Effect of manual acupuncture and transcutaneous electrical nerve stimulation on the H-reflex

Several studies find that manual acupuncture and transcutaneous electrical nerve stimulation (TENS) are via different mechanisms and generate different effect on the central nervous system, therefore, the aim of the present study was to compare the effect of manual acupuncture (MA) and TENS on the spinal cord using H-reflex recordings. A total of 13 healthy adult volunteers were studied. The electrical stimuli were delivered to the posterior tibial nerve transcutaneously at the left popliteal fossa to evoke the soleus H-reflex. MA, 2Hz TENS, 100 Hz TENS, respectively, was applied to the surface of the right first dorsal interosseous muscle exactly at the Hegu acupoint (LI.4). Four assessments were performed randomly, separated by an interval of at least three days in all the subjects as follows: 1) Control assessment: a pair of electrodes placed on the surface of the right Hegu acupoint (LI.4), but no electrical stimulation was delivered throughout the test; 2) MA assessment: MA was done at the right Hegu acupoint (LI.4) for 15 minutes; 3) TENS assessment at 2Hz: electrical stimulation (40 mA in intensity) at 2Hz was applied to the surface of the right Hegu acupoint (LI.4) for 15 minutes; 4) TENS assessment at 100 Hz: electrical stimulation (20 mA in intensity) at 100 Hz was applied to the surface of the right Hegu acupoint (LI.4) for 15 minutes. Each assessment was divided into three periods as follows: 1) Baseline period: H-reflexes recorded prior to MA or TENS; 2) TENS period: six H-reflex recordings after MA or TENS for a duration of 4-5 min, 9-10 min and 14-15 min, respectively; 3) Post TENS period: H-reflex recordings of 6 after TENS period 4-5 min and 9-10 min, respectively. Our results indicate that both 2Hz TENS and 100 Hz TENS increased the amplitude of the H-reflex, and that these increases may be retained longer with 100 Hz TENS than with 2 Hz TENS, whereas MA could not increase the amplitude of the H-reflex. MA, TENS at 2 Hz or 100 Hz didn't change the latencies of the H-reflexes. We conclude that both 2Hz and 100 Hz TENS increased the amplitude of the H-reflex, suggesting that TENS enhances the excitability of the motoneuron pool in the spinal cord, and 100 Hz TENS has a greater effect than 2Hz TENS, whereas MA was not similar effect to TENS on spinal cord.