The tissues in the back actually need some tension in order to support and stabilize the spine. This tension provides a stiffness that protects your vertebrae as you move. If the tissues become lax, the vertebrae lose stability, making them prone to injury.
Researchers have shown that keeping the spine bent forward for long periods causes a loss of tension in these tissues, which makes the spine loose and unstable. In this case, a lack of tension can actually set the stage for back injury.
To allow these tissues to recover during the workday, use good body postures and take frequent rest breaks.