I will be going to Denver on a business trip in early September and I am planning to run a 10k race there. I live in Houston and have never run in high altitude cities like Denver.
Is there something that i need to take into consideration regarding the altitude? i will be there beginning Wednesday and the race is on Saturday so at least i will have 3-4 days to adapt to the altitude.
Basically, the air is thinner, therefore less oxygen, so you won't be able to run as fast, as easily. I have no personal experience with this, but I've seen folks post that you can do some adaptation in about a week. OTOH, the "experts" say it takes several weeks to become fully acclimated. I would guess that Wednesday to Saturday will let you get used to how fast you can go, but I doubt you'll be able to run as fast.
I live at relatively low altitude - Los Angeles - but have traveled to Denver and other cities at comparable altitude (e. g. Albuquerque) a number of times. At rest, you may not notice the difference between ~5200 ft and sea level. However, on running, you will need to breathe appreciably harder, compared to sea level, for the same running speed, and you will max out at a slower speed than at sea level. As Len noted, because the air is thinner, you're getting less oxygen with each breath. My experience is that I'm about 30 sec/mile slower in Denver than in Los Angeles, at least for the first few days. I've stayed in Denver up to about a week and find that is not enough time to fully adjust to the altitude.
P. S. The air at high altitude often tends to be quite dry, so also pay extra attention to hydration.
@ 5K: New Balance Palm Springs 5K, Palm Springs, CA, 24:32
Angels Baseball Foundation 5K, Anaheim, CA, 24:24
Pride of the Valley, Baldwin Park, CA, 24:28
@ 10K: LA Chinatown Firecracker 10K, Los Angeles, CA, 52:15
Great Race of Agoura - Old Agoura 10K, Agoura Hills, CA, 51:40
Fiesta Days Run, La Canada, CA, 49:57
Back in 1990 I was living in Chicago and doing most of my training along the lake front (elevation 580'), and then a friend of mine invited me to join in the Mammoth Lakes Triathlon (which was an Olympic distance back then, i.e. 1.5K swim, 40K bike, and 10K run). The swim was in Crowley Lake with a surface elevation of 6,781', the bike ran from the lake, down and then back up and over Sherwin Summit where the elevation is only 6,426', prior to turning around and heading for the town of Mammoth where the elevation is 7,880'. I don't remember the exact course of the run, but someone told me we made it up to 9,000' prior to looping back around to finish in town.
I told you that to tell you this; I gave myself three days to acclimate to the elevation, and it wasn't enough. I'm not a strong swimmer, and through much of the swim I felt like I was one missed breath away from drowning, the bike didn't really feel all that much different (except for the climbing, the "hills" on Lake Shore Drive in Chicago don't really prepare one for the high Sierras), and then there was the run, yes, I was seriously sucking wind throughout most of the 10K. In the end, it took me some 25 minutes longer to do the Mammoth Lakes Triathlon than it did the Sun Times Triathlon that same summer.
My advice to you, run a couple of short and relatively slow 2 or 3-mile runs your first day there, push a pretty hard 5-miler your second day, go back to an easy 3 or 4-miler your third day, and you should be ready to race, albeit at a slower pace than you'd run in Houston.
Fat old man PRs:
I live in Denver and I see the altitude affect people all the time. Especially endurance athletes.
Spending time here and letting your body adapt is really the only way to get use to the altitude. How long does it take? Depends on the individual and what your body is use to. Do you come from an altitude of 1,000 ft, sea level, etc? Many studies I've read say that it can take up to 2 weeks until your body fully adapts. (Again, this all depends on the individual).
If your looking for a great place to run in Denver. Check out running in Wash Park.