at least 20 percent is several times the minimum recommended by the World Health Organization, researchers said Wednesday.The same applies to breast and bowel cancer, they reported in a study reviewing 35 years of research on the link between physical exertion -- whether gardening or long-distance running -- and five chronic diseases. The benefits of exercise are well known and beyond dispute.Most health authorities issue guidelines on the bare minimum required to help ward off numerous ailments made worse by a sedentary lifestyle.
But despite a mountain of research, "we still do not definitively know how much the type and quantity of physical activity reduces the risk of common conditions," a team of scientists led by Hmwe Kyu of the Institue for Health Metrics at the University of Washington in Seattle said in a statement.
One problem has been finding a unit of measure that can be applied to actions as varied as walking one's dog, jumping rope, or having sex.Enter the MET, or "metabolic equivalent of tasks", a concept developed in the 1990s and adopted more recently by the WHO.Metabolism is the conversion of food and drink into energy. When we are at rest -- watching television, for example -- we have a metabolic rate of "one". Using this as a baseline, scientists assign values to different activities depending on how much energy they consume.