For me, it’s definitely the uniform! Decades ago I got hooked on distance running myself and ran a half-dozen marathons, and besides the shorts chafing even the pinned race number would get annoying on my chest. He’s added a slew of chafe points with the garb, but might not get too raw from a half.
I figure the roller could roll on all fours by his side and offer maybe the slightest arm rest if needed. 
Great story and best wishes to John Bird.