Mom's repeated exhortation to "sit up straight" was actually bad advice, a team of Scottish radiologists showed yesterday in research presented at the annual meeting of the Radiological Society of North America in Chicago.

They used a special MRI or magnetic resonance imaging scanner to look at the pressure placed on the spine by various seating positions — a forward slouch, a 90-degree angle and a relaxed position where the knees weren’t at a right angle to the floor and the back was reclined slightly.

The scans showed that sitting at a 90-degree angle puts unnecessary pressure on the disks of the lower back, which can lead to back pain, disk degeneration and sciatica.

One of the authors, Dr. Waseen Bashir of the University of Alberta Hospital, said that's because the body is actually working against gravity in that position.

Bashir, who did the work while at University Hospital in Aberdeen, Scotland, said he and his colleagues found the most natural or neutral position was actually one in which the body was at a 135-degree angle — a posture that most closely approximated lying down.