Agree with JJ - You'll probably find your muscles are plenty warm enough, it's just the outer layer of fat which feels cold because it doesn't have the same blood vessels running through it - But the general numbness will make it feel as if your muscles are stiff.
I think women suffer from this problem more than men because we tend to have more fat - Hence why lots of men can still run in skimpy shorts in the winter but we're all lagged up in our long leggings.
I have to say, my legs were soooo freezing last night, even in long tights, and I wondered what else to wear on my legs to keep warmer - I did consider wearing a normal pair or ladies tights underneath - Has anyone ever tried this?
My top half, which normally warms up really well, stayed quite chilly for the whole run.
I'm glad I ran last night though - Don't fancy going out in the 6 inches of snow today.
J.x