I did something a little different on my run today--started out with about 25 minutes of my normal (rather slow) trail running, then did 7 or 8 short sprints (I don't think they were even 100 yards) with walking in between on an open section of trail that runs alongside power lines, then ran normally back to my starting area. Altogether, I was out for about 45 minutes and felt pretty good other than the expected huffing and puffing from the sprints . Maybe I'll work in some intervals a couple of times a week and see if it makes a difference in my "cruising" speed.