The main set of my workout today called for 5X50yds, 50 second lap with a 10 second rest. I had to do that twice. I was able to *just* make it on the first set, but had to extend the rest to 15 seconds on the last 2 laps of the second. When I was with my coach, at the pool in Carson City, elevation 4500 feet, I did the laps in 47 seconds. Here, at 6000 feet, it was all I could do to hit 50. It's just amazing how much the altitude affects swimming.