Endurance of preheated men in exhausting work.

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Abstract
Four men walked to ex-haustion up a grade beginning at 10% and increasing by 1% at the end of each minute. In training at 18[degree]C, the average endurance was 712 sec. In 18 tests at 46[degree]C, the men were heated in a tub of water on different days to approximately 37.2, 37.8, 38.3, 38.9, and 39.2 C before the walks. As the time in the bath increased from day to day, the heart rate and rectal temperature before the walk increased and walking time decreased. The shortest walk lasted 93 sec; the heart rate in the standing position before this walk was 177 beats/min. In standing, the heart rate increased with mean body temperature (r = 0.88). The walks shortened as the standing heart rate increased (r = -0.90). During the walks the heart rate increased without leveling off to a final average of 201 beats/min; this did not vary significantly with walking time. The walking time was proportional to the difference between the final and standing heart rates (r = 0.88). The reduction in endurance associated with preheating was attributed to the narrowing of the margin available to the heart for an increase in rate.

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