After long rides my quads were hammered but nothing else. Hurt to walk up steps. After some research here and elsewhere on fitting, I moved my cleats back 1 cm so the ball of my (size 13) foot was > 1 cm in front of the pedal spindle. Man what a difference! I had more power and my legs were less tired and more evenly tired after the ride and my quads didn't really hurt the next day. It is amazing what 1cm can do for you!