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Original Article
Volume 47 - No.1:January 2003 (index)

Indian J Physiol Pharmacol  2003;

Oxygen Saturation Response to Exercise VO2 at 2100 m and 4350 m in Women Mountaineering Trainees

Defence Institute of Physiology and Allied Sciences,
Lucknow Road, Timarpur,Delhi- 110 054
(Received on July 22, 2001

Abstract : Human work performances decreases at high altitude (HA).  This decrement does not appear to be similar for every individual, may be due to variety of factors like elevation, mode of induction, work intensity, physical condition and specificity of the subjects.  The purpose of the study was to evaluate the effects of alteration in responses of oxygen saturation (SaO2) and oxygen consumption (VO2) to a standard exercise in women mountaineering trainees under hypobaric hypoxia.  Experiments were conducted in 2 groups (10 each) of females and compared the difference in responses of native women of moderate altitude with those of the plains/low altitude.  A standard exercise test (Modified Harvard Step-Test for women) was performed on a 30 cm stool with 24 cycles/min for 5 min, initially at 2100 m and then at 4350 mThe exercise VO2 values for plains dwelling women achieved apparently VO2max level at both altitude locations with significant reduction in SaO2 during standard exercise.  Exercise VO2 values decreased on exposure to 4350 m, with further reduction in SaO2 . Whereas with same work intensity, under same situation the exercise VO2 values of the moderate altitude women did not appear to have reached VO2max. They also maintained comparatively higher level of SaO2. It may be concluded that hypoxic exposure along with mountaineering training, the moderate altitude women maintained a higher level of SaO2 during standard exercise at both altitude locations, compared to low altitude women who might have lost a compensatory reserve to defend the hypoxic stress to exercise.  Thus, moderate altitude women are proved to be better fit for hypoxic tolerance/HA performance.

 Key words : high altitude, women,VO2max, oxygen, saturation, modified harvard, step-test



High altitude (HA) poses several operational problems to the sojourners, soldiers as well as mountaineers.  During, ascent to HA, a progressive decrease in atmospheric oxygen pressure severely affect the oxygen gradient between atmospheric air and muscle.  Maximum aerobic capacity is used as a performance index and generally accepted as the best single measure of the functional limit of the combined cardiovascular and respiratory system to delivery adequate amount of oxygen to the active muscles and demonstrate the capability of the muscle to use oxygen.  The decrement of maximal work capacity (VO2max) of sojourners under HA hypoxic condition is well documented at various altitudes during both acute and prolonged exposure (1-5).  The decrement of oxygen consumption is directly related to the decrease in partial pressure of oxygen at HA (6, 7), even though the rate and magnitude of decrease varies with the elevation, mode of induction, status of hypoxic adaptation, exposure duration, level of activity and sojourner's place (altitude) of birth/residency, etc. (8, 9).  Endurance trained athletes with larger aerobic capacities (>60 ml/kg/min) appear to be selectively affected, demonstrating larger declines in VO2max at altitude (3,000-4,300 m) compared with the untrained individuals with lower aerobic capacities (10-12).  The completeness of pulmonary gas exchange system may play a vital role in the individual variation of this apparent training status/altitude/ VO2max relationship (5, 12, 13).  The decrease in arterial oxygen saturation (SaO2) during maximal exercise at sea level as well as mild and moderate altitudes have been reported (2).  It has been demonstrated that both SaO2 and the ratio of lung diffusion capacity to VO2max during maximal exercise is highly correlated to the decline in VO2max from sea level to altitude (10, 12).  Oxygen hemoglobin dissociation curve is sigmoid in nature, which allows arterial PaO2 to be reduced during exercise to as low as 75-80 mm Hg with only a small percentage reduction in SaO2 Once PaO2 falls below approximately 75 mmHg, a relative small change in PaO2 begins to have much larger effect on SaO2. Chapman et al (14) examined the relationship between the degree of arterial oxygen desaturation during maximal exercise at sea level in highly trained athletes and the decline in SaO2 and VO2max at a mild (simulated) altitude.  However, no field study appears to have been carried out to evaluate the effects of mountaineering training on the changes in exercise oxygen consumption as well as the changes in SaO2 to a standard exercise under hypoxic conditions on women residents of moderate altitude and plains.  The mountaineering training course conducted by Himalayan Mountaineering Institute (HMI), Darjeeling, India provided an unique opportunity of carrying out this field study on women during mountaineering training in the Eastern Himalayas.  The purpose of the present study was to determine the response changes in end exercise VO2 and SaO2 during standard exercise at 2100 m and 4350 m on 2 groups of women, due to mountaineering training with altitude adaptation, inducted gradually by trekking to 4350 m with a view to evaluate the performance relationship between the native women of moderate altitude and the plains dwelling females.


Experiments were conducted on 20 women trainees, who had come to Himalayan Mountaineering Institute (HMI), Darjeeling (2100m) for a basic mountaineering course.  The subjects were selected randomly from a total strength of 63 trainees.  They all were Indians and belonged to middle class socioeconomic status. Out of these, 10 were residents of moderate altitude (2000-2100 m) and the remaining 10 belonged to the different plain regions (altitude not more than 260m) of India.  Maximum care was taken to match both the groups in respect of age, height and body weight.  After a practice run of the tests the volunteers gave informed consent.  They were also aware of their rights to withdraw from the experiments at any time.  The protocol was approved by the Ethic Committee of the Institute.  All the subjects were medically examined to rule out any systemic illness.  The personal history indicated about their good health, active physique and high motivation.  The ambient temperature at Darjeeling during

The course of study ranged between 7-21 ºC. The study was conducted in to phases : (i) Initial pre-training recordings were carried out at HMI (2100 m), in the temperature maintained (16-20 ºC) MI room at the commencement of the course.  All the pre-climbed tests were completed within three days of arrival of the subjects at HMI. (ii) On induction to 4350 m by trekking the standard exercise test was repeated after three days of sojourn at the base camp of HMI (4350 m), inside the silver hut, where the temperature was maintained between 17-20 ºC.  All the tests were conducted by the same group of observers with same set of equipment in both the situations.  Prior to the tests, the subjects rested in the temperature maintained room for 30 – 35 min.

Pulmonary ventilation (VE ) and respiratory frequency (Rf) were recorded with the help of ventilation monitor (P.K. Morgan, England) using a low resistance breathing valve fitted with mouth piece and nose clip.  Expired air was analyzed for O2 and CO2 content by rapid response Zirconium O2 analyzer and 901-MK2 CO2 analyzer (P.K. Morgan, England).  Heart rate was recorded by telemetric method using sports tester (Model PE = 3000, Finland).  Arterial oxygen saturation (SaO2) was measured with the help of a finger-oximeter (Nellcor, USA) calibrated before and after each study.  The standard exercise test was performed by using a portable wooden stool of 30 cm high with 24 cycles/min for 5 min (modified Harvard Step-Test for women).  The same stool was used in both phases to ensure uniformity in the step-test.  In the absence of any transport it was not possible to carry the heavy bicycle ergometer to 4350 m by porter/yak. Under the circumstances in the field situation, the observers had no choice but to perform the standard exercise test on the wooden stool (modified Harvard Step-Test for women). Harvard Step-Test is a standard method of exercise for assessing physical performance, particularly under field conditions.  Sengupta et al (15) compared Harvard StepTest "scores" of 20 soldiers with their 1 mile running time in the field and had found this is a fairly good method for measuring physical efficiency, which was comparable with field performance.  The O2 and CO2 analyzer modules of exercise test assembly (P.K. Morgan, England) were taken to HA separately.  Monitoring of Rf, VE ,V02, HR and SaO2 was done initially and thereafter every min during exercise.  VE was corrected to BTPS and the VO2 and VCO2 were corrected to STPD.  The criteria for the assessment of VO2max includes (a) a heart rate in excess of 90% of age predicted maximum (220 - age), (b) a respiratory exchange ratio of >1.10 and (c) a plateau (<150 ml increase) in VO2 with the increase in work.  If at least two of the three criteria were met, the highest VO2 recorded was chosen as the subject's VO2max.

At Darjeeling, the subjects had to undergo a rigorous training schedule of mountaineering activities for a period of one week from early morning till late evening with intermittent breaks.  After a week's training, they set their journey to the base camp (4350 m).  The trainees were transported (160 km) by bus (day-1) from Darjeeling to Yoksom (2200m).  Next morning (day-2) all the trainees trekked for about 15 km and reached Bhakim (2750 m( in 5-7 h where they stayed for the next day (day-3)).  On day-4, the subjects ascent on foot to Zamlingaon (3660 m) after crossing over a height of 4500 m, covering a distance of 12 km in 5 - 7 h and halted there for the next day (day-5) for acclimatization.  On day 6 the trainees about 14 km in 5-7 h and reached base camp of HMI at Chaurikhang (4350 m), located at the base of the peak Kanchanjangha, in the Eastern Himalayas.  The trekkers were trekking at about 23 km/h for 5-6 h each day, while carrying about 15 kg, load on their body.  During stay at intermittent altitudes of 2750 m and 3660 m as well as at 4350 m the subjects were hiked to higher elevation and brought back to the camp.  They were also engaged in different mountaineering activities for 4 - 5 h each day, which was an integral part of the training schedule for acclimatization.  Thus, the subjects experienced greatest physical strain while trekking to base camp as well as during sojourn.

On day 7-16 all the subjects stayed at 4350 m in the hut made of metal sheets fitted with bunks and used winter clothing.  There they had undergone intense mountaining activities like glacier -marching, ice cutting, peak assault, back packing, repelling, rock climbing etc. and were engaged in snow bound field areas at higher elevations in the forenoon and nearby camp areas in the afternoon.  The maximum and minimum ambient temperatures at the base camp during the period of study were +10 ºC and –7 ºC, respectively.  The clear sunshine and partial cloudiness during the day with occasional snowfall and high velocity wind are the characteristic features of environment there.

Two way classification of analysis of variance technique using Newman Keuls multiple range test has been used for the statistical analysis of the data, to compare the same group at different situations.  Unpaired t-test for the comparison of two different groups for each situation has been used.  Mean ± SD values are presented in the text/tables and P<0.05 has been used as level of significance.


Physical characteristics of both the groups are quite similar.  The mean ± S.D value of age and height for moderate altitude women were 20.2 ± 2.6 yrs and 150.5 ± 5.6 cm and for the low altitude women were 21.1 ± 3.4 yrs and 156.5 ± 4.1 cm, respectively.  The body weight showed very negligible fluctuations.  The values being 46.4 ± 6.4 and 46.7 ± 6.3 kg for moderate altitude women and 47.5 ± 5.6 and 47.4 ± 5.4 kg for low altitude women respectively, at 2100 m and 4350 m. The initial resting SaO2values (98%) were similar for both the groups at 2100 m altitude.  On gradual ascent to 4350 m both the groups showed significant reduction (P<0.001) in SaO2. The values being 89% and 87.1% respectively, for moderate altitude and plains dwelling women.  The magnitude of all (2%) was comparatively (P<0.05) more for the plains dweller at HA. Data of standard exercise tests for both the groups at 2100 m and 4350 m are presented in Table I. It appears from the responses of different variables that women from the plains have achieved end exercise VO2 value almost to the level of VO at both the altitude locations, as has been judged by the fact that, subjects of this group met two of the three criteria for assessment of VO2max. The subjects of this group were exhausted completely by the end of 5 min exercise.  Whereas the moderate altitude women did not appear to have achieved VO2max under the same circumstances.  The subjective opinion of the volunteers of' this group (moderate altitude women) were that they would have continued the step test exercise for furthermore time to reach maximum VO2 (VO2max). It appears, they required higher stimulus for attainment of exercise oxygen consumption to VO2max level.  During exercise at 4350 m low altitude women showed a significant reduction in exercise VO2 values compared to that of their own record at 2100 m (42.47 ± 4.12 ml/kg/min Vs 40.04 ± 4.26 ml/kg/min; P<0.05), whereas the native women of moderate altitude did not demonstrate any marked reduction in oxygen consumption (37.44 ± 5.11 ml/kg/min Vs. 36.79 ± 4.66 ml/kg/min) at the end of exercise at 4350 m. The SaO2 values of low altitude women reached 86.80 ± 1.65 % during standard exercise at 2100 m, as against their resting value of 98% (D 11.2%).


Table I

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Table I: Mean ± S.D. values of various physiological parameters of both the groups during standard exercise at 2100 and 4150 m.

This reduction in end exercise SaO2 value is significantly (P<0.05) more compared to that of the values of moderate altitude women (90.60 ± 0.97 %; D 7.4%). During standard exercise at 4350 m, SaO2 values decreased further to 71.20 % and 77.3 % respectively for the women of plains and moderate altitude.  This indicates a fall of 26.8 % and 20.7 % respectively, compared to the initial resting value of' 98 % at 2100 m.  When compared with the resting SaO2 values at 4350 m, the reduction in SaO2 during exercise were 15.9 % and 11.7 % respectively, for low and moderate altitude womenThus the magnitude of fall in SaO2 during exercise was markedly pronounced in plains dwelling women compared to their counterparts of moderate altitude.  Pulmonary ventilation, respiratory frequency and ventilatory equivalent for oxygen increased significantly at 4350 in, while the exercise HR showed a reduction in both the groups.  The resting HR of both the groups recorded initially at 2100 m showed significantly (P<0.01) elevated value in low altitude women. On induction to 4350 m HR rose similarly for both the groups which were moderate but significant (P<0.01).


The unique feature of the present study was that, the women trainees reached 4350 m gradually by trekking under progessive hypoxia at increasing altitude following staging acclimatization, associated with rigorous mountaineering activities. Immediately on reaching at 4350 m, they were undergoing regular mountaineering activities, without showing, any clinical manifestations of severe fatigue or strain.  None of these women exhibited any symptoms of discomfort or acute altitude sickness.  They all ate well, slept well, worked well with maintenance of body weight.  The maintenance of body weight at HA is an interesting observation which has been described elsewhere.


The decrease in SaO2 on exposure to HA in all the subjects is due to hypoxia.  At HA the reduced oxygen supply to the blood decreases SaO2 even after an increase of HR. The rise in HR increases cardiac output to compensate for the decrease in blood oxygenation (16, 17), though the magnitude of fall in SaO2 was comparatively less in moderate altitude women.  This advantage may be primarily due to their place (altitude) of birth/residency.  The factors responsible for this difference between the groups may be due to different climate, physical environment, normal daily routine, social culture, pattern of living as well as status of acclimatization.  The result of the present study indicate that the oxygen consumption of the plains dwelling females born and raised at altitude not more than 260 m) to a standard exercise at 2100 m, has apparently reached the level of  VO2max, with marked reduction in SaO2 (D 11.2%). As expected with same schedule of exercise, at 4350 m, the exercise VO2 decreased with further reduction in SaO2values. On the contrary, with same level of work intensity at same situation (2100 m) the oxygen consumption of the native women of moderate altitude (born and raised at 2000 – 2100 m) did not appear to have achieved VO2max with maintenance of higher level of exercise SaO2. On induction to 4350 m by trekking resulting gradual acclimatization, no marked change was observed in exercise VO2 compared to their initial performance at 2100 m.  The magnitude of fall in SaO2 during standard exercise at 4350 m was also less compared to that of the values of low altitude women.  The observation of the better maintenance of SaO2 during standard exercise at both the study locations by the native women of' moderate altitude compared to their counterparts, suggests that the low altitude women are not able to overcome the higher degree of pulmonary gas exchange limitations during exercise at both altitude locations, which might have lost a compensatory reserve to defend the hypoxic stress to exercise.  Our results further indicate that the magnitude of decline in arterial oxygen saturation during standard exercise at 2100 m influence the ability to defend exercise VO2 at higher altitude (4350 m).  Thus it can also be suggested that low altitude women who display greater decline of end exercise SaO2 during standard exercise at lower hypoxic condition (2100 m) are more prone to decline in exercise O2 consumption at higher hypoxic situation (4350 m), compared with moderate altitude women.  Evident conclusion can be made from these findings that the moderate altitude women are better fit compared to low altitude women with respect to hypoxic tolerance/HA performance.

Elliot and Atterbom (17) and Patterson et al (18) observed that women tend to adapt to endurance training at altitude in a manner similar to men and also capable of performing hard work at high altitude.  Gore et al (5) and Terrados et al (2) observed that the reduced exercise SaO2 and pulmonary gas exchange limitations must impose a greater susceptibility to VO2max decline at mild altitude.  Chapman et al. (14) proposed that elite endurance athletes display varying degrees of pulmonary gas exchange limitations during maximal normoxic exercise and many demonstrate reduced arterial oxygen saturation (SaO2) at VO2max. They concluded that athletes who display reduced measures of SaO2 during maximal exercise in normoxia are more susceptible to declines in VO2max in mild hypoxia compared with the normoxic athletes.  Their observations support our findings. 

During maximal exercise vigorous hyperventilation occurs which may results in maintaining SaO2 and VO2max (19, 20).  Increase in pulmonary ventilation during exercise at high altitude can theoretically improve SaO2 by raising the alveolar PO2 and by left shifting in the oxygen hemoglobin dissociation curve.  In our studies, both the groups showed significant increase in ventilation as well as ventilatory equivalent for oxygen (VE/VO2 ) to a standard exercise at 4350 m indicates alterations in exercise ventilation in two different hypoxic situations might affect the changing exercise VO2 . 'This appears to be dependent upon ventilatory influences on SaO2 maintenance to some extent.  Pulmonary gas exchange limitations to exercise may also display in important role (21).  Powers et al. (22) suggested that pulmonary gas exchange limitations caused a significant reduction of VO2max of approximately 1% for every 1% reduction in SaO2 below 92%.  While Chapman et al. (14) suggested approximately a 0.5 % reduction in VO2max for every 1% drop in SaO2 below 92 %.  During exercise at high altitude the study groups showed varying degree of change in SaO2 between two hypoxic conditions.  The low altitude women showed (D 26.8%) fall of SaO2 and a significant reduction in exercise VO2. It appears that the low altitude women were not able to prevent exercise VO2 decrement at high altitude even by significant increase in metabolic and ventilatory demands.  Whereas the moderate altitude women did not achieve maximum oxygen uptake and maintained the almost same exercise oxygen consumption as that of the initial value at 2100 m with less fall in SaO2  (20.7%), even though both the study groups undergone same protocol of mountaineering training and same intensity of standard exercise test.  Gore et al. (5) demonstrated a significant reduction in VO2max (5.3 ml/kg/min or 6.9%) in 11 elite level cyclists at a very mild simulated altitude of 580 m.  Again, the VO2max of a physically active but untrained group did not change with mild hypoxia.  It has been suggested that pulmonary gas exchange limitations and reduced exercise SaO2 present in many endurance trained athletes must impose a grater susceptibility to VO2 reduction at mild altitudes.  In this study both the groups undergone same training schedule throughout the mountaineering course, thus it may not be due to the training during the course alone.  It can be suggested that, the maintenance of oxygen consumption to a standard exercise at higher altitude might be due to better ability to withstand more strain which may be dependent on some other factors.  The moderate altitude women are forced to undergo physical exertion while carrying out their normal daily activities due to rugged and steep hilly terrain.  Besides, being exposed (born and raised) to different climate and physical environment these women differ in their social culture and pattern of living.  From very young age, they are habitually climbing with or without load and this being one of their major daily routines, whether it is for education and/or occupation.  The level of habitual physical activity of these women associated with the daily schedule of work along with intense mountaineering training might have exerted in considerable influence on the level of aerobic capacity and thus improved the capability to defend the hypoxic stress at high altitude.  Compared with the study of Chapman et al. (14), our approach for better maintenance of SaO2 during a standard exercise at both the altitude situations suggests a smaller effect on pulmonary gas exchange limitations on oxygen consumption in moderate altitude women and thus proved to be better fit for hypoxic tolerance/HA performance. 


The authors are grateful to Col.  H. S. Chauhan, VSM.  Principal, Major R. Verma, Medical Officer and staff of HMI, Darjeeling for providing all the facilities for field trials.  Warm thanks are due to all the women trainees who volunteered as-subjects.


1.       Balke B, Nagle FE, Daniels J. Altitude and maximal performance in work and sports activity. JAMA 1965; 194:646-649.

2.       Terrados N, Mizuno M, Anderson. Reduction in maximal oxygen uptake at low altitudes: Role of training status and lung function. Clin Physiol Oxf 1985; 5:75-79.

3.       Grover RE, Weill JV, Ruves JT. Cardiovascular adaptation to exercise at high altitude. In: Exercise and Sports Sciences Reviews. New York: MacMillan 1986; pp-269-300.

4.       Cymerman A, Reeves JT, Sutton JR et al. Operation Everest II. Maximal oxygen uptake at extreme altitude. J Appl Physiol 1989; 66: 2446-2453.

5.       Gore CJ, Hahn AG, Scroop GS et al. Increased arterial desaturation in trained cyclists during maximal exercise at 580 m altitude. J Appl Physiol 1996; 80:2204-2210.

6.       Fragraeus L, Karlson J, Linnarsson D, Saltin B. Oxygen uptake during maximal work at lowered and raised ambient air pressures. Acta Physiol Scand 1973; 87: 411-421.

7.       Boutellier, Marconi C, Di Prampero PE, Cerretelli P.  Effects of chronic  hypoxia  on  maximal performance. Bull Europ Physio-Path Resp 1982; 18: 39-44.

8.       Shephard RJ, Boutlet E, Vandewalle H, Monod H. Peak oxygen uptake and hypoxia. Int J Sports Med 1988; 9: 483-488.

9.       Purkayastha SS, Ray US, Arora BS, Chhabra PC, Thakur L, Bandopadhyay P, Selvamurthy W. Acclimatization at high altitude in gradual and acute induction. J Appl Physiol 1995; 79: 487- 492.

10.    Lawler J, Powers SK, Thompson D. Linear relationship between maximal oxygen uptake and VO2max decrement during exposure to acute hypoxia. J Appl Physiol 1988; 64: 1486-1492.

11.    Young AJ, Cymerman A, Burse RL. The influence of cardiorespiratory fitness on the decrement in maximal aerobic power at high altitude. Ear J Appl Physiol 1985; 54: 12-15.

12.    Gavin TP, Stager JM, Derchak PA. Ventilation's role in the decline in VO2max and SaO2 in acute hypoxic exercise. Med Sci Sports Exerc 1998; 31: 195-199.

13.    Blomqvist G, Johnson RL Jr., Saltin B. Pulmonary diffusing capacity limiting human performance at altitude. Acta Physiol Scand 1969; 76: 284-287.

14.    Chapman RF, Emery M, Stager JM. Degree of arterial desaturation in normoxia influences VO2max decline in mild hypoxia. Med Sci Sports Exerc 1999; 31:658-663.

15.    Sengupta J, Verma SS, Joseph NT. A simple test for assessment of physical fitness. Sports Med 1973; 2:80-92.

16.    Hannon JP, Voggel JA. Oxygen transport during early altitude acclimatization: A perspective study. Ear J Appl Physiol 1977; 36: 285-297.

17.    Elliot PR, Atterborn HA. Comparison of exercise responses of males and females during acute exposure to hypobaria. Aviat Space Environ Med 1978; 49:415-418.

18.    Paterson DJ, Pinnington H, Pearce AR, Morton AR. Maximal exercise cardio-respiratory responses of men and women during acute exposure to hypoxia. Aviat Space Environ Med 1987; 58: 243-247.

19.    Dempsey JA, Hanson PE, Henderson KS. Exercise induced arterial hypoxemia in healthy persons at sea level. J Physiol (Lond) 1984; 355; 161-175.

20.    Sutton JR, Reeves JT, Wagner PD et al. Tolerable limits of hypoxia for the lungs: Oxygen Transport. In: Hypoxia: The tolerable limits. Indianapolis: Benchmark 1988; pp.l23-130.

21.    Dempsey JA, Exercise induced imperfection in pulmonary gas exchange. Can J Sport Sci 1987; 12:66s-70s.

22.    Powers SK, Lawler J, Dempsey JA, Dodd S, Landry G. Effects of incomplete pulmonary gas exchange on VO2max. J Appl Physiol 1989; 66: 2491-2495.


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