Reflexes Evoked in Various Human Muscles During Voluntary Activity

Abstract

Although the H reflex is theoretically recordable from all muscles, in practice it is consistently obtained only by recording from the triceps surae while stimulating the tibial nerve at the knee. It is known that voluntary muscle contraction makes it possible to evoke the H reflex from those muscles in which the reflex is normally unelicitable at rest, because the excitability of the corresponding motoneurones is increased by descending volitional impulses. In contrast to the H reflex, the T reflex, which is the monosynaptic spinal reflex elicited by a mechanical tap to the tendon and is equivalent in many respects to the H reflex, has not been sufficiently investigated in voluntarily contracting human muscles. In the present study, with a tendon tap during effort, the authors could consistently obtain the reflex responses from the tibialis anterior muscle (TA muscle), the abductor pollicis brevis muscle (APB muscle), and the paraspinal muscles. In addition to mechanical elicitation, electrical nerve stimulation was also employed to induce the responses in the TA and the APB muscles, allowing the further assessment of the nature of the responses by comparing the mechanically elicited reflex responses with the electrically elicited ones.