Nutritional Needs in Cold and High-Altitude Environments Applications for Military Personnel in Field Operations (1996) / Chapter Skim
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17 Physical Performance at High Altitudes
17 Physical Performance at High Altitudes
Pages 319-330
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From page 319... ...
In fact, at extreme altitudes, deterioration occurs that may be complicated by psychological and cognitive impairment (Hornbein et al., 1989~. Even at moderate altitudes, factors that impair exercise may be confounded by concomitant maladaptation or altitude illness (see Anand arid Chandrashekhar, Chapter 18 in this volume)
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FIGURE 17-1 Data taken from two expeditions to high altitudes showing Me decrease in maximal oxygen consumption that occurs with a decrease in inspired partial pressure of oxygen as ogle ascends to high altitudes.
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From page 321... ...
Almost everyone, however, if they allow enough time for adaptation, will experience an adequate degree of ventilatory augmentation such that altitude illnesses are not experienced. At extreme altitudes, a brisk HVR and subsequent ventilatory response at rest and during exercise convey an advantage in physical performance (Schoene et al., 1984~.
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From page 322... ...
Minute ventilation during maximal exercise increases as the partial pressure of inspired oxygen decreases until an extreme altitude is reached such that a very low work rate and subsequent decrease in ventilatory demand are achieved. Additionally, maximal heart rate decreases in acclimatized individuals.
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Cardiac Response Cardiac output increases upon acute ascent to high altitudes but then decreases to a level that is comparable to sea-level values for any given
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From page 324... ...
Myocardial function is wellpreserved, even at extreme altitudes and in spite of high pulmonary vascular resistance from HPVR and exercise (Groves et al., 1987; Reeves et al., 19879. Upon first ascent, the heart rate at set workloads is higher than at sea level.
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From page 325... ...
Data at very high simulated altitudes in a hypobaric chamber in Operation Everest II suggest that the low driving pressure for oxygen in the periphery imposes a predictable limitation that is greater the higher one goes (Wagner et al., 1987~. This finding is controversial because it is not clear what the minimal level of oxygen is that will allow diffusion of oxygen from hemoglobin, across the cell membrane into the cytoplasm, and into the mitochondria (Hochachka et al., 1983~.
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From page 326... ...
Using both electrically stimulated and voluntary muscle contractions of the ankle flexors, investigators from Operation Everest II, the simulated ascent of Mount Everest, found evidence of central fatigue (evidence of decreased necrologic signals from the central nervous system) as well as decreased transmission along the nerve fiber but preservation of function at the neuromuscular junction (Garner et al., 19901.
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From page 327... ...
1982 Capillary density of skeletal muscles in dogs exposed to simulated altitude.
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From page 328... ...
Wagner, and C.S. Houston 1989 Operation Everest II: Maximal oxygen uptake at extreme altitudes.
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From page 329... ...
Stolp, and H.A. Saltzman 1986 Pulmonary gas exchange in humans exercising at sea level and simulated altitude.
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From page 330... ...
Schoene, and R.M. Winslow 1983 Maximal exercise at extreme altitudes on Mount Everest.
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