Well not all that high really - 4000 feet, in the town of Moab, Utah.
But nevertheless, all of my running over the past year has been at around sea level. I don't know whether it was the altitude, the spasmodic nature of my runs over the last month, the eating and drinking while on holiday over the past month or the new low drop shoes that I bought here. - but the 30 minute run didn't feel to be one of my best. On to Denver today - but that is much higher and they are predicting snow tonight. I don't do running in the snow!!