Discs have pressure in them just like a car tire.
When you lay on your back, the pressure inside a disc is 25 lbs/sq. inch.
Standing is 100 lbs.
Sitting jumps to 140 lbs.
Bending from the waist without bending your knees is 150 lbs.
Seated slouched is an amazing 200 lbs.
http://ow.ly/i/1sngx