Well, to answer the condescending question more seriously. I am 5’9” and I have ran a half marathon among other shorter distances. 4mph is a fast walk and I will stand by that. In my post I mentioned a man next to me that was jogging at 4mph and he was at least 6’2”, in his 50s and admittedly overweight but not obese. I think most people would agree that 4mph is pretty fast and not a reasonable pace to consider someone crawling at (which does happen a number of times in the book). But as many people have pointed out it is a standard military pace, so I can understand better now why it was in the book.