C, 56 +/- 8 %RH) during, heat production (VO2 ; indirect calorimetry), intestinal temperature (T(sub in) ; ingestible pill), SBF (laser Doppler velocimetry), local SR (dew point hygrometry), and total sweat loss (TSL; Delta body weight) were measured. Pre- and post- BR plasma volume (PV) was measured using I-125 dilution. After BR, T(sub in) was elevated at rest (36.99 +/- 0.14 vs. 37.30 +/- 0.06 C; p<_0.05) and at the end of exercise (37.57 +/- 0.13 vs. 37.90 +/- 0.09 C; P less than or equal to 0.05). However, the increase in T(sub in) from rest to the end of exercise was not different after BR (0.59 +/- 0.07 vs. 0.60 +/- 0.07 C). There was no difference in VO2 pre- to post-BR during rest (0.28 +/- 0.04 vs. 0.24 +/- 0.03 1 multiplied by min(exp -1) ) or 40% VO2pk (0.95 +/- 0.08 vs. 0.96 +/- 0.05 1 multiplied by min(exp -1)), but VO2 was significantly less at the end of the 65% VO2pk stage (1.53 +/- 0.09 vs. 1.42 +/- 0.11 1 multiplies by min(exp - 1); p less than or equal to 0.05). The percent change in SBF from rest to end of exercise was less after BR (211 +/- 53 vs. 96 +/- 31%; p less than or equal to 0.05), the threshold for the onset of SBF was greater (37.17 +/- 0.18vs. 37.51 +/- 0.17 C; p less than or equal to 0.05), and the slope of the response tended to be reduced (536 +/- 184 vs. 201 +/- 46 %A PC; p=0.08). TSL was not different after BR (0.42+0.06 vs. 0.44 +/- 0.08 kg), but the T in threshold at the onset of sweating was delayed significantly (37.06 +/- 0.1 1 vs. 37.34 +/- 0.06 C; p less than or equal to 0.05). However, the slope of SR was not changed after BR (3.45 +/- 1.22 vs. 2.58 +/- 0.71 mg multiplied by min(exp -1) multiplied by cm sq). PV was decreased by 11% after BR (3,259 +/- 177 vs. 2,894 +/- 138 ml; p less than or equal to 0.05). These results suggest that exercise SBF and SR responses after BR are altered, and heat production is unchanged or reduced, consistent with observations following space flight. The higher resting T(sub in) with a proportional increase in T(sub in) during exercise and delayed onset of SBF and SR suggest a centrally-mediated elevation in the thermoregulatory set point during microgravity exposure.

Lee, Stuart M. C.↗
NASA NTRS1988

Changes in plasma volume during bed rest - Effects of menstrual cycle and estrogen administration

The effect of increased blood estrogen concentration, caused either during normal menstrual cycles or by exogenous administration of premarin, on the bed-rest (BR) induced decrease in plasma volume (PV) was investigated. In women who underwent duplicate 11-day BR without estrogen supplementation, the PV was found to decrease significantly, during the first 5 days of BR, to a lower level at which it remained for the rest of the BR period. In women who began BR in the periovulatory stage of the menstrual cycle, the loss of PV was delayed, while women who began BR during other stages of the cycle exhibited the usual trend of the PV decrease during the BR. In women who underwent a single 12-day BR period while taking premarin (1.25 mg/day), PV was found to decrease during the first 4-5 days of BR, but then returned toward the pre-BR level during the remainder of the BR, indicating that estrogens have a role in stabilizing body fluid volume.

Fortney, S. M.↗
NASA NTRS1994

Knee-Joint Proprioception During 30-Day 6 deg Head-Down Bed Rest with Isotonic and Isokinetic Exercise Training

To determine if daily isotonic exercise or isokinetic exercise training coupled with daily log proprioceptive training, would influence log proprioceptive tracking responses during Bed Rest (BR), 19 men (36 +/- SD 4 years, 178 +/- 7 cm, 76.8 +/- 7.8 kg) were allocated into a NO-Exercise (NOE) training control group (n = 5), and IsoTanic Exercise (ITE, n = 7) and IsoKinetic Exercise (IKE, n = 7) training groups. Exercise training was conducted during BR for two 30-min period / d, 5 d /week. Only the IKE group performed proprioceptive training using a now isokinetic procedure with each lower extremity for 2.5 min before and after the daily exercise training sessions; proprioceptive testing occurred weekly for all groups. There were no significant differences in proprioceptive tracking scores, expressed as a percentage of the perfect score of 100, in the pro-BR ambulatory control period between the three groups. Knee extension and flexion tracking responses were unchanged with NOE during BR, but were significantly greater (*p less than 0.05) at the end of BR in both exercise groups when compared with NOE responses (extension: NOE 80.7 +/- 0.7%, ITE 82.9 +/- 0.6%, IKE 86.5* +/- 0.7%; flexion: NOE 77.6 +/- 1.50, ITE 80.0 +/- 0.8% (NS), IKE 83.6* +/- 0.8%). Although proprioceptive tracking was unchanged during BR with NOE, both lsotonic exercise training (without additional propriaceptive training) and especially isokinetic exercise training when combined with daily proprioceptive training, significantly improved knee proprioceptive tracking responses after 30 d of BR.

Bernauer, E. M.↗
NASA NTRS1973

An evaluation of the effects of bed rest, sleep deprivation and discontinuance of training on the physical fitness of highly trained young men

This experiment was conducted to determine what physiological effects result when highly trained subjects are confined to bed, deprived of sleep, or allowed to discontinue training. Results indicated: (1) There was a moderate increase in strength variables due to the training in this experiment but the stress which the subjects received caused a negligible change in strength variables. (2) The training program resulted in highly significant changes in specific bicycle ergometer variables indicating good increases in cardiopulmonary fitness. Five days of bed rest or fifty hours of sleep deprivation caused comparable drastic decreases in cardiopulmonary fitness. Post stress the subjects reverted to a normal daily schedule and after two weeks they had recovered about half of what they lost. (3) Cardiac output remains relatively constant at a constant work load, but stroke volume increases with conditioning and decreases with deconditioning due to stress.

Olree, H. D.↗
NASA NTRS2002

Effect of 3-Day Bed Rest on the Basal Sympathetic Activity and Responsiveness of this System to Physiological Stimuli In Athletes and Sedentary Subjects

The aims of this study were: (1) to examine the effect of three days of bed rest (BR) on basal plasma epinephrine [E] and norepinephrine [NE] and the catecholamine responses to various physiological stimuli, and (2) to find out whether previous physical activity modifies effects of BR. In the first series, 29 young men (11 sedentary students, 8 endurance and 10 strength trained athletes) were submitted to oral glucose tolerance test in supine position and to active orthostatic test before and after 3 days of BR. Plasma [E] and [NE] were measured after overnight fast (basal condition), at 60, 120 and 180 min after glucose ingestion (70 a), and at the 8th min of unsupported standing. In the second series, other 22 subjects (12 sedentary students, 10 endurance and 10 strength trained athletes) were submitted to 2 min cold pressor test (CPT) and exercise. Plasma E and NE were determined in the supine position after overnight fast and at 60th and 120th s of hand cooling. Then, after breakfast followed by 2-3 hour sitting, the subjects performed cycle ergometer exercise with workload increasing until volitional exhaustion. Plasma [E] and [NE] were determined at the end of each load. Plasma catecholamines were determined made radioenzymatically. After BR, basal plasma [NE] was decreased in endurance and strength athletes (p<0.01) but not in sedentary subjects. In neither group BR affected the basal [E]. Responses of both catecholamines to glucose load were diminished after BR in all three groups (p<0.05) but the effect was most pronounced in the endurance athletes. All subjects tolerated well 8-min standing although their heart rate response was increased after BR. Plasma catecholamine responses standing were not significantly affected by BR in either group but the plasma [NE] and [E] during standing were lowered after BR in endurance athletes (p<0.01). BR did not affect blood pressure and catecholamine responses to CPT. The pre- and post-exercise plasma catecholamines were similar before and after BR although the subjects achieved lower maximal loads after BR. In endurance athletes the threshold for plasma NA rise occurred at lower work intensity after than before BR (p<0.05).

Smorawinski, Jerzy↗
NASA NTRS1993

Body fluid alterations during head-down bed rest in men at moderate altitude

To determine the effects of hypoxia on fluid balance responses to simulated zero-gravity, measurements were made in six subjects before and during -5 deg continuous head-down bed rest (HDBR) over 8 d at 10,678 ft. The same subjects were studied again at this altitude without HDBR as a control (CON) using a cross-over design. During this time, they maintained normal upright day-time activities, sleeping in the horizontal position at night. Fluid balance changes during HDBR in hypoxia were more pronounced than similar measurements previously reported from HDBR studies at sea level. Plasma volume loss was slightly greater and the diuresis and natriuresis were doubled in magnitude as compared to previous studies in normoxia and sustained for 4 d during hypoxia. These changes were associated with an immediate but transient rise in plasma atrial natriuretic peptide (ANP) to day 4 of 140 percent in HDBR and 41 percent in CON (p less than 0.005), followed by a decline towards baseline. Differences were less striking between HDBR and CON for plasma antidiuretic hormone and aldosterone, which were transiently reduced by HDBR. Plasma catecholamines showed a similar pattern to ANP in both HDBR and CON, suggesting that elevated ANP and catecholamines together accounted for the enhanced fluid shifts with HDBR during hypoxia.

Loeppky, J. A.↗
NASA NTRS2011

Muscle Adaptations Following Short-Duration Bed Rest with Integrated Resistance, Interval, and Aerobic Exercise

Unloading of the musculoskeletal system during space flight results in deconditioning that may impair mission-related task performance in astronauts. Exercise countermeasures have been frequently tested during bed rest (BR) and limb suspension; however, high-intensity, short-duration exercise prescriptions have not been fully explored. PURPOSE: To determine if a high intensity resistance, interval, and aerobic exercise program could protect against muscle atrophy and dysfunction when performed during short duration BR. METHODS: Nine subjects (1 female, 8 male) performed a combination of supine exercises during 2 weeks of horizontal BR. Resistance exercise (3 d / wk) consisted of squat, leg press, hamstring curl, and heel raise exercises (3 sets, 12 repetitions). Aerobic (6 d / wk) sessions alternated continuous (75% VO2 peak) and interval exercise (30 s, 2 min, and 4 min) and were completed on a supine cycle ergometer and vertical treadmill, respectively. Muscle volumes of the upper leg were calculated pre, mid, and post-BR using magnetic resonance imaging. Maximal isometric force (MIF), rate of force development (RFD), and peak power of the lower body extensors were measured twice before BR (averaged to represent pre) and once post BR. ANOVA with repeated measures and a priori planned contrasts were used to test for differences. RESULTS: There were no changes to quadriceps, hamstring, and adductor muscle volumes at mid and post BR time points compared to pre BR (Table 1). Peak power increased significantly from 1614 +/- 372 W to 1739 +/- 359 W post BR (+7.7%, p = 0.035). Neither MIF (pre: 1676 +/- 320 N vs. post: 1711 +/- 250 N, +2.1%, p = 0.333) nor RFD (pre: 7534 +/- 1265 N/ms vs. post: 6951 +/- 1241 N/ms, -7.7%, p = 0.136) were significantly impaired post BR.

Hackney, Kyle J.↗
NASA NTRS1994

Isokinetic Strength and Endurance During 30-day 6 deg Head-Down Bed Rest with Isotonic and Isokinetic Exercise Training

The purpose of our study was to determine if an intensive, intermittent, isokinetic, lower extremity exercise training program would attenuate or eliminate the decrease of muscular strength and endurance during prolonged bed rest (BR). The 19 male subjects (36 +/- 1 yr, 178 +/- 2 cm, 76.5 +/- 1.7 kg) were allocated into a no exercise (NOE) training group (N = 5), an isotonic (lower extremity cycle orgometer) exercise (ITE) training group (N = 7), and an isokinetic (isokinetic knee flexion-extension) exercise (IKE) training group (N = 7). Peak knee (flexion and extension) and shoulder (abduction-adduction) functions were measured weekly in all groups with one 5-repetition set. After BR, average knee extension total work decreased by 16% with NOE, increased by 27% with IKE, and was unchanged with ITE. Average knee flexion total work and peak torque (strength) responses were unchanged in all groups. Force production increased by 20% with IKE and was unchanged with NOE and ITE. Shoulder total work was unchanged in all groups, while gross average peak torque increased by 27% with ITE and by 22% with IKE, and was unchanged with NOE. Thus, while ITE training can maintain some isokinetic functions during BR, maximal intermittent IKE training can increase other functions above pre-BR control levels.

Greenleaf, J. E.↗