Thread: Why is there bruising on knee's after leg workout?

This is for my brother. He had a good leg work out and pushed some good heavy weight. A couple days later he had a big bruise on his knees. After he works out he uses a stick roller to massage out the body parts that he works out that day. Could it possibly be from pushing all the lactic acid towards his knees and not pushing it all the way through where it wouldnt just stop at his knees? or is it something else? Is this normal/common? What are ways to prevent this from happening?

Sounds like he was putting alittle pressure on his knees during power cleans :-/ Hope it isnt to bad dude.