Just to provide some perspective on why even we "high altitude" guys keep mentioning altitude and making sure you're prepared for it....
(Aside from the fact that most of us have had some serious eye openers.)
If we call sea level our baseline with "100%" oxygen available, the following is available at these altitudes above sea level:
. 335 ft - 98.5% (Little Rock)
2,000 ft - 92.8%
2,500 ft - 91.4% (Ozarks)
3,000 ft - 89.4%
5,280 ft - 82.3% (Denver)
6,000 ft - 80%
7,000 ft - 77%
7,120 ft - 76.7% (Pagosa Springs)
8,000 ft - 74.2%
9,000 ft - 71.3%
10,000 ft - 69%
11,000 ft - 66%
11,570 ft - 64.6% (Vale)
12,000 ft - 63.6%
If you re-baseline with Little Rock as the reference altitude, Denver ends up at 83.6% of what you're used to; the atmosphere at Pagosa Springs provides only 77.9% of normal; and 10,000 ft won't give you more than 70% of the oxygen your body wants.
Short version:
At 8,000 ft, for example, everything feels 25% harder before you even factor in the additional energy and strength required to deal with terrain, ground cover, and snow/mud/rain.
It's nothing to be afraid of, and it won't kill, but you need to at least
mentally prepare for an acclimation period.
If you're in good shape, you'll probably fine after a day or two. It doesn't change the fact that your body is still working notably harder to get the same amount of oxygen; but you may not notice it as much.
On the flip side....
When you get back to Arkansas, you'll feel like you're breathing soup.
