Crying Wolf about Low Back Pain
Accurately measuring physical impairment is easier said than done. So far, most of the strategies identified by researchers don't work. One of the factors that makes such measurement difficult is that patients sometimes exaggerate their symptoms when they bend and twist in the doctor's office. Patients may exaggerate their impairments on purpose--to get treatment, medication, or disability status. But many patients exaggerate their symptoms without even knowing it. They may be afraid of causing themselves pain, or they may simply be nervous about being in the doctor's office.  

These authors used exaggeration to gauge the usefulness of one method of measuring low back impairment. They tested two groups of 100 people each. One group had low back problems, and the other group didn't. Both groups underwent a physical examination while wearing a device to monitor their body movements. The participants bent forward, bent side to side, and twisted their trunk back and forth. They did their best with each motion on the first try. The second time they were told to move as if their back was more painful than it actually was. 

The results showed that the monitor was fairly accurate in determining which motions were real and which ones were exaggerated. This suggests that the device might be a useful way to more accurately measure low back impairment.

It also supports the theory that we tend to move our bodies in set patterns--unless, of course, we're faking it. The monitor showed erratic patterns of movement when people tried to exaggerate their motion. They simply couldn't fake it the same way twice.
William S. Marras, PhD, et al. Impairment Magnification During Dynamic Trunk Motions. In Spine. March 1, 2000. Vol. 25. No. 5. Pp. 587-595.