PARIS — A third of the world's adults are physically inactive, and the couch potato lifestyle kills about five million people every year, experts said in the medical journal The Lancet on Wednesday. "Roughly three of every 10 individuals aged 15 years or older -- about 1.5 billion people -- do not reach present physical activity recommendations," they said in a report that described the problem as a "pandemic." The picture for adolescents is even more worrying, with four out of five 13- to