Symptoms Update (Riding my bike)

OK, so another brief post in the never ending list of things which may or may not be relevant.

I cycle to work. Its 6-7miles each way (10-11km), and I can do this in about half an hour. In the last few weeks I've been noticing that my feet gradually move forwards on my pedals as I continue my journey. I wonder if my quads are getting more tight, preventing my knee from flexing quite as far on its way back.

I cant work out if getting some SPDs would be worth a try, or if thats going to turn out to be more trouble than its worth.