The effect of ankle joint position and effort on quadriceps reflex sensitivity

Objective: To investigate a possible ankle-knee synergy, experiments with n ormal subjects were performed to compare changes of the quadriceps motor po ol excitability due to ankle position and effort. Methods: Vastus medialis H reflex amplitude was examined during ankle isome tric contractions conditioned by different ankle positions (dorsiflexion, n eutral, and plantarflexion) with or without voluntary effort (either in the dorsiflexion or plantarflexion direction). Repeated measures ANOVAs were p erformed on the mean and standard deviation of the H peak-to-peak amplitude . Results: Mean vastus medialis H reflex amplitudes were significantly differ ent among the trials of different ankle efforts (P < 0.05), and significant ly increased during plantarflexion efforts. In contrast, mean vastus medial is H reflex amplitude did not vary with respect to changes of ankle positio n (P > 0.05). Conclusions: The data suggest that (1) the position of the ankle joint did not significantly modify the excitability of the neuromotor pool of the VM muscle, in either static or active cases, and (2) the effort effect from th e ankle joint on the VM neuromotor pool is most significant during ankle pl antarflexion effort. Possible mechanisms are central motor irradiation and peripheral force-dependent pathways from the ankle joint that influence the VM neuromotor pool. (C) 2000 Elsevier Science Ireland Ltd. All rights rese rved.