Mountaineering sojourn: effects on body composition of prolonged exposure to high altitude in a cold environment

Partitioned weight loss and body composition changes during a mountaineering expedition: a field study

Weight loss and changes in body composition are recognized phenomena associated with high-altitude mountaineering expeditions. Attempts to partition the weight loss between fat mass (FM) and fat-free mass (FFM) have been inconclusive. Therefore, five male subjects, average age 40.0 +/- 5.5 years, were studied prior to, during, and following a 21-day expedition between 2200 m and 4300 m on Mt. McKinley, Alaska. Pre- to postexpedition body composition changes were determined by densitometry, skinfold thickness (12 sites), body girth measurements (14 sites), and cross-sectional area from magnetic resonance imaging (MRI) (three sites). Data analysis by Student's t-test (p < 0.05(1) tail) indicated decreases in body weight (4.2 +/- 2.8 kg, 220 g/day, 5.4% of initial weight), total skinfold thickness (10.8%), total body girth (2.8%), and percentage of fat by densitometry (15%). Total cross-sectional area of the three MRI slices (upper arm + thigh + calf) decreased 4.7%, muscle area decreased 9.1%, and fat area decreased 3.9%. The three methods used to partition the weight loss between FM and FFM did not agree: 77% FM vs 23% FFM by densitometry, 25% FM vs 75% FFM by skinfolds, and 38% FM vs 62% FFM by MRI. Energy intake (3640 +/- 1250 kcal/day) was negatively correlated (Pearson r > 0.88(2) tail) with losses in weight (r = -0.89), skinfolds (r = -0.93), and girths (r = -0.88), ie the greater the intake the less the decline. Therefore, insufficient energy intake appeared primarily responsible for the weight loss and changes in body composition during the expedition.

Physiological changes induced by pre-adaptation to high altitude

To study the physiological effects of pre-adaptation to high altitude, seven subjects were submitted to acclimatization at 4350 m followed by intermittent acclimation in a low barometric pressure chamber (5000 m to 8500 m). The subjects then spent 25 days in the Himalayas. Ventilatory and cardiac responses were studied during a hypobaric poikilocapnic hypoxic test performed both at rest and during exercise (100 W) in normoxia and in hypoxia (barometric pressure: 589 hPa, altitude: 4500 m). Haemoglobin, erythrocytes, reticulocytes, packed cell volume, 2,3-diphosphoglycerate (2,3-DPG) and erythropoietin (EPO) were measured. All variables were studied before pre-adaptation to high altitude (A), after the acclimatization period (B), after the acclimation period (C) and after the expedition (D). The ventilatory and cardiac responses were characterized by an increased tidal volume in hypoxia (+33% during exercise in B, P < 0.05; +100% at rest and +33% during exercise in C, P < 0.05) without any change in respiratory frequency, whereas an increased systolic blood pressure was only observed in C during exercise in hypoxia [+23 mmHg (3.07 kPa), P < 0.01]. Arterial O2 saturation was higher in hypoxia in C and D, both at rest (+8.2% and +4.7%, P < 0.01, respectively), and during exercise (+6.3% and +6.3%, P < 0.01, respectively). Erythrocytes, haemoglobin and packed cell volume did not vary significantly. The number of reticulocytes was higher in B (+172%, P < 0.05) and in C (+249%, P < 0.05). EPO and 2,3-DPG increased only in C (+770%, P < 0.01 and +23%, P < 0.05, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)