Fitness Tracker: Humans, once in constant motion as hunters and gatherers, are moving less than ever. At first, this trend seemed like progress: Transferring our heavy and dangerous work to animals, then machines, enabled more people to live longer. As recently as the 1950s, doctors considered exercise dangerous for people over age 40; for heart disease, which was then killing a record number of Americans, they prescribed bed rest. This was partly based on their concept of what “exercise” was: Early physiologists conducted studies on their (typically young, male) graduate students or on military servicemen — and in order to become more fit than they already were, these subjects needed to work out hard. “The mantra was, you have to go to a gym, you have to do high-intensity physical activity,” says Abby C King, a professor of health research and policy and medicine at Stanford University: “this sort of ‘no pain, no gain’ phenomenon.”
That notion began to change with the 1968 publication of “Aerobics,” by Kenneth Cooper, an Air Force physician, who argued that anyone could take measures to prevent heart disease with regular “aerobic” exercise, like swimming or jogging, that increases heart rate and oxygen uptake, “improving the overall condition of the body” and thereby “building a bulwark against many forms of illness and disease.” But it was hard to tease apart whether physical activity made people healthier or whether healthier people were more likely to be active. In a landmark study published in 1989, Cooper and colleagues tried to address this problem by considering subjects’ physical fitness, a metric determined by assessing performance on a treadmill test. Theirs is believed to be the first long-term study of men and women to show that the higher a person’s fitness level, the lower their risk of mortality, especially from cardiovascular disease and cancer. But physical fitness, they noted, is not the same as physical activity, the amount of movement a person gets in the course of their daily life. The only way researchers could learn about the latter was by asking people to describe their behaviour — a much less precise method than measuring their cardiovascular capacity in a lab.
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