Good short article. I've been following Ken on Strava/IG for several months. He does his daily 10+ mile runs at a fast pace for a 51 year old, usually averaging well under 7 min per mile. Before his last marathon, his final big workout two weeks prior was something like 22 miles at 6:05. Kind of makes me think of top triathlete Kristian Blummenfelt, who is also also stocky but just goes and goes.
He's very strong across his whole body. I don't know if he could run as fast as he does if he was any lighter, but he's got wheels for sure. I think he races marathons in Alphafly (not that it makes any difference one way or another).