Race Into Shape?

My main goal (for the spring) is the Illinois Half-Marathon on April 22 (8 weeks to go!). Training has been going well, but I still have to work on my stamina and speed. I already have the basic endurance. I think a couple of races over the next 6 weeks might help me focus and test my speed.

My first test race will be a local trail 5K on March 12. It's the "Pi Mile" run in honor of Pi Day (which is actually 3-14). Working in engineering, this seems like a great fit. And the local University Arboretum provides a nice course. Perfect test of my VO2max.

Three weeks later, on April 1st, I have two race options. Another 5K (this time on roads and bike path close to my house) or a trail half-marathon at a park about 30 minutes away. The "Run for the Library" 5K would be super convenient and allow me to see my progress on speed from the trail 5K three weeks earlier. On the other hand, the Allerton Half-Marathon will let me challenge my stamina on one of my favorite park trails. The Allerton race also has a 10K race option. I suppose that might be an ideal distance to test both speed and stamina...but who runs the shorter race option?

For now, it's the March 12 trail 5K (Pi Run). Depending on how that race goes, I'll decide on Run for the Library or Allerton trail race. Any suggestions on what option would be best for the second race?