He's (probably) lying. Normal walking speed is around 3mph per hour. 4mph is a very fast walk to a jog (more jog for peeps like Chris). He would be covering about 6ft/1.8m per stride (distance covered by "left" and "right" steps together) at 4mph. Assuming average-ish 30in/0.75m per step, he is taking more than two steps per second. Unless his fitness level has drastically changed since he "did" a "Parkay", I don't think this is possible.
Most gyms also limit cardio time to 30-60 minutes for reasons of courtesy.
Yeah, I was thinking that, too. A 4 mph walk is a 15 minute mile, which is a pretty damn fast walk. Even 3 mph is a pretty brisk walk. Doing two hours of that would be pretty intense for most in shape people.
