Feelings of back stiffness don’t necessarily correspond with what’s going on in the body, according to a study published in Scientific Reports.
In fact, 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,” explained Tasha Stanton, lead author and senior research fellow of pain neuroscience at the University of South Australia.
In the study, the researchers asked participants how stiff their backs felt to them. After that, using a customised device, they measured just how stiff the back actually was.
Over three experiments, they found that feeling stiff does not relate to objective spinal measures of stiffness and objective back stiffness does not differ between those who report feeling stiff and those who do not.
Instead, those who report feeling stiff exhibit self-protective responses: they significantly overestimate force applied to their spine, yet are better at detecting changes in this force than those who do not report feeling stiff.
“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,” said Greg Kawchuk, professor and back and spine expert in the University of Alberta’s Department of Physical Therapy.
With lower back pain affecting approximately 632 million people around the world, the researchers said it’s 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,” Kawchuk said. “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.”