I believe.

I did a century about a month ago. It was chilly when I started - around 50 degrees. I had on a light jacket, but just bib shorts. At about the 35 mile mark I started having problems with my left knee. I *think* it was ITBS (ilio tubial band syndrome) caused, or maybe just helped along by the cold. ITB is fascia tissue that extends from the hip to the knee, and when it gets tight, it rubs one of the bones in the knee that it passes over. I finished the century (tahnks to some Advil) in pretty good form, but in addition to stretching more, I'm going to heed that rule (although maybe at a lower temperature).