Actually... I find running in circles quite preferable to running on the hamster wheel that is the treadmill. Though it still isn't optimal, there *can be* enough variance in a 1/6 or 1/8 mile track to help a person make it through a medium distance run. Though I have found 6 miles is probably my limit.
An interesting side-effect of the track running is "accidental speed work." I found that After running 6 laps, I could spice things up by sprinting a lap. So I ended up putting in some speed work (which is not my strong suit.) on a day when I just really intended to be out and running a simple 6 mile easy pace. Hooray for happy accidents.
As I have about 10-12 speed workouts as part of my marathon training, it's nice to know that one won't kill me.
Here's a chart...
The little plateau around 37:30 was a little experiment in trying to achieve the fastest cadence/turn-over that I could by shortening my stride and taking quicker steps. Interestingly, while the cadence got to just above 180 steps per minute, it was nowhere close to my spring cadence where I was sprinting and not taking purposefully shorter strides.
Anyways... can't wait 'til the weather breaks.