A Slouching posture can increase pressure on our discs and stretch the ligaments and other soft tissue structures at the back of our spine.
Arching back and sticking out our chests is not ideal either. This military style position increases the pressure on the facet joints which are at the back of our vertebrae. It also is associated with increased tension in the muscles that run either side of our spines.
The ideal posture is to have our lower back and pelvis in a neutral position. This is the mid position between slouch and excessive arching. Secondly try to have your ribcage aligned over your pelvis. Your head position should be such where your ear is over your shoulder.