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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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22 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Exercise and neuromodulators: choline and acetylcholine in marathon runners

Certain neurotransmitters (i.e., acetylcholine, catecholamines, and serotonin) are formed from dietary constituents (i.e., choline, tyrosine and tryptophan). Changing the consumption of these precursors alters release of their respective neurotransmitter products. The neurotransmitter acetylcholine is released from the neuromuscular junction and from brain. It is formed from choline, a common constituent in fish, liver, and eggs. Choline is also incorporated into cell membranes; membranes may likewise serve as an alternative choline source for acetylcholine synthesis. In trained athletes, running a 26 km marathon reduced plasma choline by approximately 40%, from 14.1 to 8.4 uM. Changes of similar magnitude have been shown to reduce acetylcholine release from the neuromuscular junction in vivo. Thus, the reductions in plasma choline associated with strenuous exercise may reduce acetylcholine release, and could thereby affect endurance or performance.

NASA Discipline Regulatory Physiology↗
NASA NTRS1992

Oxygen transport and cardiovascular function at extreme altitude: lessons from Operation Everest II

Operation Everest II was designed to examine the physiological responses to gradual decompression simulating an ascent of Mt Everest (8,848 m) to an inspired PO2 of 43 mmHg. The principal studies conducted were cardiovascular, respiratory, muscular-skeletal and metabolic responses to exercise. Eight healthy males aged 21-31 years began the "ascent" and six successfully reached the "summit", where their resting arterial blood gases were PO2 = 30 mmHg and PCO2 = 11 mmHg, pH = 7.56. Their maximal oxygen uptake decreased from 3.98 +/- 0.2 L/min at sea level to 1.17 +/- 0.08 L/min at PIO2 43 mmHg. The principal factors responsible for oxygen transport from the atmosphere to tissues were (1) Alveolar ventilation--a four fold increase. (2) Diffusion from the alveolus to end capillary blood--unchanged. (3) Cardiac function (assessed by hemodynamics, echocardiography and electrocardiography)--normal--although maximum cardiac output and heart rate were reduced. (4) Oxygen extraction--maximal with PvO2 14.8 +/- 1 mmHg. With increasing altitude maximal blood and muscle lactate progressively declined although at any submaximal intensity blood and muscle lactate was higher at higher altitudes.

Non-NASA Center↗
NASA NTRS1992

Human torque velocity adaptations to sprint, endurance, or combined modes of training

We had groups of athletes perform sprint and endurance run training independently or concurrently for 8 weeks to examine the voluntary in vivo mechanical responses to each type of training. Pre- and posttraining angle-specific peak torque during knee extension and flexion were determined at 0, 0.84, 1.65, 2.51, 3.35, 4.19, and 5.03 radian.sec-1 and normalized for lean body mass. Knee extension torque in the sprint-trained group increased across all test velocities, the endurance-trained group increased at 2.51, 3.34, 4.19, and 5.03 radian.sec-1, and the group performing the combined training showed no change at any velocity. Knee flexion torque of the sprint and combined groups decreased at 0.84, 1.65, and 2.51 radian.sec-1. Knee flexion torque in the sprint-trained group also decreased at 0 radian.sec-1 and in the combined group at 3.34 radian.sec-1. Knee flexion torque in the endurance-trained group showed no change at any velocity of contraction. Mean knee flexion:extension ratios across the test velocities significantly decreased in the sprint-trained group. Knee extension endurance during 30 seconds of maximal contractions significantly increased in all groups. Only the sprint-trained group showed a significant increase in endurance of the knee flexors. These data suggest that changes in the voluntary in vivo mechanical characteristics of knee extensor and flexor skeletal muscles are specific to the type of run training performed.

NASA Discipline Musculoskeletal↗
NASA NTRS1992

Effects of training on muscle O2 transport at VO2max

To quantify the relative contributions of convective and peripheral diffusive components of O2 transport to the increase in leg O2 uptake (VO2leg) at maximum O2 uptake (VO2max) after 9 wk of endurance training, 12 sedentary subjects (age 21.8 +/- 3.4 yr, VO2max 36.9 +/- 5.9 ml.min-1.kg-1) were studied. VO2max, leg blood flow (Qleg), and arterial and femoral venous PO2, and thus VO2leg, were measured while the subjects breathed room air, 15% O2, and 12% O2. The sequence of the three inspirates was balanced. After training, VO2max and VO2leg increased at each inspired O2 concentration [FIO2; mean over the 3 FIO2 values 25.2 +/- 17.8 and 36.5 +/- 33% (SD), respectively]. Before training, VO2leg and mean capillary PO2 were linearly related through the origin during hypoxia but not during room air breathing, suggesting that, at 21% O2, VO2max was not limited by O2 supply. After training, VO2leg and mean capillary PO2 at each FIO2 fell along a straight line with zero intercept, just as in athletes (Roca et al. J. Appl. Physiol. 67: 291-299, 1989). Calculated muscle O2 diffusing capacity (DO2) rose 34% while Qleg increased 19%. The relatively greater rise in DO2 increased the DO2/Qleg, which led to 9.9% greater O2 extraction. By numerical analysis, the increase in Qleg alone (constant DO2) would have raised VO2leg by 35 ml/min (mean), but that of DO2 (constant Qleg) would have increased VO2leg by 85 ml/min, more than twice as much. The sum of these individual effects (120 ml/min) was less (P = 0.013) than the observed rise of 164 ml/min (mean). This synergism (explained by the increase in DO2/Qleg) seems to be an important contribution to increases in VO2max with training.

NASA Discipline Musculoskeletal↗