Researchers who followed the health of nearly 500 older people for almost a decade found that those who walked more quickly were less likely to die over the course of the study.The findings, the researchers said, suggest that gait speed may be a good predictor of long-term survival, even in people who otherwise appear basically healthy. The study was presented at a conference of the Gerontological Society of America. ...
The study presented at the conference reported that nine years after their gait speed was measured, 77 percent of those people described as slow had died, 50 percent of those considered medium and 27 percent of those considered fast.
Which is cause and which is effect? I don't know, but I'm pretty sure that I walk "slow".
(HT: Nick.)
Walking fast will just make you die tired, but if you walk too fast, you will be too tired to die.