Downslope walking and the H-reflex pathway: dose-response effect and generalizability Open Access
Arnold, Elizabeth Ann (2016)
Abstract
The purpose of this study was to determine whether downslope treadmill walking reduces spinal excitability in a dose-dependent manner. Soleus (Sol) and tibialis anterior (TA) H-reflexes were measured in twelve neurologically intact adults on four or five days. Measurements were taken before and after four downslope walking (DSW) doses (10 minutes at -15%, 20 minutes at -15%, 10 minutes at -25%, 20 minutes at -25%) at 2.5 mph, and eight participants also completed level walking (LW) for 20 minutes. To obtain the Sol and TA H-reflex and M-wave recruitment curves, the tibial nerve (Sol) and common peroneal nerve (TA) were electrically stimulated with a range of stimulus intensities while participants maintained background activity at 20% of maximum Sol and TA activity, respectively. The H-reflex was expressed as the ratio of Hmax to Mmax. Recurrent inhibition was measured as the percent difference between the unconditioned H-reflex and conditioned H-reflex. Heart rate (HR) and ratings of perceived exertion (RPE) were measured during walking. DSW for 20 minutes at -15%, 10 minutes at -25%, and 20 minutes at -25% caused greater Sol Hmax/Mmax depression than LW (30 ± 21%, 34 ± 23%, 36 ± 22% vs. 15 ± 15%, P ≤.02), and DSW for 20 minutes at -25% caused greater Hmax/Mmax depression than 10 minutes at -15% (36 ± 22% vs. 18 ± 23%, P ≤ .01). There was no effect of LW or DSW on TA H-reflexes or recurrent inhibition. HR and RPE were highest during DSW at the -25% slope. In conclusion, DSW causes dose-dependent depression of Sol H-reflexes, but only when comparing the smallest and largest DSW doses, and these effects are not generalizable to the TA.
Table of Contents
List of Figures and Tables. i
1 Introduction. 1
1.1 Spasticity in Neurologically Damaged Individuals. 1
1.2 The Stretch Reflex and the Hoffman (H) Reflex. 3
1.3 H-Reflex Modulation. 7
1.4 Downslope Walking (DSW) and H-Reflex Depression. 10
1.5 Hypotheses. 14
2 Methods. 14
2.1 Participants. 14
2.2 Design. 15
2.3 Walking Procedure. 16
2.4 Soleus H-reflexes. 16
2.5 Tibialis Anterior H-reflexes. 17
2.6 Recurrent Inhibition. 18
2.7 Statistical Analysis. 18
3 Results. 19
3.1 Heart Rate, Perceived Exertion, and Soreness. 19
3.2 Soleus and TA Hmax/Mmax Ratios. 20
3.3 Recurrent Inhibition. 24
4 Discussion. 26
4.1 Effects of Slope and Duration of Downslope Walking on H-reflexes. 27
4.2 Recurrent Inhibition. 30
4.3 Clinical Relevance of Downslope Walking. 31
5 References. 33
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