Help! I can't get the stink out of my son's Under Armor.

My son played football and wore Under Armor under his uniform. I always washed it with detergent after every wearing, and hung it out to dry on the clothesline. He is now running track and needs it for the colder days under his skimpy track uniform. The problem is that it stinks like BO really bad no matter how many times I wash it.
Is there some special hint to getting the perspiration smell out, or will I have to throw it away and start with new. It’s made from 81% Cationic Polyester and 19% Elastane.