Is Reciprocal Facilitation a Myth in Upper Motor Neuron Lesions?

Study Design: Clinical trial Objective: To investigate whether reciprocal facilitation is a pseudo-reflex response resulting from crosstalk or cross-stimulation using the MMU EMG technique. Setting: Istanbul Physical Therapy Rehabilitation Training and Research Hospital, Istanbul, Turkiye Methods: Five individuals with chronic incomplete spinal cord lesions (SCL) and five able-bodied volunteers participated in the study. To trigger the reciprocal facilitation response in the tibialis anterior muscle, the Soleus T-reflex was induced by tapping the Achilles tendon, while the Soleus H-reflex was elicited by stimulating the tibialis nerve. Reflex responses were simultaneously recorded from the right soleus and right tibialis anterior muscles using both surface electromyography (sEMG) and multi-motor unit (MMU) EMG. Results: It was noted that the EMG responses initially interpreted as reciprocal facilitation in both able-bodied individuals and those with SCL were actually due to cross-stimulation. Specifically, it was found that when the tibial nerve was stimulated with an electrical current to evoke the soleus H-reflex, simultaneous stimulation of the peroneal nerve occurred, resulting in the occurrence of both tibialis anterior H-reflex and M wave (cross-electrical stimulation). Additionally, striking the Achilles tendon with a reflex hammer to elicit the soleus T-reflex resulted in mechanical stimulation spreading to both the soleus and tibialis anterior muscle bellies, activating the muscle spindles and eliciting both soleus and tibialis anterior T-reflex responses (cross-mechanical stimulation). Conclusions: No evidence supporting reciprocal facilitation was found. Further research utilizing H-reflex and T-reflex tests, resolving the cross-stimulation issue, is needed to establish its existence conclusively.