The following is a guest blog by e-Outdoor:
Rocky Mountain National Park starts at an elevation of about 7500 ft. above sea level – or about 1 ½ miles up. Aside from the breathtaking vistas and the crisp pure mountain air you'll find at that elevation, there are some effects on your body caused by the elevation. Everybody has heard that the air is thinner at higher altitudes, but what does that actually mean?
25% less oxygen in the air than at sea level. This reduction in oxygen will have some effect on everybody and produces very uncomfortable effects on some.
To avoid altitude sickness at this level the key is acclimatization prior to strenuous exercise. The body adapts quite well at this altitude and reasonably quickly. A single day at a relaxing pace is a huge benefit if you're from a more typical area near sea level location. Within 4 days the body of most people is fully adjusted to be comfortable at this altitude. Across a few weeks your body will actually adjust the composition of it blood to adapt completely. Since most vacations tend to be in the 7-14 day range, that is what our concern will be.
When first arriving at Rocky Mountain National Park, particularly with a flight in, then a rental car up to the park, your body has had very little time to adjust. The immediate response is faster than normal breathing and a tendency to breathe shallower. Some people may experience altitude sickness in the form of mild nausea, rapid breathing and heartbeat, or headache, simply from being at the altitude. If it persists more than a few hours, or is more than slightly uncomfortable, try driving a couple thousand feet lower in elevation for a day or two then return to the park. Most people will not need to do that, however.
Spend the first day in the park at your campsite resting. Do not plan any hikes or strenuous activities for the first day. Drink extra fluids as well. If you want to do a long or particularly arduous hike, save it for at least 3-4 days into your stay so you'll be better adjusted. Since it takes weeks to completely adjust, you will never be able to do the same amount of exertion for the same period of time on your trip as you could at a lower elevation. Use that knowledge to plan additional time for hikes and activities. If you could do 8 miles a day at a lower elevation, plan 5 or 6 miles at this elevation.
Along with the lower oxygen comes lower temperatures. A typical jacket or cold weather gear for the season will not be adequate at higher elevations. Alpine rated outdoor gear is available from e-outdoor and other places that is far more suitable for the altitude you'll encounter in the Rocky Mountains.