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Nazar, K.

Publications and source records attributed to Nazar, K..

16 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Effects of 3-day bed rest on physiological responses to graded exercise in athletes 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 3-day BR. Before and after BR they performed incremental exercise test until volitional exhaustion. Respiratory gas exchange and heart rate (HR) were recorded continuously, and stroke volume (SV) was measured at submaximal loads. Blood was taken for lactate concentration ([LA]), epinephrine concentration ([Epi]), norepinephrine concentration ([NE]), plasma renin activity (PRA), human growth hormone concentration ([hGH]), testosterone, and cortisol determination. Reduction of peak oxygen uptake (VO(2 peak)) after BR was greater in the endurance athletes than in the remaining groups (17 vs. 10%). Decrements in VO(2 peak) correlated positively with the initial values (r = 0.73, P < 0.001). Resting and exercise respiratory exchange ratios were increased in athletes. Cardiac output was unchanged by BR in all groups, but exercise HR was increased and SV diminished in the sedentary subjects. The submaximal [LA] and [LA] thresholds were decreased in the endurance athletes from 71 to 60% VO(2 peak) (P < 0.001); they also had an earlier increase in [NE], an attenuated increase in [hGH], and accentuated PRA and cortisol elevations during exercise. These effects were insignificant in the remaining subjects. In conclusion, reduction of exercise performance and modifications in neurohormonal response to exercise after BR depend on the previous level and mode of physical training, being the most pronounced in the endurance athletes.

NASA Center ARC↗
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 NTRS2000

Body Temperatures During Exercise in Deconditioned Dogs: Effect of NACL and Glucose Infusion

Infusion of glucose (Glu) into normal exercising dogs attenuates the rise in rectal temperature (Delta-Tre) when compared with delta-Tre during FFA infusion or no infusion. Rates of rise and delta-=Tre levels are higher during exercise after confinement. Therefore, the purpose of this study was to determine if Glu infusion would attenuate the exercise-induced excess hyperthermia after deconditioning. Rectal and quadricep femoris muscle temperatures (Tmu) were measured in 7 male, mongrel dogs dogs (19.6 +/- SD 3.0 kg) during 90 minutes of treadmill exercise (3.1 +/-SD 0.2 W/kg) with infusion (30ml/min/kg) of 40% Glu or 0.9% NaCL before BC) and after confinement (AC) in cages (40 x 110 x 80 cm) for 8 wk. Mean (+/-SE body wt. were 19.6 +/- 1.1 kg BC and 19.5 +/- 1.1kg AC, exercise VO2 were not different (40.0 - 42.0 mi/min/kg-1). With NaCl AC, NaCl BC, GluAC, and GluBC: Delta-Tre were, 1.8, 1.4, 1.3 and 0.9C respectively; and Delta-Tmu were 2.3, 1.9, 1.6, and 1.4C. respectively (P<0.05 from GluBC). Compared with NaCl infusion, attenuated both Delta-Tre and Delta-Tmu BC and AC, respectively. Compared with GluBC, GluAC attenuated Delta-Tmu but not Delta-Tre. Thus. with similar heat production, the mechanism for attenuation at bad body temperature with Glu infusion must affect avenues of heat dissipation.

Greenleaf, J. E.↗
NASA NTRS1996

Effects of three day bed-rest on circulatory, metabolic and hormonal responses to oral glucose load in endurance trained athletes and untrained subjects

Endurance trained long distance runners and untrained individuals underwent three days of bed rest and oral glucose loading. Before and after bed rest, individuals were given glucose tolerance tests, and their heart rates, blood pressure, blood glucose levels, insulin levels, and catecholamine interactions were measured. Results indicated that glucose tolerance is more affected by bed rest-induced deconditioning in untrained individuals than in trained individuals.

NASA Discipline Regulatory Physiology↗
NASA NTRS1996

Effect of three day bed-rest on circulatory and hormonal responses to active orthostatic test in endurance trained athletes and untrained subjects

Circulatory and hormonal parameters were measured in endurance-trained athletes and control subjects during orthostatic tolerance tests conducted prior to and after three days of bed rest. Heart rate and blood pressure changes due to bed rest appeared to be the same in both groups. Hormonal changes, however, were different between the two groups, with the athletes having decreased sympathoadrenal activity and increased plasma renin activity. Untrained subjects had changes in cortisol secretion only.

NASA Center ARC↗
NASA NTRS1995

Glucose Infusion into Exercising Dogs after Confinement: Rectal and Active Muscle Temperatures

Intravenous glucose infusion into ambulatory dogs results in attenuation of exercise-induced increase of both rectal and thigh muscle temperatures. That glucose (Glu) infusion attenuates excessive increase in body temperature from restricted activity during confinement deconditioning. Intravenous glucose infusion attenuates the rise in exercise core temperature in deconditioned dogs by a yet undefined mechanism.

Greenleaf, J. E.↗
NASA NTRS1993

Muscle mitochondrial density after exhaustive exercise in dogs - Prolonged restricted activity and retraining

The effect of exhaustive treadmill exercise on mitochondrial density (MD) and ultrastructural changes in quadriceps femoris muscle was studied in 7 normal, healthy, male mongrel dogs before and after restricted activity (RA) and following a subsequent 2-month exercise retraining period. Mean time to exhaustion in the 2-month group decreased from 177 +/- 11 min before to 90 +/- 16 min after RA; retraining increased tolerance to 219 +/- 36 min above the pre-RA and 143 percent above the post-RA time. Post-RA exhaustion time in the 5-months group was 25 and 45 min. Muscle samples taken after RA showed abnormalities indicative of degeneration, which were reversed by retraining. Resting MD decreased from a control level of 27.8 percent to 14.7 percent and 16.3 percent, and was restored to 27.1 percent after retraining. Exhaustive exercise caused an increase in MD under control conditions and after RA, but not following retraining. Disruption of mitochondria after exercise was evident after 5-month confinement. Factors causing mitochondrial changes and eventually their disruption during exercise after restricted activity are not related as much to the state of fatigue as to the pre-exercise quality of the muscle modified by disease or training.

Nazar, K.↗
NASA NTRS1992

Exercise performance, core temperature, and metabolism after prolonged restricted activity and retraining in dogs

Physiological effects of restricted activity (RA) and subsequent retraining have been studied. Ten male mongrel dogs performed a submaximal exercise endurance test on a treadmill during kennel control, after 8 weeks of cage confinement and after eight weeks of retraining using the same treadmill protocol 1 h/d for 6 d/week. Data obtained show that RA reduces exercise endurance, the effectiveness of exercise thermoregulation, muscle glycogen stores, and the lipolytic response to exercise and to noradrenaline stimulation.

Nazar, K.↗
NASA NTRS1991

Muscle ultrastructural changes from exhaustive exercise performed after prolonged restricted activity and retraining in dogs

The effect of exhaustive treadmill exercise on ultrastructural changes in the quadriceps femoris muscle was studied in 7 normal, healthy dogs, before and after restricted activity (RA), and following a subsequent 2 month treadmill exercise retraining period for the 5 mo group. Mean time to exhaustion in the 2 mo group decreased from 177 + or - 22 min before to 90 + or - 32 min after RA. Retraining increased tolerance to 219 + or - 73 min; 24 pct. above the before RA and 143 pct. above the after RA time. After RA exhaustion time in the 5 mo group was 25 and 45 min. Before RA, pre-exercise muscle structure was normal and post exercise there was only slight swelling of mitochondria. After RA, pre-exercise, numerous glycogen granules and lipid droplets appeared in the muscle fibers, mitochondria were smaller, and sarcoplasmic reticulum channels widened; post exercise these changes were accentuated and some areas were devoid of glycogen, and there was fiber degradation. After 5 mo RA pre-exercise there were more pronounced changes; mitochondria were very small and dense, there were many lipid droplets, myofibrils were often separated, and the fibers appeared edematous and degenerating; post exercise the sarcoplasmic reticulum was swollen, no glycogen was present, and there was marked swelling and deformation of mitochondria. After retraining, both pre-exercise and post exercise there was still evidence of fiber degeneration. Thus, susceptibility of active skeletal muscle structures and subcellular elements, e.g., mitochondria, to the action of damaging factors occurring during exhaustive exercise is enhanced considerably by prolonged disuse.

Nazar, K.↗
NASA NTRS1985

Hypothalamic, rectal, and muscle temperatures in exercising dogs - Effect of cooling

An experimental investigation of the mechanisms of performance prolongation during exercise is presented. Measurements were obtained of the rectal, muscle, and hypothalamic temperature of dogs during treadmill exercise at an ambient temperature of 22 + or - 1 C, with and without cooling by use of ice packs. In comparison with exercise without cooling, exercise with cooling was found to: (1) increase exercise duration from 90 + or - 14 to 145 + or - 15 min; (2) attenuate increases in hypothalamic, rectal and muscle temperature; (3) decrease respiratory and heart rates; and (4) lower blood lactic acid content. It is shown that although significant differences were found between the brain, core, and muscle temperatures during exercise with and without cooling, an inverse relation was observed between muscle temperature and the total duration of exercise. It is suggested that sustained muscle hyperthermia may have contributed to the limitation of working ability in exercise with and without cooling.

Kruk, B.↗
NASA NTRS1980

Extracellular hyperosmolality and body temperature during physical exercise in dogs

The purpose of this study was to test the hypothesis that thermoregulation during exercise can be affected by extracellular fluid hyperosmolality without changing the plasma Na(+) concentration. The effects of preexercise venous infusions of hypertonic mannitol and NaCl solutions on rectal temperature responses were compared in dogs running at moderate intensity for 60 min on a treadmill. Plasma Na(+) concentration was increased by 12 meq after NaCl infusion, and decreased by 9 meq after mannitol infusion. Both infusions increased plasma by 15 mosmol/kg. After both infusions, rectal temperature was essentially constant during 60 min rest. However, compared with the noninfusion exercise increase in osmolality of 1.3 C, rectal temperature increased by 1.9 C after both postinfusion exercise experiments. It was concluded that inducing extracellular hyperosmolality, without elevating plasma, can induce excessive increases in rectal temperature during exericse but not at rest.

Kozlowski, S.↗
NASA NTRS1975

Temperature responses to infusion of electrolytes during exercise

To gain more insight into the ion-osmotic influence on temperature regulation, the rectal temperature responses of mongrel dogs were measured during one hour of treadmill-running at 1.2 m/sec up a 12 deg slope. Results indicate that as in man, the rise in body temperature during exercise appears to be a regulated process. There is a direct relationship between the rise and equilibrium levels of rectal temperature and the plasma sodium and osmotic concentrations. It remains to be determined if the hypernatremic-osmolality inhibits peripheral blood flow, the panting, salivation response, or both. Some background on previous experiments on resting and exercising dogs and men is recounted.

Greenleaf, J. E.↗
NASA NTRS1975

Temperature responses to infusion of electrolytes during exercise

Past studies on the influence of various metal ions on heat regulation in mammals are reviewed, and results of a study on the effect of Na and citrate in isotonic and hypertonic concentrations on temperature elevation during exercise in dogs are presented. Hypertonic administration of Na before or during treadmill running and dosis of citrate during treadmill running significantly raised core temperature over controls and isotonic cases. Thus the higher the plasma Na-osmotic concentration, the greater the inhibition of heat dissipation.

Greenleaf, J. E.↗
NASA NTRS1974

Temperature responses of exercizing dogs to infusion of electrolytes

The effect of infusions with solutions of various ionic and osmotic composition on exercise temperature responses was studied in dogs who do not regulate their temperature by sweating. The results suggest an association between plasma Na+ and Ca++ level within the normal physiological range and the control of body temperature during exercise.

Greenleaf, J. E.↗