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PubMed2006

Effects of short-term acclimatization to altitude (3200 m) on aerobic and anaerobic exercise performance.

Aerobic exercise performance decreases upon ascent to altitude whereas anaerobic performance remains unchanged. Although the effects of 1 - 3 wk of altitude acclimatization on both aerobic and anaerobic exercise performance have been well studied, the effects of short-term altitude acclimatization (i.e., 45 h) on these parameters have not been well defined. Therefore, both aerobic and anaerobic exercise performance was evaluated in five healthy men (51.4 +/- 7.7 years, 175 +/- 4.2 cm, and 73.8 +/- 6.1 kg) at low altitude (LA, 600 m), upon acute exposure (approximately 1 - 3 h) to 3200 m (HA1) and on the third day of altitude exposure (HA3, 3200 m). Subjects performed three consecutive exercise tests, separated by approximately 1 - 3 h of rest, of various durations (i.e., 30 s, 5 min, and 50 min) on a cycle ergometer in each environmental condition. Anaerobic cycling performance (i. e., 30 s) was the same at LA, HA1, and HA3. Aerobic cycling performance (i. e., 5 min and 50 min) was reduced by 12.0 and 11.3 %, respectively, upon acute exposure to altitude. There was no change in the 5-min cycling performance but the 50-min cycling performance improved by 5.7 % from HA1 to HA3 which implies a 50 % recovery of the initial loss. These findings are important for individuals going to high altitude for work, for athletic competition, or recreation.

Adaptation, Physiological↗

PubMed1992

A practical approach to altitude training: where to live and train for optimal performance enhancement.

Altitude training may improve performance by a number of mechanisms. Acclimatization may improve both oxygen delivery and extraction. Hypoxic exercise may increase the training stimulus thus magnifying the effects of endurance training. Conversely, high altitude decreases VO2max and reduces the workloads at which training occurs. At altitude, base training is performed at a slower velocity and lower oxygen uptake (lower absolute workload) compared to sea level, though heart rate is similar and lactate is higher (probably greater relative workload). Interval workouts are performed at a lower absolute workload at altitude and are associated with lower peak heart rates and blood lactate concentrations. Red cell volume is increased during altitude training, as long as iron stores are normal. We suggest that for performance at altitude, acclimatization and/or hypoxic exercise is preferable; for performance at sea level, living at altitude (acclimatization) with sea level training may be the optimal strategy. However neither approach is a substitute for a carefully designed training program including appropriate rest and nutrition.

Acclimatization↗

PubMed1999

Effects of iron supplementation on total body hemoglobin during endurance training at moderate altitude.

The aim of the study was to test the hypothesis that iron supplementation in well-trained non-iron-depleted athletes leads to an enhanced increase of total body hemoglobin (TBH) during training at moderate altitude. Therefore, the members of the national German boxing team were randomly assigned to treatment with ferrous-glycine-sulfate (1335 mg equivalent to 200mg elementary iron daily) or with placebo during 18 days of endurance training at moderate altitude (1800 m). Before and after altitude training TBH was determined by CO-rebreathing, measures of exercise performance were determined with an incremental treadmill test. Before, during and after the stay at moderate altitude erythropoietin (Epo), reticulocytes (Retics) and parameters of iron metabolism were measured in venous blood. The results show that TBH did not change significantly in the placebo-group and even slightly, but significantly decreased in the iron-treated group. However, there was a significant increase of Epo and Retics in both groups during training at moderate altitude whereas parameters of iron metabolism remained unchanged. VO2max did not change either. To test whether a training-induced hemolysis, an increased urinary iron excretion or gastrointestinal blood loss could explain the unexpected drop of TBH we tested most of the boxers again during a similar training camp at low altitude (400-1000 m) to obtain measures of hemolysis, urinary iron excretion and occult hemoglobin loss with the stools. Although there were signs of an increased erythrocyte turnover no iron loss could be observed. We conclude that 18 days of endurance training at an altitude of 1800 m does not lead to an increase of TBH in non-iron-depleted athletes with and without iron supplementation.

Adult↗

PubMed1982

Effects of caffeine ingestion on exercise performance at low and high altitudes in cross-country skiers.

The effect of caffeine on exercise time over a specified distance (approx. 21 km) was investigated in well-trained cross-country skiers (14 subjects) both at low (300 m above sea level) and high (2900 m above sea level) altitudes. Each subject participated in two races at both altitudes--one after caffeine ingestion (6 mg/kg body weight) and one after placebo on a double-blind basis. In each race 50% of the participants were medicated with caffeine, thereby after normalization (where the mean time was set at 100%), when the influence of weather and snow conditions were minimized, the difference between the race time with caffeine and placebo could be calculated for each individual and expressed as a percentage of the mean. At low altitudes, after half the distance, the race time with caffeine was decreased 0.94% of the mean time (corresponding to approx. 33 s) as compared to placebo (P less than 0.05), whereas after the full distance the corresponding decrease was 1.7% of the mean time (corresponding to approx. 59 s) (0.05 less than P less than 0.10). At high altitudes, the race time was significantly faster with caffeine than with placebo (P less than 0.001), both after one and two laps, 2.19% and 3.18% of the mean time, respectively (corresponding to approx. 101 s and 152 s). The perceived exertion was similar at low and high altitudes independent of medication. In conclusion, there are indications that caffeine induces an increased performance capacity for cross-country skiers at low altitudes. Furthermore, an even more marked improvement after caffeine as compared to placebo was found at high altitudes.

Adult↗

PubMed1991

Prevention of high-altitude pulmonary edema by nifedipine.

BACKGROUND: Exaggerated pulmonary-artery pressure due to hypoxic vasoconstriction is considered an important pathogenetic factor in high-altitude pulmonary edema. We previously found that nifedipine lowered pulmonary-artery pressure and improved exercise performance, gas exchange, and the radiographic manifestations of disease in patients with high-altitude pulmonary edema. We therefore hypothesized that the prophylactic administration of nifedipine would prevent its recurrence. METHODS: Twenty-one mountaineers (1 woman and 20 men) with a history of radiographically documented high-altitude pulmonary edema were randomly assigned to receive either 20 mg of a slow-release preparation of nifedipine (n = 10) or placebo (n = 11) every 8 hours while ascending rapidly (within 22 hours) from a low altitude to 4559 m and during the following three days at this altitude. Both the subjects and the investigators were blinded to the assigned treatment. The diagnosis of pulmonary edema was based on chest radiography. Pulmonary-artery pressure was measured by Doppler echocardiography and the difference between alveolar and arterial oxygen pressure was measured in simultaneously sampled arterial blood and end-expiratory air. RESULTS: Seven of the 11 subjects who received placebo but only 1 of the 10 subjects who received nifedipine had pulmonary edema at 4559 m (P = 0.01). As compared with the subjects who received placebo, those who received nifedipine had a significantly lower mean (+/- SD) systolic pulmonary-artery pressure (41 +/- 8 vs. 53 +/- 16 mm Hg, P = 0.01), alveolar-arterial pressure gradient (6.6 +/- 3.8 vs. 11.8 +/- 4.4 mm Hg, P less than 0.001), and symptom score of acute mountain sickness (2.0 +/- 0.7 vs. 3.9 +/- 1.9, P less than 0.01) at 4559 m. CONCLUSIONS: The prophylactic administration of nifedipine is effective in lowering pulmonary-artery pressure and preventing high-altitude pulmonary edema in susceptible subjects. These findings support the concept that high pulmonary-artery pressure has an important role in the development of high-altitude pulmonary edema.

Adult↗

PubMed2001

A comparison of the physiological response to simulated altitude exposure and r-HuEpo administration.

Concerns have been raised about the morality of using simulated altitude facilities in an attempt to improve athletic performance. One assumption that has been influential in this debate is the belief that altitude houses simply mimic the physiological effects of illegal recombinant human erythropoietin (r-HuEpo) doping. To test the validity of this assumption, the haematological and physiological responses of 23 well-trained athletes exposed to a simulated altitude of 2650-3000 m for 11-23 nights were contrasted with those of healthy volunteers receiving a low dose (150 IU x kg(-1) per week) of r-HuEpo for 25 days. Serial blood samples were analysed for serum erythropoietin and percent reticulocytes; maximal oxygen uptake (VO2max) was assessed before and after r-HuEpo administration or simulated altitude exposure. The group mean increase in serum erythropoietin (422% for r-HuEpo vs 59% for simulated altitude), percent reticulocytes (89% vs 30%) and VO2max (6.6% vs -2.0%) indicated that simulated altitude did not induce the changes obtained with r-HuEpo administration. Based on the disparity of these responses, we conclude that simulated altitude facilities should not be considered unethical based solely on the tenet that they provide an alternative means of obtaining the benefits sought by illegal r-HuEpo doping.

Adult↗

PubMed1988

Body and organ weights of rats exposed to carbon monoxide at high altitude.

Although chronic exposure to carbon monoxide (CO) or high altitude produces pronounced cardiovascular changes in humans as well as animals, there is little information on the effects elicited by these stressors combined. Theoretical considerations, as well as data from acute studies, suggest that CO inhaled at high altitude may be more detrimental than CO inhaled at low altitude. The purpose of these studies was to construct a system in which CO and altitude could be controlled precisely, and to investigate the effects of continuous exposure to CO and high altitude on body weights and hematocrit ratios, as well as heart, spleen, adrenals, kidneys, and pituitary weights. Male, laboratory rats were exposed for 6 wk in steel barometric chambers to (1) 100 ppm CO, (2) 15,000 ft simulated high altitude (SHA), and (3) CO at SHA. Altitude was simulated by a system of gate valves and a vacuum pump, and measured by an altimeter. CO, from high-pressure cylinders, was introduced into the air supplying each chamber through a mass flow controller and measured by a nondispersive infrared (NDIR) analyzer. Although SHA had no affect on left ventricle plus septum (LV + S), adrenal, spleen, or kidney weights, SHA decreased body weights, and increased hematocrit ratios, as well as right ventricle (RV), total heart (HT), and pituitary weights. CO had no affect on body weights, RV, HT, adrenal, spleen, or kidney weights, but CO increased hematocrit ratios and LV + S weights. There was no significant interaction between SHA and CO on any parameter except kidney weight. These results indicate that, in general, the effects produced by 15,000 ft SHA are not intensified by exposure to 100 ppm CO.

Altitude↗

PubMed2001

Muscle adaptation to altitude: tissue capillarity and capacity for aerobic metabolism.

Prolonged exposure to high altitude leads to reduced muscle mass and performance. The fall in muscle mass follows a reduction in fiber size, which at first was believed to be accompanied by increased fiber capillarization and aerobic enzymes. Subsequent studies showed that hypoxia alone does not alter capillary number and geometry in skeletal muscles of mammals at altitude. It was also found that alterations in fiber size and aerobic enzymes depend on a number of additional factors, including animal activity and the level of hypoxia (e.g., moderate vs. extreme altitude). With training at altitude, fiber capillary number and aerobic enzymes are increased, indicating that muscle potential for plasticity is conserved in hypoxia. Recent studies have also shown that capillary number and geometry are altered in muscles of several species of birds native or exposed to higher altitude; that is, that capillary growth can occur in skeletal muscle in response to chronic exposure to high altitude. In this mini review, we summarize these data and current knowledge on muscle capillary to fiber structural relationships and their implications for muscle aerobic function at altitude.

Adaptation, Physiological↗

PubMed2004

Transient high altitude neurological dysfunction: an origin in the temporoparietal cortex.

This case report describes three separate episodes of isolated ataxia, hallucinations of being accompanied by another person, and bilateral dressing apraxia occurring in a single individual without prior warning signs. These symptoms are attributable to disruption of vestibular processing in the temporoparietal cortex or associated limbic structures. Neurological dysfunction at high altitude is usually ascribed to high altitude cerebral edema or acute mountain sickness. However, transient neurological symptoms occur abruptly at more extreme altitudes, often following vigorous exertion, without overt altitude-induced prodromes. These symptoms may be caused by intense neuronal discharge or neuronal synchronization as a feature of epileptic discharges or cortical spreading depression. Transient high altitude neurological dysfunction should be recognized as a separate complication of extreme altitude, distinct from high altitude cerebral edema.

Acute Disease↗

PubMed2005

Acclimatization to oxidative stress at high altitude.

Hypoxia-mediated oxidative stress has been implicated in the pathophysiology of high altitude maladaptations. To explore whether prolonged exposure to high altitude can trigger an adaptive response to oxidative stress and restore redox homeostasis in the body, the study was conducted to evaluate biochemical variables related to oxidative stress and antioxidant status in humans at sea level (190 m) and following 3- and 13- month sojourns at altitude (4,500 m). After 3 months at altitude, whole-blood thiobarbituric acid reactive substances (TBARS) were significantly higher (65.6%), nonenzymatic antioxidants like ascorbic acid and caeruloplasmin were significantly lower (41% and 22%, respectively) and plasma total antioxidant status (TAS), glutathione levels, and superoxide dismutase activity were marginally altered as compared to their basal values. After 13 months at altitude, TBARS levels regressed back to preexposure levels. Plasma total antioxidant status (TAS) improved by 21%, glutathione levels by 32.8%, and plasma bilirubin by 35.8% as compared to sea level. Average concentrations of ascorbic acid and caeruloplasmin were 18% and 37% higher as compared to the subjects studied after a 3-month stay at high altitude. In addition, there was a progressive rise in erythrocytic superoxide dismutase activity and persistent hyperurecemia. The study observed that on prolonged exposure to high altitude humans could mount an effective adaptive response to oxidative stress by activating the antioxidant defense. Hence, strengthening the antioxidant defense could be an effective strategy to prevent free-radical-mediated pathophysiological alterations and quicken acclimatization to oxidative stress.

Acclimatization↗

PubMed2005

High altitude and the eye: a case controlled study in clinical ocular anthropometry of changes in the eye.

Tribal natives of two spatially separate districts of Lahaul-Spiti (mean altitude = 3300 m) and Kinnaur (mean altitude = 1,700 m) in the Himalayan state of Himachal Pradesh have lived for centuries as closed isolated groups, marrying within the local community up to the recent past. Studies on highland natives in the Andes have shown differences in chest diameters, lung volumes, hematocrit, and the like, in those living at high altitudes. We wanted to study whether stay at high altitude for generations confers any change in the ocular anthropometry. No study of this nature is available in the literature. We studied the ocular parameters using Snellen's charts, Standard Royal-Air-Force Rule, A-2,500 Sonomed A-Scan, Goldmann's aplanation tonometer, and S-7,000 Autorefractometer on 50 healthy volunteers at the Indira Gandhi Medical College Out Patient Department at Shimla (mean altitude = 2,100 m). Those living at higher altitudes in Lahaul-Spiti [LS] (n = 10) had significantly wider nose bridge width (p < 0.05); inter-inner canthal distance [IICD] (p < 0.05); inter-outer canthal distance [IOCD] (p < 0.05); and interpupillary distance [IPD] (p < 0.05) than the group living at Kinnaur (n = 40) at lower elevation. The LS group also had narrower palpebral fissure length in the vertical dimension (p = 0.05) and a lower IOP (p = 0.002) than the Kinnaur group. The axial length, lens thickness, and anterior chamber depth were comparable in the two groups. It appears that the eye and its adnexa respond to hypoxia, ultraviolet radiations, and persistent snow cover at high altitude by altering its anthropometry in a subtle but discernible manner. This was a hitherto unexplored area in the literature. Further studies to elucidate and substantiate the findings of the study are indicated.

Accommodation, Ocular↗

PubMed2006

Evidence for a genetic basis for altitude-related illness.

Altitude-related illnesses are a family of interrelated pulmonary, cerebral, hematological, and cardiovascular medical conditions associated with the diminished oxygen availability at moderate to high altitudes. The acute forms of these debilitating and potentially fatal conditions, which include acute mountain sickness (AMS), high altitude pulmonary edema (HAPE), and high altitude cerebral edema (HACE), often develop in incompletely acclimatized lowlanders shortly after ascent, whereas, the chronic conditions, such as chronic mountain sickness (CMS) and high altitude pulmonary hypertension (HAPH), usually afflict native or long-term highlanders and may reflect a loss of adaptation. Anecdotal reports of particularly susceptible people or families are frequently cited as evidence that certain individuals have an innate susceptibility (or resistance) to developing these conditions and, in recent decades, there have been a number of studies designed to characterize the physiology of individuals predisposed to these conditions, as well as to identify the specific genetic variants that contribute to this predisposition. This paper reviews the epidemiological evidence for a genetic component to the various forms of altitude-related illness, such as innate susceptibility, familial clustering, and patterns of population susceptibility, as well as the molecular evidence for specific genetic risk factors. While the evidence supports some role for genetic background in the etiology of altitude-related illness, limitations in individual studies and a general lack of corroborating research limit the conclusions that can be drawn about the extent of this contribution and the specific genes or pathways involved. The paper closes with suggestions for future work that could support and expand on previous studies, as well as provide new insights.

Acute Disease↗

PubMed1997

Glycophorin A somatic cell mutation frequencies in residents of Tibet at high altitudes.

Since cosmic radiation is absorbed by the atmosphere surrounding the Earth, people who live at high altitude receive significantly larger amounts of cosmic radiation exposure than do those who live at low altitude. The glycophorin A-based somatic mutation assay was performed on 36 blood samples from two populations of Tibet inhabitants to determine whether residents at high altitude (4,300 m) accumulate more somatic mutations than do those who live at low altitude (1,500-1,900 m). These two populations differ in estimated cumulative lifetime cosmic radiation dose, with high altitude residents having received a mean of 111 mSv while low altitude residents received a mean of 27 mSv. Results showed no significant difference in peripheral blood variant erythrocyte frequency between these two populations and no difference from results of a previous study on Finnish workers who live at very low altitude (<500 m).

Altitude↗

PubMed1995

Effects of exposure to high altitude on plasma endothelin-1 levels in normal subjects.

OBJECTIVE: To assess whether the hypoxia associated with exposure to high altitude affects plasma endothelin-1 levels, and whether changes in endothelin-1 are related to those in systemic and pulmonary blood pressure. DESIGN: Eight normal subjects ascended Mount Everest to an altitude of 5050 m within a period of 8 days (study 1) and 10 ascended Mount Rosa in the Italian Alps to an altitude of 4559 m within 2 days (study 2). In study 1 systemic blood pressure, heart rate, haematocrit, haemoglobin oxygen saturation (evaluated by percutaneous oximetry) and venous plasma endothelin-1 were measured several times during the ascent, and twice more during the time spent at high altitude. In study 2 the same parameters as well as systolic pulmonary pressure by echocardiography were evaluated on the second day of resting at 4559 m. In both studies, data obtained during the expeditions were compared with those collected from the same subjects at sea level. RESULTS: In study 1 plasma endothelin-1 increased progressively up to 4240 m (from 1.8 +/- 0.1 pg/ml at sea level to 2.7 +/- 0.2 pg/ml) and decreased slightly thereafter; these increments were directly related to the decrements in percutaneous oxygen saturation, which, at that altitude, fell from 98.6 +/- 0.2% at sea level to 80.8 +/- 0.4%. Blood pressure and haematocrit also rose in response to exposure to high altitude but these changes were not related to changes in endothelin-1. In study 2 the increments in plasma endothelin-1 were similar to those observed in study 1 and the changes again correlated with changes in oxygen saturation as well as with those in systolic pulmonary pressure. On average, systolic pulmonary pressure increased from 19 +/- 1 to 26 +/- 1.9 mmHg, whereas systemic blood pressure and haematocrit were unchanged. CONCLUSION: Exposure to high altitude is associated with consistent increases in plasma endothelin-1. This is probably the result of augmented secretion of the peptide in response to hypoxia and may contribute to the physiological adaptation of the pulmonary circulation to this condition.

Adult↗

PubMed2001

Role of airway receptors in altitude-induced dyspnea.

PURPOSE: The purpose of this study was to examine the role of airway receptors in respiratory-related sensations after ascent to altitude. METHODS: Ratings of respiratory-related sensations, perceived exertion and acute mountain sickness, heart rate, and peripheral oxygen saturation were recorded at rest and exercise in male and female subjects who had inhaled either aerosolized saline or saline with tetracaine after acute ascent to an altitude of 3500 m and after prolonged acclimatization of 18 d at altitudes between 4000 and 5000 m. RESULTS: Tetracaine had no effect on respiratory-related sensations at altitude either at rest or during exercise, and male and female subjects experienced similar respiratory-related sensations. Sensations of rapid breathing were experienced at rest after acute exposure to 3500 m as compared with sea level, but not after acclimatization to 5000 m. Sensations of rapid breathing, air hunger, and heavy breathing were experienced during exercise after acute and prolonged altitude exposure as compared with sea level, with a sensation of chest tightness experienced at 3500 m and a sensation of gasping experienced at 5000 m. CONCLUSION: These results suggest that airway afferents play no role in the respiratory-related sensations experienced by male and female subjects either during acute ascent to altitude or after prolonged acclimatization at altitude.

Adult↗

PubMed2004

Pregnancy at high altitude: a hyperviscosity state.

BACKGROUND: Pregnancy at high altitude has been associated with intrauterine growth restriction and preeclampsia. These conditions, at sea level, have been linked to increased hematocrit and blood viscosity. The aim of this study was to investigate the effect of high altitude on maternal hemorheology. METHODS: This was a cross-sectional study. We examined 94 pregnant women at 10-38 weeks of gestation resident at high altitude (4370 m above sea level) and 75 at sea level, and 24 and 17 nonpregnant women at each altitude, respectively. Blood and plasma viscosity, hematocrit, plasma fibrinogen, albumin and total protein concentrations were determined in blood samples obtained after an overnight period of fasting. RESULTS: Pregnancy at high altitude, compared to sea level, is characterized by higher hematocrit, blood viscosity (at high shear rate), plasma viscosity, total protein and fibrinogen concentrations (25%, 38%, 7%, 13.3% and 25%, respectively) and 6% lower albumin concentration. Nonpregnant women at high altitude, compared to sea level, had higher hematocrits, blood viscosity, plasma viscosity, total protein and fibrinogen concentrations (25%, 55%, 18%, 26% and 98%, respectively) and 13% lower albumin concentration. CONCLUSION: Pregnancy at high altitude compared to sea level is characterized by increased blood viscosity as a result of increased hematocrit and plasma viscosity.

Adult↗

PubMed2004

Maternal cardiac function during pregnancy at high altitude.

OBJECTIVE: To investigate the maternal cardiovascular adaptation in pregnancy at high altitude, compared with that at sea level. DESIGN: Cross sectional study. SETTING: Two maternity units providing routine antenatal care: one at 4370 m above sea level (Cerro de Pasco, Peru) and one at sea level (Lima, Peru). POPULATION: We examined 175 pregnant women at 5-41 weeks of gestation and 16 non-pregnant controls resident at high altitude and 132 pregnant women and 18 non-pregnant controls at sea level. METHODS: Two-dimensional and M-mode echocardiography of the left ventricle. MAIN OUTCOME MEASURES: Maternal cardiac output and left ventricular longitudinal and transverse systolic function indices. RESULTS: Pregnancy at high altitude, compared with sea level, is associated with 11% lower birthweight and 31% lower maternal cardiac output, due to 15% lower stroke volume and 11% lower heart rate. The lower stroke volume was due to a lower preload and impaired longitudinal and transverse left ventricular systolic function. Mean arterial pressure was about 8% lower during pregnancy at high altitude versus sea level. Pregnant women at high altitude failed to expand their intravascular space to the same extent as the sea level group: cardiac output increased by 17%, left atrial diameter by 12% and end-diastolic diameter by 1% at high altitude versus 41%, 25% and 5%, respectively, at sea level. CONCLUSIONS: Pregnancy at high altitude, compared with sea level, is characterised by lower cardiac output due to lower heart rate and lower stroke volume and reduced expansion of the maternal intravascular space compared with the non-pregnant state.

Adaptation, Physiological↗

PubMed2006

Maximal exercise and muscle oxygen extraction in acclimatizing lowlanders and high altitude natives.

The tight relation between arterial oxygen content and maximum oxygen uptake (Vv(o2max)within a given person at sea level is diminished with altitude acclimatization. An explanation often suggested for this mismatch is impairment of the muscle O(2) extraction capacity with chronic hypoxia, and is the focus of the present study. We have studied six lowlanders during maximal exercise at sea level (SL) and with acute (AH) exposure to 4,100 m altitude, and again after 2 (W2) and 8 weeks (W8) of altitude sojourn, where also eight high altitude native (Nat) Aymaras were studied. Fractional arterial muscle O(2) extraction at maximal exercise was 90.0+/-1.0% in the Danish lowlanders at sea level, and remained close to this value in all situations. In contrast to this, fractional arterial O(2) extraction was 83.2+/-2.8% in the high altitude natives, and did not change with the induction of normoxia. The capillary oxygen conductance of the lower extremity, a measure of oxygen diffusing capacity, was decreased in the Danish lowlanders after 8 weeks of acclimatization, but was still higher than the value obtained from the high altitude natives. The values were (in ml min(-1) mmHg(-1)) 55.2+/-3.7 (SL), 48.0+/-1.7 (W2), 37.8+/-0.4 (W8) and 27.7+/-1.5 (Nat). However, when correcting oxygen conductance for the observed reduction in maximal leg blood flow with acclimatization the effect diminished. When calculating a hypothetical leg V(o2max)at altitude using either the leg blood flow or the O(2) conductance values obtained at sea level, the former values were almost completely restored to sea level values. This would suggest that the major determinant V(o2max)for not to increase with acclimatization is the observed reduction in maximal leg blood flow and O(2) conductance.

Acclimatization↗