Envision the Hamstrings as a continuation of the spinal muscles that run along each side of the spinal vertebrae. And the hip flexors a continuation of the spinal muscles that run deep in the front of the spine. As an individual sits for longer periods, these muscles remain shortened and cause corresponding changes in the spinal muscles in the back. The stiffness most folks experience upon standing is due to this situation where the length:tension ratio of these partner muscles is out of proportion, therefore not allowing the joints of the low back to move properly .
So to compensate for this temporary dysfunction, the body recruits other muscles to help pick up the pelvic girdle and allow the hip joint to properly function. This recruitment pattern in movement exposes the low back's vulnerability to strain