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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Isokinetic exercise: A review of the literature

Isokinetic muscle training has all the advantages of isometrics and isotonics while minimizing their deficiencies. By holding the speed of movement constant throughout the full range of motion, isokinetic training devices respond with increased resistance rather than acceleration when the power output of the muscle is increased. Isokinetic training is superior to isometric and isotonic training with respect to increases in strength, specificity of training, desirable changes in motor performance tasks, lack of muscle soreness, and decreases in relative body fat.

Olree, H. D.↗
NASA NTRS1979

Influence of hypokinesis on physiological functions in fowl

The effects of hypokinesis and postincubation stress (which are characteristic for modern techniques of poultry cage keeping) on the endocrine functions, metabolic reactions, body weight growth and proteosynthesis in the muscle of cocks was investigated. The stress due to hypokinesis was observed in growing cocks housed in metallic cages in which they could hardly turn around. The findings obtained indicate that a 35-day hypokinesis did not exert any more significant influence both on physiological functions and body weight growth as well as on proteosynthesis in the muscle of cocks under study; however, it speeded up the protein metabolism in the muscle. The postincubation stress modified significantly the hypokinesis effect. Findings recorded in birds differed considerably from findings obtained in laboratory mammals, in which the hypokinesis induced significant changes in endocrine functions, body weight decrease and proteosynthesis disorders. A good tolerance of hypokinesis by fowl can be interpreted not only by the phylogenetic remoteness of the compared species but also by the domestication.

Nvota, J.↗
NASA NTRS1980

Antibodies to myofibril antigens in cosmonauts after spaceflights

Serum samples obtained from 15 astronauts before and after spaceflights were studied with the use of the indirect immunofluorescent method. In seven astronauts antibodies to different elements of the human heart muscle appeared after flights. Strong and very strong luminescence of the elements of heart muscle tissue was detected in the astronauts after the third space flight. In a study of the sera on sections of bovine heart muscle tissue the reactions of the sera taken before and after flight were found to show no essential differences.

Tashpulatov, R. Y.↗
NASA NTRS1982

Suspension restraint - Induced hypokinesia and antiorthostasis as a simulation of weightlessness

Muscle, renal, fluid and electrolyte responses were measured in suspended rats; the hind limbs are non-load bearing and the front limbs can be used for feeding and grooming. Hind limb hypokinesia reverses after removal from the suspension harness. This suspension system is adjustable for a head-down tilt to produce antiorthostatic responses which are also reversible. Responses to hypokinesia or antiorthostatic hypokinesia for up to 14 days were measured, e.g., muscle atrophy: soleus greater than gastrocnemius equals plantaris greater than extensor digitorum longus, kaliuresis, and increased excretion of urea, NH3, and 3 methylhistidine. Muscle protein loss, a response to a reduction in RNA, is also reversible. A head-down tilt for 7-14 days results in diuresis and natriuresis. These changes are reversed within 24 hours after removal from the restraint harness. Physiological effects of suspension restraint can be used to simulate and predict responses to microgravity exposure.

Musacchia, X. J.↗
NASA NTRS1982

Fluid shifts in vascular and extravascular compartments of humans during and after simulated weightlessness

A study is presented of the transcapillary pressures and the possible fluid shifts in muscles and subcutaneous tissue of the lower leg before, during, and after head-down tilt. Results showed that the subjects experienced facial edema, headache, nasal congestion, diuresis, and decreased lower-leg volume in response to 8 hours of 5 degree head-down tilt. Also found were significant decreases in systolic and diastolic pressures 2 hours after initiation of tilt, although blood pressure normalized thereafter. The lower-leg volume, urine output and interstitial fluid pressures of the tibialis anterior muscle and overlying subcutaneous tissue also changed significantly. No significant change was found in the colloid osmotic pressures of blood or interstitial fluid. It is concluded that these results indicate the need for countermeasures to maintain precapillary-muscle tone during long space flights in order to prevent swelling of lower-leg tissues upon readjustment to earth's gravity.

Hargens, A. R.↗
NASA NTRS1983

Handgrip and general muscular strength and endurance during prolonged bedrest with isometric and isotonic leg exercise training

Measurements of maximal grip strength and endurance at 40 percent max strength were obtained for 7 men 19-21 years of age, 1-2 days before and on the first recovery day during three 2-week bedrest (BR) periods, each separated by a 3-week ambulatory recovery period. The subjects performed isometric exercise (IME) for 1 hr/day, isotonic exercise (ITE) for 1 hr/day, and no exercise (NOE) in the three BR periods. It was found that the mean maximal grip strength was unchanged after all three BR periods. Mean grip endurance was found to be unchanged after IME and ITE training, but was significantly reduced after NOE. These results indicate that IME and ITE training during BR do not increase or decrease maximal grip strength, alghough they prevent loss of grip endurance, while the maximal strength of all other major muscle groups decreases in proportion to the length of BR to 70 days. The maximal strength reduction of the large muscle groups was found to be about twice that of the small muscle groups during BR. In addition, it is shown that changes in maximal strength after spaceflight, BR, or water immersion deconditioning cannot be predicted from changes in submaximal or maximal oxygen uptake values.

Greenleaf, J. E.↗
NASA NTRS1984

Effects of suspension on tissue levels of glucocorticoid receptors

Differential muscle responses can be simulated by hypokinetic/hypodynamic (H/H) suspension of rats with complete unloading of the hindlimb muscles. Since mechanism(s) underlying these atrophic effects were not clearly elucidated, experiments were initiated to investigate a possible role for glucocorticoids in the physiological and biochemical responses to H/H. The principal objective was to assess the potential for alterations in peripheral responsiveness to glucocorticoids in response to H/H. Studies have initially focused on the determination of tissue levels of glucocorticoid receptors as one index of hormonal sensitivity at the cellular level. Four hindlimb muscles (soleus, gastrocnemius, plantaris and EDL), previously demonstrated to exhibit differential responses to H/H, were investigated. Receptor levels in other glucocorticoid sensitive tissues (heart, liver, and kidney) were determined. Male rats (180-200g) were suspended for 7 or 14 days, sacrificed by cervical dislocation, and the tissues excised.

Steffen, J. M.↗
NASA NTRS1985

Hyper-G stress-induced hyperglycemia in rats mediated by glucoregulatory hormones

The present investigation is concerned with possible relations of the hyperglycemic response of rats exposed to hyper-G stress to (1) alterations in blood levels of the glucoregulatory hormones and gluconeogenic substrates, and (2) changes in insulin response on muscle glucose uptake. Male Sprague-Dawley rats weighing 250-300 g were used in the study. The results of the experiments indicate that the initial rapid rise in blood glucose of rats exposed to hyper-G stress is mediated by increases in circulating catecholamines and glucagon, both potent stimulators of hepatic gluconeogenesis. Lactate, derived from epinephrine stimulation of muscle glycogenolysis, appears to be a major precursor for the initial rise in blood glucose. The inhibition of the insulin-stimulated glucose uptake by muscle tissues may be a factor in the observed sustained hyperglycemia.

Daligcon, B. C.↗
NASA NTRS1987

Possible role of brain stem respiratory neurons in mediating vomiting during space motion sickness

The object of this study was to determine if brain stem expiratory neurons control abdominal muscle activity during vomiting. The activity of 27 ventral respiratory group expiratory neurons, which are known to be of primary importance for control of abdominal muscle activity during respiration, was recorded. It is concluded that abdominal muscle activity during vomiting must be controlled not only by some brain stem expiratory neurons but also by other input(s).

Miller, A. D.↗
NASA NTRS1988

Comparative morphometry of fibers and capillaries in soleus following weightlessness (SL-3) and suspension

This work is a continuation of efforts to assess responses of rat skeletal muscle to weightlessness (W) and earthside laboratory experiments with unloading of hind limbs. The soleus is a slow-twitch, load-bearing (antigravity) muscle. Both exposure to W and to the hypokinesia/hypodynamia of whole-body suspension (WBS) results in soleus atrophy. Cross-sectional areas of both slow- and fast-twitch fibers decrease during 7 days of W or 7 or 14 days of WBS. Density and area changes tended to reverse to control levels during 7 days of recovery (R) following WBS. Capillary density was increased with 7 days of W or 7 or 14 days of WBS. During 7 days of R the capillary density returned toward control levels. In summary, the reduction in fiber cross-sectional areas and the increase in fiber and capillary densities support the hypothesis that in both W and WBS there is a loss in soleus muscle cell mass and not in fiber numbers.

Musacchia, X. J.↗
NASA NTRS1988

Diagnosis by integrating model-based reasoning with knowledge-based reasoning

Our research investigates how observations can be categorized by integrating a qualitative physical model with experiential knowledge. Our domain is diagnosis of pathologic gait in humans, in which the observations are the gait motions, muscle activity during gait, and physical exam data, and the diagnostic hypotheses are the potential muscle weaknesses, muscle mistimings, and joint restrictions. Patients with underlying neurological disorders typically have several malfunctions. Among the problems that need to be faced are: the ambiguity of the observations, the ambiguity of the qualitative physical model, correspondence of the observations and hypotheses to the qualitative physical model, the inherent uncertainty of experiential knowledge, and the combinatorics involved in forming composite hypotheses. Our system divides the work so that the knowledge-based reasoning suggests which hypotheses appear more likely than others, the qualitative physical model is used to determine which hypotheses explain which observations, and another process combines these functionalities to construct a composite hypothesis based on explanatory power and plausibility. We speculate that the reasoning architecture of our system is generally applicable to complex domains in which a less-than-perfect physical model and less-than-perfect experiential knowledge need to be combined to perform diagnosis.

Bylander, Tom↗
NASA NTRS1989

Exercise effects on the size and metabolic properties of soleus fibers in hindlimb-suspended rats

The effects of four-week-long hind-limb suspension (HS) of rats on the size the soleus muscle fibers and the activity of succinate dehydrogenase (SDH) in dark and light ATPase fibers were investigated together with the efficacy of an endurance exercise (EX) program (daily treadmill exercise for 1.5 h/day at 20 m/min and a 30-percent grade) in ameliorating HS-induced changes. It was found that, in comparison to age-matched controls, the soleus wet weight decreased by 69 and 30 percent in HS and HS-EX rats, respectively, and the percent of dark ATPase fibers increased from 10 percent in controls to 19 and 17 percent, respectively. The values of the integrated fiber activity (activity/min times muscle area) showed a net loss of SDH in both the light and dark ATPase fibers of HS rats, but only in the light ATPase fibers of the HS-EX rats, indicating that exercise ameliorated but did not prevent the muscle fiber atrophy induced by HS.

Graham, Scot C.↗
NASA NTRS1989

Changes in size and compliance of the calf after 30 days of simulated microgravity

The hypothesis that reducing muscle compartment by a long-term exposure to microgravity would cause increased leg venous compliance was tested in eight men who were assessed for vascular compliance and for serial circumferences of the calf before and after 30 days of continuous 6-deg head-down bed rest. It was found that head-down bed rest caused decreases in the calculated calf volume and the calf-muscle compartment, as well as increases in calf compliance. The percent increases in calf compliance correlated significantly with decreases in calf muscle compartment.

Convertino, Victor A.↗
NASA NTRS1990

Mathematical Model Of Nerve/Muscle Interaction

Phasic Excitation/Activation (PEA) mathematical model simulates short-term nonlinear dynamics of activation and control of muscle by nerve. Includes electronic and mechanical elements. Is homeomorphic at level of its three major building blocks, which represent motoneuron, dynamics of activation of muscle, and mechanics of muscle.

Hannaford, Blake↗
NASA NTRS1989

Cardiovascular, renal, electrolyte, and hormonal changes in man during gravitational stress, weightlessness, and simulated weightlessness: Lower body positive pressure applied by the antigravity suit

Because of their erect posture, humans are more vulnerable to gravitational changes than any other animal. During standing or walking man must constantly use his antigravity muscles and his two columns, his legs, to balance against the force of gravity. At the same time, blood is surging downward to the dependent portions of the body, draining blood away from the brain and heart, and requiring a series of complex cardiovascular adjustments to maintain the human in a bipedal position. It was not until 12 April 1961, when Yuri Gagarin became the first human being to orbit Earth, that we could confirm man's ability to maintain vital functions in space -- at least for 90 min. Nevertheless, man's adaptation to weightlessness entails the deconditioning of various organs in the body. Muscles atrophy, and calcium loss leads to loss of bone strength as the demands on the musculoskeletal system are almost nonexistent in weightlessness. Because of the lack of hydrostatic pressures in space, blood rushes to the upper portions of the body, initiating a complex series of cardioregulatory responses. Deconditioning during spaceflight, however, first becomes a potentially serious problem in humans returning to Earth, when the cardiovascular system, muscles and bones are suddenly exposed to the demanding counterforce of gravity -- weight. One of the main purposes of our studies was to test the feasibility of using Lower Body Positive Pressure, applied with an antigravity suit, as a new and alternative technique to bed rest and water immersion for studying cardioregulatory, renal, electrolyte, and hormonal changes in humans. The results suggest that Lower Body Positive Pressure can be used as an analog of microgravity-induced physiological responses in humans.

Kravik, Stein E.↗
NASA NTRS1989

Work, exercise, and space flight. 2: Modification of adaptation by exercise (exercise prescription)

The fundamentals of exercise theory on earth must be rigorously understood and applied to prevent adaptation to long periods of weightlessness. Locomotor activity, not weight, determines the capacity or condition of the largest muscles and bones in the body and usually also determines cardio-respiratory capacity. Absence of this activity results in rapid atrophy of muscle, bone, and cardio-respiratory capacity. Upper body muscle and bone are less affected depending upon the individual's usual, or 1-g, activities. Methodology is available to prevent these changes but space operations demand that it be done in the most efficient fashion, i.e., shortest time. At this point in time we can reasonably select the type of exercise and methods of obtaining it, but additional work in 1-g will be required to optimize the time.

Thornton, William↗
NASA NTRS1989

Cardiovascular group

As a starting point, the group defined a primary goal of maintaining in flight a level of systemic oxygen transport capacity comparable to each individual's preflight upright baseline. The goal of maintaining capacity at preflight levels would seem to be a reasonable objective for several different reasons, including the maintenance of good health in general and the preservation of sufficient cardiovascular reserve capacity to meet operational demands. It is also important not to introduce confounding variables in whatever other physiological studies are being performed. A change in the level of fitness is likely to be a significant confounding variable in the study of many organ systems. The principal component of the in-flight cardiovascular exercise program should be large-muscle activity such as treadmill exercise. It is desirable that at least one session per week be monitored to assure maintenance of proper functional levels and to provide guidance for any adjustments of the exercise prescription. Appropriate measurements include evaluation of the heart-rate/workload or the heart-rate/oxygen-uptake relationship. Respiratory gas analysis is helpful by providing better opportunities to document relative workload levels from analysis of the interrelationships among VO2, VCO2, and ventilation. The committee felt that there is no clear evidence that any particular in-flight exercise regimen is protective against orthostatic hypotension during the early readaptation phase. Some group members suggested that maintenance of the lower body muscle mass and muscle tone may be helpful. There is also evidence that late in-flight interventions to reexpand blood volume to preflight levels are helpful in preventing or minimizing postflight orthostatic hypotension.

Blomqvist, Gunnar↗
NASA NTRS1991

Importance of eccentric actions in performance adaptations to resistance training

The importance of eccentric (ecc) muscle actions in resistance training for the maintenance of muscle strength and mass in hypogravity was investigated in experiments in which human subjects, divided into three groups, were asked to perform four-five sets of 6 to 12 repetitions (rep) per set of three leg press and leg extension exercises, 2 days each weeks for 19 weeks. One group, labeled 'con', performed each rep with only concentric (con) actions, while group con/ecc with performed each rep with only ecc actions; the third group, con/con, performed twice as many sets with only con actions. Control subjects did not train. It was found that resistance training wih both con and ecc actions induced greater increases in muscle strength than did training with only con actions.

Dudley, Gary A.↗