a) an elbow to the top of your feet always hurts, esp. when you're tired and you throw a sloppy kick.
b) after years of training and copping bruises, the muscles on your feet (or any part of your body for that matter), start to have tiny little tears forming. and because of the regular training they seem permanent.
Now when you bruise, the fluid for it will be any little crevice in your muscle to fill up, hence resulting in massive swelling ,when really some of the time it isnt that bad.
ive seen someones knee blow up everytime they do high-impact sports. it goes down into a little bubble, and then just fill up again.