Walking duration and slope steepness determine the effect of downslope walking on the soleus H-reflex pathway

Abstract

The purpose of this study was to determine if the effect of downslope walking (DSW) on spinal excitability depends on walking duration and slope steepness, and if findings from the soleus (Sol) generalize to the tibialis anterior (TA). Sol and TA Hmax and Mmax were measured before and after four DSW doses (time/slope, min/%) on separate days (10/-15, 20/-15, 10/-25, 20/-25, n=14), and one 20-min bout of level walking (LW, n=12), always at 2.5 mph. Heart rate (HR) and ratings of perceived exertion (RPE) were measured during walking. DSW for all doses except 10/-15 caused greater Sol Hmax/Mmax depression than LW (p≤0.02), and 20/-25 caused greater Hmax/Mmax depression than 10/-15 (p≤0.01). TA H-reflex curves were substantially smaller than Sol H-reflex curves, and this study was unable to detect an effect of LW or DSW on TA Hmax/Mmax. Although HR and RPE were significantly higher during DSW at -25% than at -15% slope, group HR and RPE nevertheless peaked at relatively low values of 101.4±14.2 bpm and 12.6±2.3, respectively. In conclusion, DSW duration and slope steepness interact to determine the magnitude of Sol H-reflex depression, but these effects do not generalize to the TA.

Keywords: Locomotion; Spinal excitability; Spinal plasticity; Treadmill.