Neural mechanisms underlying the effect of transcutaneous electrical nerve stimulation in humans

The aim of the present study was to observe the effect of transcutaneous electrical nerve stimulation (TENS) and to determine which group of afferent nerve fibers plays a role in this effect. The subjects were 43 healthy humans. The subjects received placebo intervention, TENS to the common peroneal nerve or to the cutaneous branches of the peroneal nerve. All TENS interventions decreased the Hmax/Mmax ratio. All the TENS interventions but the TENS below the motor threshold to the common peroneal nerve increased the H-reflex latency. The effect of TENS on Ia-mediated presynaptic inhibition varied according to the stimulation. Both group Ia and group II cutaneous afferent nerve fibers from the peroneal nerve are considered to mediate the inhibitory effect on the soleus motoneuron pool. Group II cutaneous afferent nerve fibers are considered to play an important role in increasing soleus H-reflex latency.