Best Back Pain Exercises

i’m an active sport person. I used to have spontaneous pnuemothorax. Once in a while I still have chest pain during exercise, it feels different from the pnuemothorax which I once had. I was scared for re-occarrence, so I went for doctor and X-ray. It reveals nothing, but I still experience the chest when I’m having intense jogging or cycling.

Anyone experience the same problem? How can I prevent it? Thank you.

There is a constant pinch halfway up my back (a few inches below my left shoulderblade) which I attribute to hours of band practice with a sousaphone on. I always stretch and warm up every day before I ever put it on. I don’t doubt that the first thing that falters when marching for so long is my posture and I suppose that contributes to my back problem. What else can I do to help ease the pain in my back, and prevent this from happening in the future?