Journal article
Fatigue modulates synchronous but not asynchronous soleus activation during stimulation of paralyzed muscle
Clinical neurophysiology, Vol.124(9), pp.1853-1860
09/2013
DOI: 10.1016/j.clinph.2013.03.027
PMCID: PMC3735624
PMID: 23673062
Abstract
•The soleus muscle H-reflex is larger after fatigue induced by supra-maximal repetitive stimulation.•“Asynchronous” EMG bursts, consistent with fluctuations in muscle force, were not prevalent during supra-maximal stimulation.•Supra-maximal stimulation, administered at physiologic frequencies (e.g. 15Hz), is a useful strategy to administer fixed levels of physiologic stress (force) to paralyzed tissues.
Electrical stimulation over a motor nerve yields muscle force via a combination of direct and reflex-mediated activation. We determined the influence of fatigue on reflex-mediated responses induced during supra-maximal electrical stimulation in humans with complete paralysis.
We analyzed soleus electromyographic (EMG) activity during repetitive stimulation (15Hz, 125 contractions) in 22 individuals with complete paralysis. The bout of stimulation caused significant soleus muscle fatigue (53.1% torque decline).
Before fatigue, EMG at all latencies after the M-wave was less than 1% of the maximal M-wave amplitude (% MaxM). After fatigue there was a fourfold (p<0.05) increase in EMG at the H-reflex latency; however, the overall magnitude remained low (<2% change in % MaxM). There was no increase in “asynchronous” EMG ∼ 1 s after the stimulus train.
Fatigue enhanced the activation to the paralyzed soleus muscle, but primarily at the H-reflex latency. The overall influence of this reflex modulation was small. Soleus EMG was not elevated during fatigue at latencies consistent with asynchronous activation.
These findings support synchronous reflex responses increase while random asynchronous reflex activation does not change during repetitive supra-maximal stimulation, offering a clinical strategy to consistently dose stress to paralyzed tissues.
Details
- Title: Subtitle
- Fatigue modulates synchronous but not asynchronous soleus activation during stimulation of paralyzed muscle
- Creators
- Richard K ShieldsShauna Dudley-Javoroski
- Resource Type
- Journal article
- Publication Details
- Clinical neurophysiology, Vol.124(9), pp.1853-1860
- DOI
- 10.1016/j.clinph.2013.03.027
- PMID
- 23673062
- PMCID
- PMC3735624
- NLM abbreviation
- Clin Neurophysiol
- ISSN
- 1388-2457
- eISSN
- 1872-8952
- Publisher
- Elsevier BV
- Language
- English
- Date published
- 09/2013
- Academic Unit
- Orthopedics and Rehabilitation; Physical Therapy and Rehabilitation Science
- Record Identifier
- 9984046907902771
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