Do pain expectancies cause pain in chronic low back patients? A clinical investigation.

The present study investigated whether pain expectancies cause pain in chronic low back patients. Back patients (N = 29) were requested to perform four exercise bouts (two with each leg), each consisting of flexing and extending the knee three times at maximal force (Cybex 350 System). During each exercise bout the baseline pain, the expected pain and experienced pain were recorded. Patients also reported their experienced fear of further injury to the back. Furthermore, the peak force of both knee flexors and extensors was assessed. Although patients did expect a back pain increase during the first exercise bout with each leg, no evidence was found for the thesis that pain expectancies generate increases in subjective pain experiences. Instead, the reported pain expectancy was readily corrected during the next exercise bout, whereas the experienced pain remained unchanged. Furthermore, a high pain expectancy co-occurred with (1) a marginally significant fear of (re)injury, and (2) a significant lower peak torque of the knee flexors. These results are consistent with conditioning models which state that pain expectations are associated with a fear response and an urge to avoid the pain.