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Increased spinal reflex excitability is associated with enhanced central activation during voluntary lengthening contractions in human spinal cord injury.

Abstract：

:This study of chronic incomplete spinal cord injury (SCI) subjects investigated patterns of central motor drive (i.e., central activation) of the plantar flexors using interpolated twitches, and modulation of soleus H-reflexes during lengthening, isometric, and shortening muscle actions. In a recent study of the knee extensors, SCI subjects demonstrated greater central activation ratio (CAR) values during lengthening (i.e., eccentric) maximal voluntary contractions (MVCs), compared with during isometric or shortening (i.e., concentric) MVCs. In contrast, healthy controls demonstrated lower lengthening CAR values compared with their isometric and shortening CARs. For the present investigation, we hypothesized SCI subjects would again produce their highest CAR values during lengthening MVCs, and that these increases in central activation were partially attributable to greater efficacy of Ia-α motoneuron transmission during muscle lengthening following SCI. Results show SCI subjects produced higher CAR values during lengthening vs. isometric or shortening MVCs (all P < 0.001). H-reflex testing revealed normalized H-reflexes (maximal SOL H-reflex-to-maximal M-wave ratios) were greater for SCI than controls during passive (P = 0.023) and active (i.e., 75% MVC; P = 0.017) lengthening, suggesting facilitation of Ia transmission post-SCI. Additionally, measures of spinal reflex excitability (passive lengthening maximal SOL H-reflex-to-maximal M-wave ratio) in SCI were positively correlated with soleus electromyographic activity and CAR values during lengthening MVCs (both P < 0.05). The present study presents evidence that patterns of dynamic muscle activation are altered following SCI, and that greater central activation during lengthening contractions is partly due to enhanced efficacy of Ia-α motoneuron transmission.

journal_name

J Neurophysiol

journal_title

Journal of neurophysiology

authors

Kim HE,Corcos DM,Hornby TG

doi

10.1152/jn.01074.2014

subject

Has Abstract

pub_date

2015-07-01 00:00:00

pages

427-39

issue

eissn

0022-3077

issn

1522-1598

pii

jn.01074.2014

journal_volume

114

pub_type

杂志文章

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Increased spinal reflex excitability is associated with enhanced central activation during voluntary lengthening contractions in human spinal cord injury.