Creep in Mechanical model: 

Take a rubber band, stretch it and fix its both ends. Let it remain stretched for hours then observe what happens once you release the ends. You will be disappointed if you are expecting the rubber band to come to its original (Pre-stretch) length immediately. This effect is called hysteresis. In a nutshell, low load; long duration stretch will alter the property of any elastic tissue.

Creep in Human model:

 Since your muscle, ligaments, and fascia are also an elastic tissue like a rubber band, sitting slouch creates constant strain on your spinal ligaments, disc materials, muscle tissues and over the time it causes fatigue and laxity created by “viscoelastic creep”. 

Irritation and subsequent inflammation of deep tissue taggers reflexive contraction of entire low back muscles leading to ongoing involuntary back spasm.

The Interesting part of this story is, you are now prone to get a sudden severe back spasm when you try to bend your spine and pick up a pair of shoes from the floor.Most of the time a slouch induced creep is the culprit, not your forward bending action or weight of the object.

The saddest part of the story is, in order to reduce the pain you keep stretching the back muscles which is already over stretched.

The fact is you must do a lot of isometric back strengthening exercises then progress to lifting exercises.

Creep is nothing but stretching a soft tissue/elastic tissue over time which will change its property of elasticity and contraction ability. 

Sit straight!

Lift weights!

Cut the creep!

Prevent backache!