The researchers say this suggests lower-back pain patients have an enhanced response to pain in some brain regions, and a diminished response in others.

BBC: Brain to blame for mystery back pain

"It's common with someone that hasn't done much running to get knee pain, back pain - any issues with their lower limbs, " says Harrison.

CNN: Prevention better than cure

On the other side are doctors, many of them pain medicine specialists, who believe narcotics can be used safely on a long-term basis by patients with problems such as lower back pain.

CNN: Facing chronic pain without drugs

The team studied 18 weight-related medical conditions, including cardiac disease, type 2 diabetes, cancer, stroke and lower back pain.

BBC: Overweight man measuring his waist