The Study of Exercise: One way to prevent colds, he argued, was regular exercise. The best way to measure exercise, he argued, was not by its duration but “by the degree of warmth it produces in the body.” This was one of the first theories linking exercise to calories of heat. For example, he explained, walking a mile up and down stairs produced five times more body warmth than walking a mile on a level surface. When swinging weights, Franklin calculated that this raised his pulse from 60 to 100 beats per minute. Again, he rightly calculated that body “warmth generally increases with
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