When I was younger I could play the guitar all day without back pain (muscular). I stoped playing and exercising for many years, this with associated weight gain. Now I wanted to play the same guitar again but back pain do not allow me to it anymore (every 5 min I have to stop). I want to know if there is solution, and if exercise help. What is the best practice to strenght my back and be able to do what I used to do. There a detail, my sleep is not very good (few hours) and I can`t change this.
Being in shape helps prevent back pain. Being out of shape, overweight, and inactive all contribute to the problem.
I would lift weights at least two or three times a week, focusing on barbell squats and deadlifts, which are both tremendously helpful for strengthening the back. Yoga, going for a medium-long walk, or another form of stretching that you enjoy would be good to do on days you don't lift. It would be fine to add running, swimming, biking, rowing, or another form of cardio once or twice a week, to help lose weight. The primary problem is probably a weak back, however, which is best addressed with a barbell.