Yesterday my gf and I completed a 73 mile ride on a route that stayed around 5000’. I’m hoping to attempt my first century this fall on a route that will probably not exceed 500’. Would my performance at 5000’ indicate I’m likely already prepared for it?

Well, you're ready now, but who knows where you'll be in the fall. Stay healthy and ride. Best prep ever is riding 60 mile hilly routes once a week. High altitude performance isn't much of a predictor of anything because lower O2 levels also decrease muscular output. Sleep high, train low is the mantra. That said, 73 miles at 5000' is all to the good.

Just like riding a heavier bike for training rides then switching to a light bike for a race, you'll definitely feel better about it. There are still a lot of other things that might make your performance numbers not much better. One of them being if this is the only long ride or even short ride you do between now and the fall.

My son lives just outside Denver now. When this COVID thing is done or they get a vaccine, I'm looking forward to going out there and seeing what it's like to cycle there at 5000 to 6000 feet. However, from my flying days in unpressurized aircraft, I never thought 5000 feet very high for physiological stuff.