Soleus H-reflex Modulation During Stance Phase of Walking with Altered Arm Swing Patterns

Abstract

PURPOSE: Rhythmic arm swing assists in propulsion, balance, and posture while walking; whereas inhibition of arm swing during walking leads to abnormal leg movements, decreased forward propulsion, and decrease in walking speed. Apart from these biomechanical effects, the neural contribution of arm swing to walking is not well-understood. The aim of this study was to examine the effect of various arm swing patterns on soleus H-reflex excitability during the stance phase of walking. We hypothesized that restraining the rhythmic arm swing would lead to an increase in soleus H-reflex amplitude during stance. METHODS: Fifteen non-injured subjects walked over the treadmill at 1.2 m/s speed with four different pseudo-randomly ordered arm swing conditions: 1) Control condition: natural reciprocal arm swing; Altered arm swing patterns - 2) active restraint of arm swing (arms by the side; voluntarily inhibiting arm swing); 3) passive restraint of arm swing (arms lightly strapped to the trunk); and 4) passive-assisted arm swing (subjects asked to relax arms and a trainer provided rhythmic reciprocal arm swing). In the mid-stance phase of walking, the tibial nerve was electrically stimulated in the popliteal fossa and surface EMG was recorded from the soleus muscle. RESULTS: H-reflex amplitudes in the altered arm swing conditions were not significantly different from the (control) natural reciprocal arm swing condition (p>0.05). However, H-reflex amplitudes in the active restraint condition was significantly greater than the passive restraint condition (p<0.05). CONCLUSION: Walking H-reflexes are centrally modulated to cope with the task demands. Our results suggest that soleus H-reflex depression in the mid-stance phase of walking at normal speed does not change significantly with the three arm swing alterations we used in this study. To further our understanding of neurological contribution of arm swing during locomotion, future studies need to be conducted during faster walking speeds/running and in subjects with neurological injury examined across all phases of walking.