H reflexes in close muscles: cross-talk or genuine responses?

At rest, common peroneal nerve stimulation induced weak H responses in the peroneus longus (PL) and/or in the tibialis anterior (TA) muscles in half the subjects. The genuine H response of each muscle had to be proved since cross-talk could be suspected. PL and TA H responses were identified since (i) the reflex was often observed in only one muscle; (ii) H and M recruitment curves of each muscle were not systematically correlated; (iii) weak voluntary contractions induced opposite reflex changes in the antagonist PL and TA; (iv) direct stimulation of one of the muscles did not induce any cross-talk in the other provided that the EMG was of low voltage. It is concluded that H reflexes of close muscles can be studied independently.