Document Detail

Vastus lateralis single motor unit EMG at the same absolute torque production at different knee angles.
MedLine Citation:
PMID:  19470699     Owner:  NLM     Status:  MEDLINE    
Single motor unit electromyographic (EMG) activity of the knee extensors was investigated at different knee angles with subjects (n = 10) exerting the same absolute submaximal isometric torque at each angle. Measurements were made over a 20 degrees range around the optimum angle for torque production (AngleTmax) and, where feasible, over a wider range (50 degrees ). Forty-six vastus lateralis (VL) motor units were recorded at 20.7 +/- 17.9 %maximum voluntary contraction (%MVC) together with the rectified surface EMG (rsEMG) of the superficial VL muscle. Due to the lower maximal torque capacity at positions more flexed and extended than AngleTmax, single motor unit recruitment thresholds were expected to decrease and discharge rates were expected to increase at angles above and below AngleTmax. Unexpectedly, the recruitment threshold was higher (P < 0.05) at knee angles 10 degrees more extended (43.7 +/- 22.2 N.m) and not different (P > 0.05) at knee angles 10 degrees more flexed (35.2 +/- 17.9 N.m) compared with recruitment threshold at AngleTmax (41.8 +/- 21.4 N.m). Also, unexpectedly the discharge rates were similar (P > 0.05) at the three angles: 11.6 +/- 2.2, 11.6 +/- 2.1, and 12.3 +/- 2.1 Hz. Similar angle independent discharge rates were also found for 12 units (n = 5; 7.4 +/- 5.4 %MVC) studied over the wider (50 degrees ) range, while recruitment threshold only decreased at more flexed angles. In conclusion, the similar recruitment threshold and discharge behavior of VL motor units during submaximal isometric torque production suggests that net motor unit activation did not change very much along the ascending limb of the knee-angle torque relationship. Several factors such as length-dependent twitch potentiation, which may contribute to this unexpected aspect of motor control, are discussed.
T M Altenburg; A de Haan; P W L Verdijk; W van Mechelen; C J de Ruiter
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Publication Detail:
Type:  Journal Article     Date:  2009-05-21
Journal Detail:
Title:  Journal of applied physiology (Bethesda, Md. : 1985)     Volume:  107     ISSN:  8750-7587     ISO Abbreviation:  J. Appl. Physiol.     Publication Date:  2009 Jul 
Date Detail:
Created Date:  2009-07-01     Completed Date:  2009-08-28     Revised Date:  2013-09-26    
Medline Journal Info:
Nlm Unique ID:  8502536     Medline TA:  J Appl Physiol (1985)     Country:  United States    
Other Details:
Languages:  eng     Pagination:  80-9     Citation Subset:  IM    
Institute for Biomedical Research into Human Movement and Health, Manchester Metropolitan University, Cheshire, United Kingdom.
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MeSH Terms
Isometric Contraction / physiology*
Knee / physiology*
Motor Neurons / physiology*
Muscle Stretching Exercises / methods
Quadriceps Muscle / physiology*
Recruitment, Neurophysiological / physiology*

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