Over spring break, I was on a caribbean cruise and since my Xbox 360 nor my Dance Dance Revolution mats were near by, I tried to go running on the treadmills. It went better than I though! I ran about 4 miles over 40 minutes each time. Not great, but better than most. However, I tried going running here back in Oklahoma and it was much harder for me. I wonder if there's just that much more oxygen at sea level than at 1174 feet above sea level, or maybe if I'm doing something wrong. Any ideas?