I know it's a big question but i'm a guy who tend to sit all day long on a chair, sometimes without a great posture, arching my back and not sitting straight.
I want to know if there's a key exercise to regain a good posture. Also what are exercises to gain flexibility?
I've look on the internet but there is so much information everywhere don't know where to start. Maybe if you have exercise that target the back at first, that would be a great for a beginning.