Here's a concept for you.
I was reading about the world records for breath holding. Those guys basically each morning, wake up and hold there breath for x amount of minutes and "Train" for this. What i find very intersted is the people that do this, have some of the most efficient hearts in the end, their average heart rates drop to the high 20's to low 30's.
So what i was thinking is, a study should be done to encorporate this into marathon training. If a normal Joe just trying to break a record for breath holding can get their body to be this efficient with oxygen and get their resting heart rate to 30 without exercise.. i bet it would definitely give some kind of big advantage to running in the end. The world record for holding breath is like 15+ minutes and is constantly being traded between a group of 3-4 people who keep breaking each others records.
Thoughts?