Flagstaff has long been a destination for elite athletes to train at high altitude. From swimmers at the Wall Aquatic Center to runners on the trails, working out at 7,000 feet can increase oxygen-carrying red blood cells by 4 or 5 percent. Now, new research shows the longer athletes train at high elevation, the better the results. Dan Bergland is a sports physiologist at HYPO2, Flagstaff’s high-altitude training camp.