Downslope walking and the H-reflex pathway: dose-response effect and generalizability Público

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

About this Honors Thesis

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• Permission granted by the author to include this thesis or dissertation in this repository. All rights reserved by the author. Please contact the author for information regarding the reproduction and use of this thesis or dissertation.

School	Emory College
Department	Neuroscience and Behavioral Biology
Degree	BS
Submission	Honors Thesis
Language	English
Research Field	Biology, Physiology Biology, Neuroscience Health Sciences, Rehabilitation and Therapy
Palabra Clave	dose-response homosynaptic depression spinal excitability recurrent inhibition treadmill
Committee Chair / Thesis Advisor	Sabatier, Manning, Emory University
Committee Members	Hochman, Shawn, Emory University Crutcher, Michael D, Emory University

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