Essay: DON'T JUST SIT THERE; WALK, JOG, RUN

CONSIDER the human machine in middle age: atrociously maintained, rusty from disuse. None of its parts—the bellows, the tubes, the pump—function as efficiently as they once did. The muscles have degenerated into blancmange. If, in an emergency, the demand for air rises abruptly from the idling requirement of six to eight quarts a minute to 100 quarts or more, the maw gulps like that of a beached carp. The heart throbs about two to three times its customary rate, pumping blood through pipes thickened by sedimentary deposits and grown inelastic with age....

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