Great link provided by Ozman. Don't know about the chambers themselves but quite a few top level athletes will train in thinner, and hopefully purer, oxygen higher area's. Boxers in So Cal, before a major fight , will train up in the mountains like Big Bear, San Jacinto mountains, etc. World class US track athletes have major training centers in the mountians of Colorado, New Mexico, etc. The metabolism will speed up and fat burning is increased, as is endurance. The oxygen debt tends to be better handled by the body cells than it would be at normal ground levels. Football players need a little adjustment when going to Denver for games. I'm sure this must hold true for basketball & baseball players also. There is a tribe of Mexican indians living in the higher regions of the Sierra Madre who have amazing endurance and can run for hundreds of miles as a almost a normal part of the lives, usually barefooted. It's how the body uses the less amount of oxygen for the maxium returns.
A couple of friends of mine went to the Inca temple ruins in Cuzco, high up in the Andes. First couple of days they had headache's (like a bad hangover) but after they got adjusted to the thin oxygen they felt refreshed most of the time. He and his wife both lost body fat in the 10 day's they were in the Andes. Probably due to the body's adjustment to handling the thinner oxygen and it's affect on their metabolism. First couple of day's they couldn't climb 10 minutes with out resting (their both athletes) but soon made up for that in no time once the ability to use less air became accustomed to. They also tried the coca leaf, which to them only produced a mild buzz. It's not too cool for the breath though. They said their breath could to stop a charging bull moose, in it's track, after chewing the leaf for awhile. Good Luck.
