He promoted exercise. In an era when life expectancy was 35 to 40 years, Franklin lived to 84, thanks to an exercise regimen emphasizing intensity. He realized a workout needed to produce cleansing sweat that carries away toxins and recognized the importance of raising the heart rate. Walking a mile up and down stairs produced five times more body heat than walking a mile on the level, he noted. He calculated that when swinging weights that resembled today’s popular kettle bells his pulse rate went from 60 to 100 beats per minute. (The Granger Collection, New York)