I'll keep that in mind, it'll keep my leg muscles in good working condition during winter.
My method of increasing speed over time, is keeping irregular short burst sprints. I don't know if it's healthy for the muscles in the long run.
For example, 10 second sprint followed by a minute or two of regular rhythm running speed. Over time, I increase the sprint time. At my peak level, 25 second is my average at keeping a sprint pace.
I've tried a full out 45 second sprint at peak level, but that just leads me to wheezing, and afterwards, barely able to keep a jog pace.