Interlimb reflexes of the lower limb elicited by femoral nerve stimulation in able-bodied persons.

Sensory feedback arising from muscles in the lower limb makes an important contribution to the activation of muscles on the opposite side. To date little is known about this interlimb communication for muscles of the upper leg. Here, we quantify interlimb reflexes of the quadriceps muscles elicited by femoral nerve stimulation. The reflex response of 10 able-bodied participants was analyzed at eight stimulation intensities [0.7× motor threshold (MT)-100% maximal M-wave (M-max)], during standing and sitting. Electromyographic (EMG) signals of the contralateral vastus lateralis (cVL), rectus femoris (cRF), biceps femoris (cBF), and soleus (cSOL) muscle were analyzed. Significant inhibitory long-latency responses were observed at stimulation intensities higher than 0.7 × MT, for the cVL and cRF. Onset latencies ranged from 67 ± 12 ms to 70 ± 13 ms during standing and from 61 ± 14 ms to 67 ± 15 ms during sitting. The strongest depression (-32.39% compared with baseline EMG activity) was observed for the cRF during standing at 50% M-max. The cBF showed excitatory long-latency responses during standing (strongest at 100% M-max with +52.36%) and inhibitory once during sitting, and small excitatory short-latency responses during standing. The cSOL showed inhibitory long-latency responses (-18.15% at 25% M-max) during standing. In conclusion, the results show that femoral nerve stimulation elicits consistent contralateral reflex responses in the quadriceps muscles. The occurrence at all intensities suggests that group Ia, Ib, and II afferents are involved in the pathways.NEW & NOTEWORTHY This study introduced a method to consistently elicit contralateral reflex responses in the quadriceps muscles through femoral nerve stimulation. Responses of the contralateral vastus lateralis (cVL), contralateral rectus femoris (cRF), and contralateral soleus (cSOL) occurred only in the long-latency range, whereas the contralateral biceps femoris (cBF) showed small short-latency and long-latency activity.