I've been running a bit these last couple of weeks, although with some trepidation since my thyroid situation isn't yet sorted out. Yesterday, I ran a mile on the treadmill and then did another 20 minutes or so of hill and speed intervals. And by speed, I don't mean spring, just a bit higher pace than what I typcially run (7 mph versus 6). I have absolutely no knowledge on how best to structure intervals though, so I was doing a minute off (walking) and 90 seconds on.