High Altitude Training

I disagree a bit. I live at 4500' and find it beneficial when racing at lower altitudes. For short, hard efforts you'll get more benefit from training at lower altitudes for the reasons mentioned above but for most endurance training the benefits of training higher are great. Increased red blood cells, oxygen carrying capacity, etc. all help with endurance.

If I remember correctly, this depends on what counts as "high". Living and training at 5000' is as beneficial as everybody assumes. It's when you get much higher than that, say, above 10,000' that it might be better to live high and train lower. 

At least, I'm banking on this being true. I'll be spending much of the summer in Boulder, so I'm hoping to knock out some quick times once I come back down to sea level.

Agree or disagree, it doesn't change the science.  Even though the benefits of living high and training high (what constitutes "high" is also debatable) is still controversial, living high and training low has demonstrated measurable benefits.  Here are 2 studies about it:

http://www.sport-fitness-advisor.com/altitude-training.html

http://journal.shouxi.net/qikan/article.php?id=365925

The science (as stated in the articles) is generally inconclusive. The studies mentioned back up what I said regarding shorter, more intense efforts and also used elite athletes as test subjects - which most of us are not. Increases in VO2 max are great, but most people race at tempo or slightly above paces.

Regardless, I've seen many good athletes suffer at higher altitudes because they weren't acclimated. Living and exercising at higher altitudes hurts top-end (sprint) speed but I've found it helpful when racing at any altitude.

I wasn't saying that there are no benefits to live high/train high.  In fact, I said it's still controversial, meaning it's still an open issue as to how beneficial it is, not whether it's beneficial or not.  My point was that there is more evidence that live high/train low is beneficial, so going with that method (if you live in a location that makes it possible), is a better bet.

You do make a good point about studies performed with elite athletes, though.  What works for them doesn't always have the same impact on the average age-grouper, so YMMV.

I spotted this awhile back:

http://www.twowheelblogs.com/how-altitude-affects-power-output

Unfortunately he doesn't cite the studies.  But in practice it seems a fair assessment from what I've been able to do in different locations.

But another thing people forget is that altitude also plays into aerodynamics.  Go over to analyticcycling and play around with the numbers for air density.  It's somewhat amusing when you discover that your drop in power at altitude doesn't necessarily reduce your speed (because of lower air density).