Earlier articles with walking-speed vs death association:
2015:
“5 year mortality predictors in 498 103 UK Biobank participants: a prospective population-based study”. Excerpts related to walking:
– Self-reported health and walking pace were the strongest predictors in both sexes and across different causes of deaths.
– Our findings suggest that measures that can be simply obtained by verbal interview without physical examination (eg, self-reported health and walking pace) are the strongest predictors of all-cause mortality.
http://www.thelancet.com/jo…

2013
“Association of walking speed in late midlife with mortality: results from the Whitehall II cohort study.”:
– Slow walking speed is associated with increased mortality in the elderly, but it is unknown whether a similar association is present in late midlife. Our aim was to examine walking speed in late midlife as a predictor of mortality, as well as factors that may explain this association.
https://www.ncbi.nlm.nih.go…

Hat Tip and thanks to fellow reader John H. Newcomb who provided the quotes and links above in the comments section from the original article.