Running can make your thighs bigger rather than smaller

This is my fourth consecutive day of running now.  I am not going that far each day - 10km max, but it is nice to get myself moving and burning off some calories each day.  Actually in terms of the number of sessions, I am actually doing more now than when I was preparing for my marathon or preparing for La Marmotte.  When I was preparing for my marathon I kept having to rest due to runners knee.  Then when I was training for La Marmotte I tended to only cycle 3 times per week.  I don't think I will get as many problems now with my knee because the muscles around my knee are much stronger now, and also more flexible through regular stretching and massage.

Thunder thighs

What I am surprised about though, is that in the last 4 days I have noticed my thighs are starting to grow.  This may be temporary but I find often that when I do a lot of sport and the distances are not really large, I tend to bulk up.  If I want to stop my thighs from growing even more I will probably have to start running longer distances again.  I think once you get to a certain distance your body realises it is inefficient to have large bulky muscles and starts converting them to lighter wiry ones instead.  It will be good if this happens as there will be a lot of hills to climb in South America, and power to weight ratio rather than raw strength is what counts.