Narrator: This is Science Today. Excessive heavy lifting is known to harm the back, but Jeffrey Lotz of the University of California, San Francisco, says just sitting in a chair for a long period of time can also do harm.
Lotz: It's been shown in various studies that periods of inactivity can be as harmful to the back as periods of excessive activity.
Narrator: Lotz is studying how various mechanical loads affect the discs of the spine in an animal study - the first of its kind to demonstrate heavy loads actually alter the physiology of the disc.
Lotz: We think that this model will allow us to define, hopefully, a boundary of how much force on the back and the duration of either inactivity or excessive activity - which is beneficial.
Narrator: In the meantime, Lotz recommends moderate exercise.
Lotz: Your disc by itself doesn't have any blood supply, so there's obviously cells in the disc which need the blood supply in order to be healthy and part of the way you get nutrition to the disc is through physical activity and so you need a certain amount of force in the back to keep your discs healthy, but obviously, too much can be bad as well.
Narrator: For Science Today, I'm Larissa Branin