"My back feels so stiff!" We often hear our friends say.

Well, that doesn't mean your friend's back is actually stiff, according to a new study.

"A conscious experience of feeling stiff does not reflect true biomechanical back stiffness," explained the senior author. "When we use the same word, stiffness, to describe a feeling and how we measure actual stiffness, we assume these words are describing the same thing. But that is not always the case."

In the study, the team asked participants how stiff their backs felt to them. After that, using a customized device, they measured just how stiff the back actually was.

"There was no relation between biomechanical stiffness and the reported feeling of stiffness," senior author said. "What people describe as stiffness is something different than the measurement of stiffness."

The lead author said that the feeling of stiffness may be a protective construct that is created by our nervous system.

"It's our body's way of protecting ourselves, possibly from strain, further injury or more pain," the lead author said.

With lower back pain being the leading cause of disability worldwide affecting approximately 632 million people, it is important to examine mechanisms associated with lower back pain and its symptoms, including stiffness.

"Words are important. The words patients use to describe a problem in the clinic may not be the same thing we as clinicians measure in the clinic," said the senior author. "We need to find out what it means exactly when someone says they have a stiff back. We now know it might not mean that their back is mechanically stiff.

It could mean they feel their movements are slower and more painful."

https://www.ualberta.ca/rehabilitation/news/2017/september/feeling-of-stiffness-may-mean-something-else-is-going-on-in-the-back/

https://www.nature.com/articles/s41598-017-09429-1