OBJECTIVE: To investigate to what extent a single 60-minute session of transcutaneous electrical nerve stimulation (TENS) would modify chronic clinical pain, acute experimental pain, and the flexion reflex evoked in chronic low back pain patients. STUDY DESIGN: Thirty young subjects with chronic low back pain were randomly allocated to two groups, receiving either TENS or placebo stimulation to the lumbosacral region for 60 minutes. The flexion reflex was elicited by an electrical stimulation applied to the subject's right sole and recorded electromyographically from the biceps femoris and the tibialis anterior muscles. MAIN OUTCOME MEASURES: Subjective sensation of low back pain and the electrically induced pain were measured by two separate visual analog scales, termed VAS(LBP) and VAS(FR), respectively. Data obtained before, during, and 60 minutes after TENS and placebo stimulations were analyzed using repeated measures ANOVA. RESULTS: The VAS(LBP) score was significantly reduced to 63.1% of the prestimulation value after TENS (p < 0.001), but the reduction was negligible after placebo stimulation (to 96.7%, p = 0.786). In contrast, no significant change was found in the VASFR score (p = 0.666) and the flexion reflex area (p = 0.062) during and after stimulation within each group and between the two groups (p = 0.133 for VASFR and p = 0.215 for flexion reflex area). CONCLUSIONS: The same TENS protocol had different degrees of antinociceptive influence on chronic and acute pain in chronic low back pain patients.

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