Longer Duration of Downslope Treadmill Walking Induces Depression of H-Reflexes Measured during Standing and Walking

Objectives: The Hoffman-reflex (H-reflex) is an electrophysiological technique used to evaluate the excitability of the monosynaptic spinal reflex arc. In individuals with upper motor neuron lesions who show elevated spinal excitability, a depression of spinal excitability may indicate adaptive spinal plasticity. Downslope walking (DSW), an exercise intervention comprising repetitive eccentric muscle activity, has been shown to induce depression of soleus H-reflex amplitudes while seated, however, the dose-response time-course of H-reflex modulation during DSW has not been characterized. The objectives of this study were twofold: (1) to evaluate DSW-induced soleus H-reflex depression in the standing posture and during walking, and (2) to investigate the effect of walking duration (20 minutes and 40 minutes) of DSW (-15% decline) on soleus H-reflexes, (with level walking (LW) as a control intervention). Methods: Soleus H-reflexes were collected Pre, Post-20 minutes, and Post-40 minutes of walking in the standing position; and H-reflexes were also measured at 4 different time points during the terminal stance phase of walking. Results: Our results showed that soleus H-reflexes evaluated in standing showed a greater % depression after DSW compared to LW, with a statistical trend for greater depression with longer durations (40-minutes). H-reflexes measured during walking showed greater depression after 40 minutes of walking compared to 20- or 30-minutes for both DSW and LW. Conclusions: Longer duration treadmill walking (40-minutes) may induce a greater acute depressive effect on soleus H-reflex excitability compared to shorter durations (20-minutes) of treadmill walking. Future work will investigate the potential for DSW as a gait training intervention in people with upper motor neuron lesions such as multiple sclerosis and stroke.