it could be that there's less fat to cushion them, or that the vessels are closer to the skin surface now so they are more likely to break if knocked...or maybe now your circulation has improved so when you knock yourself, more blood pools there making more bruises? Im not sure
Maybe if they are really painful you could try a bruise cream. My fav is antiflam (its in a purple pot, smells like pepper mint, and makes the skin go hot, then really cold, and then its heavenly
)