The diagram shows how a flat back posture can squeeze the front of the vertebral disc and could cause disc problems.

Flat back posture often puts more strain on the vertebral disc as the person's body weight tends to be slightly forward. There can also be increased muscle strain as the lower back muscles have to work hard to hold the person upright.

A person with this posture typically bends from their spine when reaching forward and therefore fails to engage their gluteal  muscles. The overuse of the back muscles can lead to fatigue and muscle spasm.

It is therefore important to improve muscle recruitment so that the work being done is shared by several different muscle groups as opposed to just the lower back. 

The section below details which muscles could benefit from being stretched and which ones need to be strengthened.