My personal best at that distance + 2/10ths was 2:48:45. Never tried to walk it, though!
With a mastadon chasing you, might be able to beeak that personal best. ;>)
But re: JFK’s physical fitness program occurred in 1960-62. Nobody then thought of running marathons except for a few Olympian candidates and then as solo training not the mass events of today. Non specific athletic shoes were Keds, etc.
In any case, my remark was to show that the “one mile a day” prehistoric chap as capable of covering far more ground on a daily basis if needs must.