In the picture above you see on the right a guy with nice posture, his head resting on top of his spine. When standing up straight this guy's vertebrae require no muscles to engage to prevent his head from falling forward. Now look at the guy at the left, his pelvis is tilted backward, which could be caused by tight hamstrings, and with a back tilted pelvis his lower back flattens, which requires his head to move forward to keep balance in the spine as a whole. In this case a lot of muslces have to engage even when this man is doing something as simple as just standing. No longer sits his head nicely balanced on top of his spine, no way, his head hangs forward and requires at least the muscles in the back of his upper back to continually engage and work.
A bulging disc develops when a vertebral disc bulges into the spinal canal, sometimes compressing a nerve in the process. Often referred to as a "herniated disk," bulging disks are technically a different and less severe condition.   Disc bulges occur naturally during the aging process. Many people have disc bulges in their cervical (neck) spine and never have symptoms or require treatment. A painful cervical disc bulge can be treated at home and by a doctor in a number of ways. It often takes time, changes in activities and exercises to heal it properly. Occasionally, surgery is also necessary.