Tuesday, December 11, 2012

How Fast Can You Walk? Part 2

So yesterday's study regarding gait speed vs mortality in the oldest old didn't come out quite the way I expected.  But then again, children aren't little adults either.  In other words, perhaps gait speed is a worthwhile measurement in other age groups.  In fact, in a meta-analysis of 9 cohort studies published in January 2011 in JAMA, the authors concluded that gait speed was inversely related to mortality in older adults.

In order to arrive at their conclusion, the authors followed for at least 5yrs (avg 12+yrs) 34,485 community-dwelling elderly avg 73.5yo (over a decade younger than yesterday's cohort).  To further differentiate these two studies (and perhaps explain the different outcomes), it should be noted that the oldest old (>85yo) were not even represented in one study and comprised less than 5% of the participants in each of 4 studies.  In only one study did this age group reach 17% of the total number of participants while 2 other studies and 11% each and the last had but 8% in the oldest old.  Truly, this study involved a very different set of participants compared to the Leiden 85-plus cohort.

Average gait speed in this middle old group was an impressive 0.92m/s which would have placed them in the fastest when compared to those a decade older.  More importantly, while gait speed ranged from as slow as <0.4m/s to as fast as >1.4m/s, the authors were able to demonstrate a statistically significant 12% improvement in survival for every 0.1m/s faster gait speed in those young old & middle old.  If you look at the Kaplan Meier survival curve, you'll see a compression or loss of benefit w/aging, which is consistent with yesterday's finding that gait speed did not offer a statistically significant advantage in predicting survival in the oldest old.

Bottom line: use the proper measuring tool that's appropriate for the group in which you are interested.  In this case, use gait speed in the young old and middle old vs ability to perform instrumental activities of daily living in the oldest old as a means to predict mortality and its inverse, survival.

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