Abstract
Summary
The tolerance of altitude-acclimatized (18,000 ft 4 wk) and unacclimatized rats to exercise at 5° was determined. Fewer unacclimatized than acclimatized rats became fatigued during 9 hr of exercise in the cold. Normal body temperatures were maintained in both groups during 9 hr in the cold at rest, but after exercise unacclimatized rats became mildly hypothermic (body temperature 35°) and acclimatized rats severely hypothermic (body temperature 27.9°). Poly-cythemia (hematocrit 69) was produced during the altitude acclimatization. Altitude-acclimatized rats developed more severe hypoglycemia and lower liver glycogen and serum lactic acid concentrations after exercise than did controls. No pathological changes were found in resting altitude-acclimatized rats, but after exercise in the cold, a higher percentage of acclimatized than unacclimatized rats developed focal myocardial necrosis within 4 days. Reduced exercise tolerance is attributed to severe hypothermia with associated decreased metabolism, polycythemia, hypoglycemia, and a higher incidence of pathological changes in the cardiac and striated muscles.
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