You could also do midweek speed workouts. Like 400m or 600m repeats.
I'm trying, but it seems like every time I hit a track I strain my hamstrings where they attach at my butt. I've dealt with that for a number of years now and I get to where I think I'm good with it, then I go to a track and get hurt. But you're right, I do need to try that again. My training has been 1 day biking (about an hour), 1 day running (about an hour), plank for two minutes, limber up ten minutes on the vibration plate and 20-30 minutes in the sauna before going to bed. Not much else....