Thermal, metabolic, blood, and circulatory adjustments in prolonged outdoor exercise.

Thermal, metabolic, and circulatory responses were studied in six hill-walkers taking part in a 28-mile (45-km.) walk in rough country in autumn and winter, air temperatures being 6 to 12 degrees C. and -2 to 2 degrees C., respectively.Though they were an apparently well-matched party, the walkers had to split into three pairs to avoid exhaustion. They adjusted their clothing so that mean skin temperatures were similar in both warm and cold conditions, the average value being 30.5 degrees C. compared with the resting comfort range of 33 to 34.5 degrees C. When, on the winter trial, skin temperatures were lowered by reduction of clothing, mean skin temperatures fell to 26.5 to 27.8 degrees C., one subject showing a value of 21.3 degrees C. These temperatures were associated with moderate discomfort from cold.Gut temperatures during exercise, measured with a radio pill, averaged 38.7 to 37.9 degrees C. on the autumn exercise. Slightly lower values were observed in winter, but this was associated with slower walking rather than cold stress. A fat and a thin subject walking together with minimal clothing showed widely different temperature responses, the fatter subject having a lower skin temperature and higher gut temperature than his companion. These results were compared with other results on extreme cold stress and discussed in relation to hypothermia. Heart rate and blood pressure findings were unremarkable, except for increased post-exercise heart rates and standing/lying heart rate differences, and a tendency to postural hypotension associated with exhaustion. Blood volume was not reduced in exhaustion and there were no significant changes in blood electrolytes or other constituents apart from a small rise in potassium. Ketonuria developed in all subjects.