Anal sphincter fatigue: Is the mechanism peripheral or central?

Schabrun, Siobhan M., Stafford, Ryan E. and Hodges, Paul W. (2011) Anal sphincter fatigue: Is the mechanism peripheral or central?. Neurourology and Urodynamics, 30 8: 1550-1556. doi:10.1002/nau.21162


Author Schabrun, Siobhan M.
Stafford, Ryan E.
Hodges, Paul W.
Title Anal sphincter fatigue: Is the mechanism peripheral or central?
Journal name Neurourology and Urodynamics   Check publisher's open access policy
ISSN 0733-2467
1520-6777
Publication date 2011-01-01
Year available 2011
Sub-type Article (original research)
DOI 10.1002/nau.21162
Open Access Status Not yet assessed
Volume 30
Issue 8
Start page 1550
End page 1556
Total pages 7
Place of publication Hoboken, NJ, United States
Publisher John Wiley & Sons
Language eng
Abstract Aims: Striated muscles of continence appear to exhibit marked fatigue during voluntary efforts. This is counterintuitive considering the high proportion of slow twitch muscle fibers. One explanation is that fatigue is due to central, rather than peripheral mechanisms. Here we examined the contribution of reduced voluntary activation (central fatigue) to the decline in anal sphincter (AS) and elbow flexor muscle force during voluntary contractions. Methods: Ten healthy subjects participated. Fatigue was induced using 10 maximal voluntary contractions sustained for 20 s. During each fatiguing contraction, transcranial magnetic stimulation (TMS) was delivered over the motor cortex at 5 s intervals. Central fatigue was assessed using the superimposed twitch force elicited by TMS. Peripheral fatigue was measured using brachial plexus (elbow flexors) or sacral plexus (AS) stimulation during contraction and at rest. Results: Ability to maximally activate AS (75.9%) was less than for the elbow flexors at baseline (91.6%). Voluntary activation declined in both muscles, but the decline was greater in AS (AS 28%; elbow flexors 12%). There was no change in the amplitude of the twitch evoked by peripheral nerve stimulation in either muscle. Conclusions: AS exhibits a greater decline in voluntary activation during fatiguing contractions than elbow flexor muscles. This is not accompanied by peripheral changes, which implies central mechanisms are responsible. Thus, we conclude that AS is susceptible to central fatigue during maximal voluntary activations. We propose this maybe a protective mechanism to conserve contractile potential of the anal sphincter for function. Neurourol. Urodynam. 30:1550-1556, 2011. (C) 2011 Wiley Periodicals, Inc.
Formatted abstract
Aims: Striated muscles of continence appear to exhibit marked fatigue during voluntary efforts. This is counterintuitive considering the high proportion of slow twitch muscle fibers. One explanation is that fatigue is due to central, rather than peripheral mechanisms. Here we examined the contribution of reduced voluntary activation (central fatigue) to the decline in anal sphincter (AS) and elbow flexor muscle force during voluntary contractions.
Methods: Ten healthy subjects participated. Fatigue was induced using 10 maximal voluntary contractions sustained for 20 s. During each fatiguing contraction, transcranial magnetic stimulation (TMS) was delivered over the motor cortex at 5 s intervals. Central fatigue was assessed using the superimposed twitch force elicited by TMS. Peripheral fatigue was measured using brachial plexus (elbow flexors) or sacral plexus (AS) stimulation during contraction and at rest.
Results: Ability to maximally activate AS (75.9%) was less than for the elbow flexors at baseline (91.6%). Voluntary activation declined in both muscles, but the decline was greater in AS (AS 28%; elbow flexors 12%). There was no change in the amplitude of the twitch evoked by peripheral nerve stimulation in either muscle.
Conclusions: AS exhibits a greater decline in voluntary activation during fatiguing contractions than elbow flexor muscles. This is not accompanied by peripheral changes, which implies central mechanisms are responsible. Thus, we conclude that AS is susceptible to central fatigue during maximal voluntary activations. We propose this may be a protective mechanism to conserve contractile potential of the anal sphincter for function. Neurourol. Urodynam. Neurourol. Urodynam. 30: 1550–1556, 2011.
Keyword Continence
Neuromuscular fatigue
Training
Transcranial magnetic stimulation
Q-Index Code C1
Q-Index Status Confirmed Code
Grant ID 601201
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: Official 2012 Collection
School of Health and Rehabilitation Sciences Publications
 
Versions
Version Filter Type
Citation counts: TR Web of Science Citation Count  Cited 5 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 5 times in Scopus Article | Citations
Google Scholar Search Google Scholar
Created: Sun, 27 Nov 2011, 16:45:01 EST by System User on behalf of School of Health & Rehabilitation Sciences