The effects of vertebral column tripolar electrical stimulation with various intensities on soleus and gastrocnemius H-reflex and Mh wave recruitment curve

Introduction: Computer modeling of tripolar electrical stimulation has shown that this kind of electrode placement can stimulate deeper in tissues. Application of this kind of stimulation method on vertebral column in order to stimulate deep tissues in this region can be clinically beneficial. Methods: To assess the effect of penetration depth of the surface Tripolar electrical stimulation, Tripolar TENS was applied with different intensities (with 1.25 and 1.5 sensory thresholds (ST)) on the vertebral column of 20 healthy subjects. The cathode of TENS was laid on the T11 vertebra and the anodes were put 3 cm apart from the cathode longitudinally, in anode-cathode-anode arrangement. The recruitment curve of soleus and gastrocnemius H-reflex and M wave were recorded before, immediately after and 10 min after TENS. Experiments were performed in 4 separate sessions. One of the experiments was control session, during which the TENS apparatus was off during the session. In each of the test sessions, TENS was applied with one of the mentioned intensities. Results: The results showed that 1.5 ST TENS had a complex facilitatory-inhibitory effect on the recruitment curve of soleus H-reflex. With this intensity, slow motoneurons were inhibited and fast motoneurons were facilitated. Also, the positive slope of the curve was increased and the intensity needed to evoke Hmax was decreased. Furthermore, the amplitude of Hmax and the threshold of the curve were slightly decreased. Gastrocnemius was facilitated after 1.5 ST TENS and the threshold of the H-reflex curve and needed intensity to evoke Hmax were decreased, while peak to peak amplitude of Hmax was increased. After 1.25 ST TENS, soleus was facilitated and gastrocnemius had inhibitory trend. Conclusion: Tripolar TENS with 1.5 ST intensity stimulates the tissue more deeply and therefore causes different outcomes from tripolar TENS with lower STs.