Ellen, I had started to do a bit more speedwork recently, but had also been trying to focus on my gait, taking longer, slower strides (as advised in a running magazine) so maybe that's why. I have been doing the stretches recommended by Boo, above, for a week, and have no problems at the moment. Haven't done a long run yet this week, so will let you know after my 10 miler at the weekend! What treatment are you having?