Running

I've been doing interval walk/run stuff on the treadmill. I set the walk to 4 mph, and then I gradually increase the speed of the run segment over the course of 30 minutes. Today, I kept the run segment at a brisk walk just short of a run for the first 10 minutes (4.3 mph), then up to 5.5 during the next 10 minutes and then 6+ for the last 10 minutes. I reached a new top speed of 7.5 mph!!! OK, yes, it was only for 2 minutes. So sue me. But still - it actually felt easier than I expected in my legs, though I was breathing very hard.