Your wrist counts every step. A 2.4-meter walk still predicted survival a bit better

On one side, a nurse with a stopwatch timing someone's walk over a 2.44-meter course. On the other, a wrist accelerometer worn for nine days, recording cadence, or steps per minute, through ordinary life. Which tells you more about survival?

Researchers tested both in 4,067 Whitehall II participants, average age 69.3. They followed them from 2012–2013 for a median of 11.8 years; 739 died.

Faster clinic walking speed, typical everyday cadence and peak cadence all went with lower mortality after accounting for other factors. All three ranked people about equally well. But only the clinic walk significantly improved prediction beyond standard risk factors. It nudged the C index, a score of how well a model sorts people by risk, from 0.742 to 0.747.

That is a small gain. The two kinds of walking also lined up weakly, with correlations around 0.27–0.28. A deliberate walk under observation and everyday walking seem to capture different parts of mobility. An accompanying commentary suggested using clinic speed as a first-line measure, with wrist data as a second layer.

The study is observational, so it can't show that walking faster changes anyone's odds. Participants were mostly White (92.5%) and male (74.4%). The accelerometer group was healthier than the wider cohort, and there was no outside dataset for validation. There is no agreed method for measuring cadence from a wrist. Could a better tracker measure close the gap?