When I was much younger, I used to have a small gym in the basement, like who didn't? Well I was benching, feeling strong and kinda of bouncing the bar, only 150 lbs, but I was only 16. Very dumb move. My chest was soar for weeks till I went to a Dr. and found I'd cracked my sternum. It healed just fine, but when you're young and invincible.......and I wasn't bouncing it hard just a little more than a tap, I thought. The lesson.....Never bounce the bar off your chest. I cringe, but don't say anything, when I see guys bouncing multi plates in the gym. They'll learn.