Who knows, but has been discussed on the boards several times... (excerpt from a post on a past thread):
Luiz Oliveria is proably the best 800 meters in the history of the event uses a couple different hold breath drills with his athlets.
I'm no physio expert but he told be that is was a great way to simulate the amounts of lactid acid in your body during and in order to build up a tolerance this is what he does.
He does it in a couple different ways.
1)run a 100 meters like this
30m hold breath 5m breath 30m HB, 5 Breath, 30 HB
2) RUN 120
36M HB, 6 B,36 HB,6B, 36 HB
HERE IS FROM AN OLD POST
World-renown Brazilian track coach Luiz De Oliveira has trained champion runners like Mary Decker and Olympic gold and silver medalist, Joaquim Cruz. De Oliveira claims his breath-holding drill allows middle and long distance runners to improve their endurance by adapting to increased levels of lactic acid. "I have a breath-holding drill that I use once a week," says De Oliveira . "I try to drive the lactic acid up quicker than it would in a regular race. That way, my runners get used to it. What I have them do is take a running start, then inhale and hold their breath when they hit the starting line, then they run for 25 meters. They work on technique while holding their breath. When they reach the finish line, they exhale and breathe normally."
De Oliveira then has them jog back and do the same drill for 30 meters, then 35 - all the way to 90 meters. "Everybody's capable of holding their breath for a very long time. But you've got to do three of these sets. By the final set, you're going to become very very tired. It's hard to hold your breath at that point. But if you use my drill, you will see results."
De Oliveira has another drill where his 400 and 800 meter runners hold their breath for just the last 30 meters, simulating the end of a race when they're most tired. At this point, they have to pick up their speed and work on their form. "The most important thing you can do in the race," says De Oliveira, "no matter how exhausted you get - is to maintain your form."
Read more:
http://www.letsrun.com/forum/flat_read.php?thread=3236714#ixzz4ZBLdT5ai