How can i strengthen my sternum or also known as "the puke spot"?

okay im a boxer and we are doing body conditioning. and i have my hands up and im getting punched in the sternum 3 times in one go really fast and hard and it makes me loose my breathe and makes me gag like im going to be sick. I know its a bone, but is there muscles around it which i can develop with certain exercises to act as body armour while im being punched in the sternum (puke spot) thank you guys ?