SURFACE ELECTROMYOGRAPHY IN THE IDENTIFICATION OF CHRONIC LOW-BACK-PAIN PATIENTS - THE DEVELOPMENT OF THE FLEXION RELAXATION RATIO

Objective. To develop a reliable and repeatable way to monitor changes in the flexion relaxation phenomenon of the lumbar paraspinal muscles during forward flexion by the development of a flexion relaxation rat io and observation of the sEMG activity in standing and during forward flexion in patients with chronic low back pain (CLBP) and healthy con trols. Design. Two experiments were conducted, the first to assess the test-retest reliability of the measure in a group of CLBP (n = 11) pa tients; the second compared the results between a group of normal heal thy controls (n = 20) and a group of CLBP patients (n = 70). Results. Repeated measurements over 4 weeks demonstrated between session reliab ility of between 0.81 and 0.98 for the dynamic activity. The levels of sEMG activity in the fully flexed position was significantly greater in the fully flexed position in the CLBP group than the controls. The flexion relaxation ratio (FRR), a comparison of the maximal sEMG activ ity during 1 s of forward flexion with activity in full flexion, demon strated significantly lower values in the CLBP than the control group. The combined discriminant validity for the FRR for all four sites res ulted in 93% sensitivity and 75% specificity. Conclusion. The FRR clea rly discriminated the patients from the healthy controls. These result s indicate that dynamic sEMG activity of the paraspinal muscles can be reliably measured and is useful in differentiating CLBP patients from normal controls. Relevance Analysis of the pattern of different level s of muscle activity during a forward flexion can be used in CLBP wher e normalization of the sEMG signal to the maximum voluntary contractio n may be difficult. The FRR may be used in the assessment of change in the flexion relaxation phenomenon following treatment interventions. (C) 1997 Elsevier Science Ltd.