This is literally unfathomable to me. This guy has to be some sort of serious genetic freak. I workout regularly, but I think I just got chin splints just from reading that article. When you consider how even the most elite athletes fall victim to overtraining, I can't even imagine how his body was able to hold up to this. Truly amazing.
There's a theory from the latest TED talk that says our survival prior to inventing weapons (like spears) depended on running other animals to exhaustion.
The San Bushmen in the Kalahari Desert still do this today. This BBC clip on persistence hunting (narrated by David Attenborough!) is worth a watch; their endurance is absolutely incredible: http://www.youtube.com/watch?v=826HMLoiE_o
Sorry to be a snob but it's not a recent theory, I heard about something like this (men being able to sweat and run long distances, being scavengers, competing with hyenas) about 25 years ago.
"This guy has to be some sort of serious genetic freak."
Doing it every day would be very difficult, but doing it six days a week wouldn't be that hard. The term 'overtraining syndrome' is actually a misnomer, because you don't get it from training too much, but rather from chronic glycogen deficiency. As long as you eat a banana or an energy bar every 45 minutes and drink diluted gatorade you'd be fine with that workload.
The biggest concern would definitely be joint problems and not muscular issues. The reality is that this guy probably did do a lot of damage to his body, but was able to mask it using an anti-inflammatory/analgesic drug like ibuprofen or marijuana.
