New Delhi, Oct. 12 -- "WALKING IS MAN'S best medicine," said Hippocrates, an ancient Greek physician. Or so the story goes. Whether the phrase originated with him is disputed. But it does contain a kernel of truth. Walking is a form of exercise that is free, requires no equipment and is easy for most people to incorporate into their days. But how many steps should one walk-and at what speed-to unlock its benefits?

Conventional wisdom sets 10,000 steps per day as a good target. That source of that number, though, is as questionable as Hippocrates' quotation. Its origins lie not in a clinical trial, but a Japanese advertising campaign for a pedometer launched ahead of the 1964 Tokyo Olympics (10,000, in Japanese Kanji, also looks a little ...