Heteronymous reflex responses in a hand muscle when maintaining constant finger force or position at different contraction intensities

ObjectiveThis study compared heteronymous reflex responses evoked in the first dorsal interosseous muscle by electrical and mechanical stimuli during force and position tasks performed at different target torques.MethodsTwenty-two healthy human participants contracted the first dorsal interosseus muscle either to produce a constant force against a rigid restraint (force task) or to maintain a constant position of the index finger (position task) against a constant load of 20, 40, and 60% of maximum.ResultsThe amplitude of the short-latency reflex evoked by electrical stimulation of the median nerve was significantly greater when maintaining finger position, whereas no difference was present for the long-latency responses. In contrast, the reflex responses (short- and long-latency) did not differ between tasks when elicited by tendon-taps.ConclusionsTask difference in reflex responsiveness depended more on the type of stimulus applied than the reflex pathway and was consistent across three voluntary contraction forces.SignificanceThe results suggest that afferent input from homonymous and heteronymous pathways is modulated similarly at the spinal level during such tasks, and implies the significance of presynaptic inhibition during motor performance.