Well this is a first to me, I thought I would do a bit of cross training so went up to join my local gym, whilst there I went for a swim and did 30 lengths breaststroke. This morning I've woke with very sore knees, far worse than from any running I've done, so of course I googled it and found swimmers knee. Looks like I'll have to abandon this idea and just stick to running. Never thought swimming would hurt me, damn. Think I'll ditch the gym idea now as well.