Great questions! Training at altitude - or "hypoxic" training - can be very beneficial, but the biggest benefit you get from living in Colorado is by sleeping at your 5400 foot elevation. In an ideal world you'd sleep high and train low to get the biggest bang out of your training.
Sleeping at a high altitude means your body has to work harder to deliver oxygen to the muscles due to the lowered oxygen concentrations.
This causes the body to adapt to the stimulus and create physiological changes which are beneficial (increased red blood cells, increased blood volume, etc.). However, sleeping at altitude is not always an advantage as the reduced air pressure also means your muscles do not have sufficient oxygen to recover from hard workouts. The use of altitude chambers as a training tool for bed time can be cycled for maximum advantage. You want to sleep at high elevations long enough (usually at least two weeks) to allow for enough physiological adaptations, yet you also want to sleep at a low elevation in the final days leading up to a high priority event so you can maximize your recovery and race with a completely fresh body.
The altitude at which you live, 5400ft, is on the lower edge of where reduced air pressure makes a difference in performance. So your sleep at night is helping you get faster for sea level competition. I assume you train above 5400ft and this can be beneficial especially if you are concentrating on longer events and climbing mountains in Italy like you talk about.
The big drawback to training above 5000ft is it is harder to maximize your muscular system because you always have a ceiling on how much oxygen your body can deliver to working muscles. There is a loss of about 8 to 10 percent of aerobic capacity for every 3300 feet (1000 meters) of elevation gain above about 3500 feet.
You will probably benefit from your time in Colorado due to higher blood volume and other adaptations (higher red blood cell count, etc). But there are many variables (hydration, diet, training, etc.) and each individual adapts differently.
It's well established that going from sea level to altitude causes the body to produce more lactate in the first few days before adaptation takes place which should then cause the lactate threshold heart rate to be lowered somewhat from what it was at sea level. This might imply that going to SL for someone who is altitude-adapted might cause the body to produce less lactate, at least for a few days, at a given level of intensity.
Good luck in your training
Joe and Dirk Friel
Google that shit
http://www.google.com/search?hl=en&...d=1&q=high+elevation++muscle+training&spell=1
