The 10,000-step rule likely began as a pedometer's name

A Japanese company launched a pedometer called the manpo-kei, or 10,000-step meter, in 1965, and the marketing figure spread worldwide as medical advice with no trial behind it.

Researchers at Brigham and Women's Hospital and Harvard Medical School tracked step counts in 16,741 women with an average age of 72 and found that those averaging about 4,400 steps a day had a 41 percent lower risk of death over the next 4.3 years than those averaging about 2,700 steps, with benefit leveling off around 7,500 steps.

Walking speed made no measurable difference once total daily steps were accounted for, undercutting the idea that steps have to be brisk to count. The study looked at older women specifically, and the exact useful number likely shifts with age, but it joined a growing body of work showing that a marketing slogan from six decades ago overstated what the body actually needs.

The number on the pedometer was never medical.