Influence of body position on crossed-spinal excitability in high-risk fallers

Abstract

The purpose of this study was to examine the role body position plays on crossed-spinal excitability in high-risk fallers. Specifically, we examined the time-course modulation of the soleus H-reflex following a conditioning stimulation from the contralateral common peroneal nerve in high-risk fallers. Four high-risk fallers (72.65 ± 5.22 years) volunteered to participate in this study. Two body positions were studied: supine and standing. A conditioning stimulus was given to the contralateral common peroneal nerve of the left leg followed by a test stimulus at varying interstimulus intervals 25-300ms) to the ipsilateral tibial nerve of the right leg to elicit a soleus H-reflex. Surface EMG electrodes from were used to record EMG activity of the left tibialis anterior and right soleus muscles. The peak-to-peak amplitude of the soleus H-reflex was recorded ten times at each ISI and control (unconditioned) stimulations to the soleus muscle. The highest and lowest values at each ISI were removed and the remaining 8 peak-to-peak amplitudes were averaged. For all calculations, the alpha level was set at the .05 level. A 2 x 6 ANOVA (body position by interval) revealed no significance interaction F(5, 15) = 0.23, p= 0.93. Similarly there was no significant main effect for body position F(1, 15) = 0.178, p= 0.702 or interval F(5, 15) = 01.29, p= 0.319. A post hoc power analysis was conducted using G-Power. This analysis indicated that approximately 8-14 subjects would be needed to detect significant differences in reflex modulation in high-risk fallers at the 0.05 level of significance.