Document Detail

Implications of group III and IV muscle afferents for high-intensity endurance exercise performance in humans.
MedLine Citation:
PMID:  21878520     Owner:  NLM     Status:  MEDLINE    
We investigated the influence of group III/IV muscle afferents on peripheral fatigue, central motor drive (CMD) and endurance capacity during high-intensity leg-cycling. In a double-blind, placebo-controlled design, seven males performed constant-load cycling exercise (318 ± 9 W; 80% of peak power output (W(peak))) to exhaustion under placebo conditions and with lumbar intrathecal fentanyl impairing spinal μ-opioid receptor-sensitive group III/IV muscle afferents. Peripheral fatigue was assessed via changes in pre- vs. post-exercise quadriceps force in response to supramaximal magnetic femoral nerve stimulation (ΔQ(tw,pot)). CMD was estimated via quadriceps electromyogram. To rule out a direct central effect of fentanyl, we documented unchanged resting cardioventilatory responses. Compared to placebo, significant hypoventilation during the fentanyl trial was indicated by the 9% lower V(E)/V(CO(2)), causing a 5 mmHg increase in end-tidal P(CO(2)) and a 3% lower haemoglobin saturation. Arterial pressure and heart rate averaged 8 and 10% lower, respectively, during the fentanyl trial and these differences progressively diminished towards end-exercise. Although initially similar, the percent change in CMD was 9 ± 3% higher at end-exercise with fentanyl vs. placebo (P < 0.05). Time to exhaustion was shorter (6.8 ± 0.3 min vs. 8.7 ± 0.3 min) and end-exercise ΔQ(tw,pot) was about one-third greater (-44 ± 2% vs. -34 ± 2%) following fentanyl vs. placebo. The rate of peripheral fatigue development was 67 ± 10% greater during the fentanyl trial (P < 0.01). Our findings suggest that feedback from group III/IV muscle afferents limits CMD but also minimizes locomotor muscle fatigue development by stimulating adequate ventilatory and circulatory responses to exercise. In the face of blocked group III/IV muscle afferents, CMD is less inhibited but O(2) transport compromised and locomotor muscle fatigability is exacerbated with a combined net effect of a reduced endurance performance.
Markus Amann; Gregory M Blain; Lester T Proctor; Joshua J Sebranek; David F Pegelow; Jerome A Dempsey
Publication Detail:
Type:  Clinical Trial; Journal Article; Research Support, N.I.H., Extramural     Date:  2011-08-30
Journal Detail:
Title:  The Journal of physiology     Volume:  589     ISSN:  1469-7793     ISO Abbreviation:  J. Physiol. (Lond.)     Publication Date:  2011 Nov 
Date Detail:
Created Date:  2011-11-01     Completed Date:  2012-05-29     Revised Date:  2013-06-27    
Medline Journal Info:
Nlm Unique ID:  0266262     Medline TA:  J Physiol     Country:  England    
Other Details:
Languages:  eng     Pagination:  5299-309     Citation Subset:  IM    
University of Utah, Department of Internal Medicine, Salt Lake City, UT, USA.
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MeSH Terms
Analgesics, Opioid / pharmacology
Exercise / physiology*
Fentanyl / pharmacology
Heart Rate / drug effects
Magnetic Field Therapy
Muscle Fatigue / physiology*
Muscle Fibers, Skeletal / physiology*
Physical Endurance
Pulmonary Ventilation / drug effects
Quadriceps Muscle / physiology*
Young Adult
Grant Support
Reg. No./Substance:
0/Analgesics, Opioid; 437-38-7/Fentanyl

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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