It looks as if I'm several years late coming to this very informative post. I just want to add the following quote from Running with the Legends (p177) referring to when Viren and a teammate went to Kenya to lay the foundation for the 1972 Olympics:
"All they did was run, eat, sleep, and run some more to get ready for Munich. A typical day included a morning run of 1-1 1/2 hour, then breakfast and a nap, followed by another run in the middle of the day, then more eating and sleeping before an evening run. Viren followed this Spartan regime for three months, running as much as 200 miles a week..."
I was also amazed at the extremely low heart rates reported during some runs, i.e. 96 BPM during a 25K run, 84 BPM during 12K, 90 BPM for 17K, 84 BPM for 15K, etc. The rest of the reported heart rates were between 122 and 180. I wonder what Viren's resting and max. HR was?