Motor units in cranial and caudal regions of the upper trapezius muscle have different discharge rates during brief static contractions.

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Bibliographic Details
Title:	Motor units in cranial and caudal regions of the upper trapezius muscle have different discharge rates during brief static contractions.
Authors:	Falla, D., Farina, D.
Source:	Acta Physiologica. Apr2008, Vol. 192 Issue 4, p551-558. 8p. 4 Graphs.
Subjects:	Motor unit, Trapezius muscle, Muscle contraction, Motor ability, Muscles
Abstract:	Aim: To compare the discharge patterns of motor unit populations from different locations within the upper trapezius muscle during brief submaximal constant-force contractions. Methods: Intramuscular and surface electromyographic (EMG) signals were collected from three sites of the right upper trapezius muscle distributed along the cranial-caudal direction in 11 volunteers during 10 s shoulder abduction at 25% of the maximum voluntary force. Results: A total of 38 motor units were identified at the cranial location, 36 from the middle location and 17 from the caudal location. Initial discharge rate was greatest at the caudal location ( P < 0.05; mean ± SD, cranial: 16.7 ± 3.6 pps, middle: 16.9 ± 4.0 pps, caudal: 19.2 ± 3.3 pps). Discharge rate decreased during the contraction for the most caudal location only ( P < 0.05). Initial estimates of surface EMG root mean square values were highest at the most caudal location ( P < 0.05; cranial: 32.3 ± 20.9 μV, middle: 41.3 ± 21.0 μV, caudal: 51.6 ± 23.6 μV). Conclusion: This study demonstrates non-uniformity of motor unit discharge within the upper trapezius muscle during a brief submaximal constant-force contraction. Location-dependent modulation of discharge rate may reflect spatial dependency in the control of motor units necessary for the development and maintenance of force output. [ABSTRACT FROM AUTHOR]
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Database:	Psychology and Behavioral Sciences Collection

Description
Abstract:	Aim: To compare the discharge patterns of motor unit populations from different locations within the upper trapezius muscle during brief submaximal constant-force contractions. Methods: Intramuscular and surface electromyographic (EMG) signals were collected from three sites of the right upper trapezius muscle distributed along the cranial-caudal direction in 11 volunteers during 10 s shoulder abduction at 25% of the maximum voluntary force. Results: A total of 38 motor units were identified at the cranial location, 36 from the middle location and 17 from the caudal location. Initial discharge rate was greatest at the caudal location ( P < 0.05; mean ± SD, cranial: 16.7 ± 3.6 pps, middle: 16.9 ± 4.0 pps, caudal: 19.2 ± 3.3 pps). Discharge rate decreased during the contraction for the most caudal location only ( P < 0.05). Initial estimates of surface EMG root mean square values were highest at the most caudal location ( P < 0.05; cranial: 32.3 ± 20.9 μV, middle: 41.3 ± 21.0 μV, caudal: 51.6 ± 23.6 μV). Conclusion: This study demonstrates non-uniformity of motor unit discharge within the upper trapezius muscle during a brief submaximal constant-force contraction. Location-dependent modulation of discharge rate may reflect spatial dependency in the control of motor units necessary for the development and maintenance of force output. [ABSTRACT FROM AUTHOR]
ISSN:	17481708
DOI:	10.1111/j.1748-1716.2007.01776.x