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

Stéphane Baudry *, Kimberlee Jordan, Roger M. Enoka
Department of Integrative Physiology, University of Colorado, Boulder, CO 80309-0354, USA

Clinical Neurophysiology 120 (2009) 210–217
doi:10.1016/j.clinph.2008.10.013

Abstract:

Objective: This 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.

Methods: Twenty-two healthy human participants contracted the first dorsal interosseus muscle eitherto 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.

Results: The amplitude of the short-latency reflex evoked by electrical stimulation of the median nervewas significantly greater when maintaining finger position, whereas no difference was present for thelong-latency responses. In contrast, the reflex responses (short- and long-latency) did not differ betweentasks when elicited by tendon-taps.

Conclusions: Task difference in reflex responsiveness depended more on the type of stimulus applied than the reflex pathway and was consistent across three voluntary contraction forces.

Significance: The 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.