The purpose of this study was to test the effect of arm swing on modulation of soleus H-reflexes amplitudes during walking. Fifteen subjects walked (1.07 m/s) on a treadmill in 4 arm swing conditions: 1-natural arm swing (control), 2-active restraint, 3-passive restraint, and 4-passive-assisted. Tibial nerve was electrically stimulated and soleus EMG was recorded. H-reflex amplitude was significantly greater during active than during passive restraint (p = .013). Remaining arm swing conditions were not significantly different. We detected a subtle effect of arm swing on soleus H-reflex amplitude. Descending regulation may serve as a gating mechanism to control the effect of arm movements on reflex pathways for leg muscles. This gating mechanism may be impaired postneural injury, potentially enhancing the modulation of peripheral sensory inputs on reflexes in leg muscles during walking. Future experiments to test additional conditions and evoking reflexes in more phases of walking are recommended.
Phadke and Behrman are with the Department of Physical Therapy, University of Florida, Gainesville, FL, USA and the Veterans Affairs Brain Rehabilitation Research Center, Gainesville. Thompson is with the Department of Neuroscience, University of Florida, Gainesville. Klimstra and Zehr are with the School of Exercise Science, Physical and Health Education, and Rehabilitation Neuroscience Laboratory, University of Victoria, Victoria, BC, Canada.