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Abstract
Objectives. To identify painful stressor-induced surface electromyography [sEMG] responses in chronic low back pain [CLBP] patients and pain-free controls to experimental noxious stimulation, the cold pressor test [CPT] and investigate potential differences in pain report.
Methods. Fourteen CLBP patients and 12 age/gender matched controls underwent an identical sEMG recording protocol in six stages: baseline, hand in 15°C cool water, a recovery period, a CPT, a second recovery phase and a post-test evaluation. Surface electromyography was recorded at bilateral trapezius, and paraspinal sites at L5.
Results. Across all stages of the experiment there was no statistically significant difference in pain report. However, following the experiment patients reported significantly higher retrospective pain ratings than the controls using the Short Form-McGill Pain Questionnaire [SF-MPQ]. During baseline conditions, no differences in sEMG were noted between the groups. During the cool water condition, patients showed increased L5 sEMG in the left side compared to controls. Patients' elevated sEMG persisted after the hand was taken out of the cool water and increased further during the CPT. These group differences occurred for both sides and were most marked on the contralateral side to hand immersion. The increases on the ipsilateral side failed to reach significance. In contrast, the control subjects demonstrated increased sEMG activity in the trapezius muscles across the testing stages but this only reached significance for the right side.
Conclusions. These results suggest a preferential activation of the lumbar paraspinal muscle activation in CLBP patients during painful hand stimuli. In addition retrospective rating of experimental pain by CLBP patients, using the SF-MPQ may be unrepresentative of the experimental condition.