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Effect of Noxious Electrical Stimulation of the Peroneal Nerve on Stretch Reflex Activity of the Hamstring Muscle in Rats: Possible Implications of Neuronal Mechanisms in the Development of Tight Hamstrings in Lumbar Disc Herniation

Study Design. The effect of noxious electrical stimulation of the peroneal nerve on the stretch reflex electromyogram activity of the hamstring muscle (semitendinous) was studied. Objective. To verify the following hypothetical mechanisms underlying tight hamstrings in lumbar disc herniation: stretch reflex muscle activity of hamstrings is increased by painful inputs from an injured spinal nerve root and the increased stretch reflex muscle activity is maintained by central sensitization. Summary of Background Data. It is reported that stretch reflex activity of the trunk muscles is induced by noxious stimulation of the sciatic nerve and maintained by central sensitization. Methods. In spinalized rats (transected spinal cord), the peroneal nerve was stimulated electrically as a conditioning stimulus. Stretch reflex electromyogram activity of the semitendinous muscle was recorded before and after the conditioning stimulus. Results. Even after electrical stimulation was terminated, an increased stretch reflex activity of the hamstring muscle was observed. Conclusions. It is likely that a central sensitization mechanism at the spinal cord level was involved in the increased reflex activity. Central sensitization may play a part in the neuronal mechanisms of tight hamstrings in lumbar disc herniation.