How Much Does Sunlight Slow You Down?

Well I've had a little over a week to reflect back on my Boston performance. Going into the race I was feeling good and I tried to learn from other runner's mistakes with Boston in not going out to fast. If you look at my pacing for the first 5 miles of down hill I was running a reasonable pace. My mid race pace was comfortable as well but as the day progressed I felt like I was starting to overheat. I was dousing my self with water at every hydration station. When you look back at the temperature that day it was not considerably hot (18 to 20 degrees C). I did end up with quite a sunburn on my neck arms and legs. The weather this spring was so cold that I did not run in shorts outside at all in the months leading up to the marathon. Last Friday, I came across this article from Alex Hutchinson that made me wonder if it wasn't so much the heat but the sun that affected my day. "How Much Does Sunlight Slow You Down? Temperature and humidity matter, but don’t forget about solar radiation."