Oxygen is one of the first elements we learn about in grade school. Humans breathe it, plants produce it, fire consumes it, and the higher you go the less you'll find of it. At Denver's 5,280 feet of elevation, oxygen and air density levels run about 15% less than at sea level. Doesn't sound like much? But consider this: an 8-minute/mile jogger's pace will slow to a 9:15-minute/mile with the same level of effort. A golfer who normally drives the ball 250 yards can carry close to 300 yards. And, a major league pitcher, accustomed to the air density's "grab" on a curve ball, will watch it break 25% less.
Golfers will be psyched and pitchers disappointed, but what can endurance enthusiasts do to minimize these effects? Many have researched the consequences of altitude, and most arrive at the same conclusion. During the first 24 hours in a higher elevation the body withstands any adverse symptoms, and after 7 days the body has acclimated. The interval in between is when you'll suffer the most, with day 1 causing minimal impact and days 2 and 3 exhibiting the most. Finally, on day 4 your body begins to recover.
So, if you plan to run in a thin-air marathon or compete in a high altitude soccer match, strategically book your travel plans. The Raiders are known to arrive in Denver as late as NFL rules allow. Soccer teams playing in Mexico City (7,500 ft. elevation) typically fly in less than 12-16 hours before game time. You may not have this professional athlete luxury, but just remember that the Mile-High City's altitude is a breeze compared to places like La Paz, Bolivia, where international athletic events are hosted at 12,000 feet!