The Recovery Curve of Soleus and Gastrocnemius H-Reflex After Applying Tripolar Electrical Stimulation on the Anesthetized Skin of Vertebral Column: An Emphasis on the Early and Secondary Facilitation Phases

Computer modeling studies have shown that depolarization of the posterior and anterior root fibers can be achieved by surface tripolar electrical stimulation. This study investigated the soleus and gastrocnemius H-reflex recovery curve after applying tripolar electrical stimulation on the anesthetized skin of vertebral column. We emphasized on the early and secondary facilitation phases of the H-reflex recovery curve.
Material and A total of 15 healthy nonathletic female volunteers (mean±SD age: 27.20±3.17 years) were enrolled in this study. H-reflex recovery curves of the soleus and gastrocnemius muscles were recorded before skin anesthesia and then 15 minutes after it (with lidocaine 10%) and finally after application of Transcutaneous Electrical Nerve Stimulator (TENS) or placebo TENS (TENS on/off). Tripolar TENS with pulse width of 300 µs, frequency of 80 Hz and intensity of 1.5 times of the sensory threshold was used for 15 minutes at the level of T11. To record the H-reflex recovery curve, 34 paired stimuli were used with the intensity of 30% H max and interstimulus intervals between 1 and 202 ms. After drawing the H-reflex recovery curve, amplitude, slope, area under the curve, and threshold of the early and secondary facilitation phases were calculated.
After application of topical lidocaine, the sensory threshold of the skin vertebral column increased significantly. Fifteen minutes after applying local anesthesia, peak amplitude, slope, and area under the curve of the early facilitation phase significantly decreased in gastrocnemius and soleus muscles. After tripolar TENS application on the anesthetized skin of vertebral column, the slope of the early facilitation phase decreased significantly in the soleus (P=0.047). Also, area under the curve of the secondary facilitation phase significantly increased in both muscles.
These findings suggest the excitatory effect of skin anesthesia on the motoneurons activities. Changing the H-reflex recovery curve after application of tripolar TENS on the anesthetized skin may confirm deep penetration of this type of electrical stimulation.