Folks, trust me, if it were possible to run for 2 hrs every day in one stretch then a lot of runners would do it, but unfortunaly (or fortunately, as the case may be) runners can only tolerate limited pounding. That is the nature of this sport. It is not like swimming, cycling, cross country skiing, and other endurance sports where there is no impact.
The limitation of running is the impact, and that is why cross training is good for most athletes, because they can augment their daily dose of aerobic training with other aereobic activities.
The maximum that top runners can run in a single stretch, day after day, for months on end is usually around 1.30 minutes or 15 miles or under. Anything over that, and you start to break down. Many athletes break down with less time or distance than that.
When University of Colorado athletes did most of their mileage in singles, only the strongest on the team survived, and there were always a lot of injuries.
For most athletes, an optimum time frame for running a progressive run would be between 40 to 60 minutes. Those who have high aspirations can run twice a day, with the same time frames, but one of the runs should be easier, much less taxing.
It also does not pay to run fast every day. It may work for a while, but those athletes who train like that, tend to have shorter careers (Ron Tabb, Derek Clayton).
The best athletes are able to go slow when necessary, and we can learn from the Kenyans with this, as they start all their runs (jogs) at a very slow pace, so slow in fact that any jogger could keep with them for the first mile or two or even further on some runs. They seem to be able to gauge how to treat their bodies.
The Japanese are also good at slow running and walking when required. Running/jogging machines, they are. When going easy, they run for time rather than distance and that is the way it should be. Jeff Schiebler (13:13/27:36/2:14) did not like that aspect of training in Japan, and he was given a waiver to not run the early morning slow jogs with his Japanese teammates.
Western runners tend to be more competitive on training runs, and often get down to 6 minute pace within a few minutes of running (too fast!).
Ghost in Korea