OK, I just moved from Placitas NM to Fort Worth TX -- from 6k ft altitude to a few hundred feet. On top of that, I moved from roads where hills where constant (either up slowly or down quickly, lots of long 10+% grades) to roads that are fairly flat. I have been using my HR monitor during training and for racing, but even with doing sprint intervals my legs start to burn like crazy and I hit fatigue failure before my HR goes much above 70%.
So, short of finding something new like a stairmaster or running, any tips on keeping my cardio fitness up? Or is this just something I sacrifice and pay for next time I'm riding at higher altitudes? (Enjoy it while it lasts?)