JN AJP: Advances in Physiology Education
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

J Neurophysiol 84: 358-366, 2000;
0022-3077/00 $5.00
This Article
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Web of Science (42)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Semmler, J. G.
Right arrow Articles by Enoka, R. M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Semmler, J. G.
Right arrow Articles by Enoka, R. M.

The Journal of Neurophysiology Vol. 84 No. 1 July 2000, pp. 358-366
Copyright ©2000 by the American Physiological Society

Motor-Unit Synchronization Is Not Responsible for Larger Motor-Unit Forces in Old Adults

John G. Semmler, Julie W. Steege, Kurt W. Kornatz, and Roger M. Enoka

Department of Kinesiology and Applied Physiology, University of Colorado, Boulder, Colorado 80309-0354

Semmler, John G., Julie W. Steege, Kurt W. Kornatz, and Roger M. Enoka. Motor-Unit Synchronization Is Not Responsible for Larger Motor-Unit Forces in Old Adults. J. Neurophysiol. 84: 358-366, 2000. Motor-unit synchronization, which is a measure of the near simultaneous discharge of action potentials by motor units, has the potential to influence spike-triggered average force and the steadiness of a low-force isometric contraction. The purpose of the study was to estimate the contribution of motor-unit synchronization to the larger spike-triggered average forces and the decreased steadiness exhibited by old adults. Eleven young (age 19-30 yr) and 14 old (age 63-81 yr) adults participated in the study. Motor-unit activity was recorded with two fine-wire intramuscular electrodes in the first dorsal interosseus muscle during isometric contractions that caused the index finger to exert an abduction force. In a separate session, steadiness measurements were obtained during constant-force isometric contractions at target forces of 2.5, 5, 7.5, and 10% of the maximum voluntary contraction (MVC) force. Mean (±SD) motor-unit forces measured by spike-triggered averaging were larger in old (15.5 ± 12.1 mN) compared with young (7.3 ± 5.7 mN) adults, and the differences were more pronounced between young (8.7 ± 6.4 mN) and old (19.9 ± 12.2 mN) men. Furthermore, the old adults had a reduced ability to maintain a steady force during an isometric contraction, particularly at low target forces (2.5 and 5% MVC). Mean (±SD) motor-unit synchronization, expressed as the frequency of extra synchronous discharges above chance in the cross-correlogram, was similar in young [0.66 ± 0.4 impulses/s (imp/s); range, 0.35-1.51 imp/s; 53 pairs) and old adults (0.72 ± 0.5 imp/s; range, 0.27-1.38 imp/s; 56 pairs). The duration of synchronous peaks in the cross-correlogram was similar for each group (~16 ms). These data suggest that motor-unit synchronization is not responsible for larger spike-triggered average forces in old adults and that motor-unit synchronization does not contribute to the decreased steadiness of low-force isometric contractions observed in old adults.




This article has been cited by other articles:


Home page
 J. Appl. Physiol.Home page
P. Contessa, A. Adam, and C. J. De Luca
Motor unit control and force fluctuation during fatigue
J Appl Physiol, July 1, 2009; 107(1): 235 - 243.
[Abstract] [Full Text] [PDF]

Home page
 Journals of Gerontology Series A: Biological Sciences and Medical SciencesHome page
B. C. Clark and T. M. Manini
Sarcopenia != Dynapenia
J. Gerontol. A Biol. Sci. Med. Sci., August 1, 2008; 63(8): 829 - 834.
[Abstract] [Full Text] [PDF]

Home page
 J. Neurophysiol.Home page
S. A. Winges, K. W. Kornatz, and M. Santello
Common Input to Motor Units of Intrinsic and Extrinsic Hand Muscles During Two-Digit Object Hold
J Neurophysiol, March 1, 2008; 99(3): 1119 - 1126.
[Abstract] [Full Text] [PDF]

Home page
 J. Neurophysiol.Home page
B. K. Barry, M. A. Pascoe, M. Jesunathadas, and R. M. Enoka
Rate Coding Is Compressed But Variability Is Unaltered for Motor Units in a Hand Muscle of Old Adults
J Neurophysiol, May 1, 2007; 97(5): 3206 - 3218.
[Abstract] [Full Text] [PDF]

Home page
 J. Appl. Physiol.Home page
C. A. Knight and G. Kamen
Modulation of motor unit firing rates during a complex sinusoidal force task in young and older adults
J Appl Physiol, January 1, 2007; 102(1): 122 - 129.
[Abstract] [Full Text] [PDF]

Home page
 J. Appl. Physiol.Home page
K. G. Keenan, D. Farina, R. Merletti, and R. M. Enoka
Amplitude cancellation reduces the size of motor unit potentials averaged from the surface EMG
J Appl Physiol, June 1, 2006; 100(6): 1928 - 1937.
[Abstract] [Full Text] [PDF]

Home page
 J. Neurophysiol.Home page
C. N. Christakos, N. A. Papadimitriou, and S. Erimaki
Parallel Neuronal Mechanisms Underlying Physiological Force Tremor in Steady Muscle Contractions of Humans
J Neurophysiol, January 1, 2006; 95(1): 53 - 66.
[Abstract] [Full Text] [PDF]

Home page
 J. Neurophysiol.Home page
C. J. Mottram, E. A. Christou, F. G. Meyer, and R. M. Enoka
Frequency Modulation of Motor Unit Discharge Has Task-Dependent Effects on Fluctuations in Motor Output
J Neurophysiol, October 1, 2005; 94(4): 2878 - 2887.
[Abstract] [Full Text] [PDF]

Home page
 J. Neurophysiol.Home page
C. T. Moritz, E. A. Christou, F. G. Meyer, and R. M. Enoka
Coherence at 16-32 Hz Can Be Caused by Short-Term Synchrony of Motor Units
J Neurophysiol, July 1, 2005; 94(1): 105 - 118.
[Abstract] [Full Text] [PDF]

Home page
 J. Neurophysiol.Home page
M. M. Sturman, D. E. Vaillancourt, and D. M. Corcos
Effects of Aging on the Regularity of Physiological Tremor
J Neurophysiol, June 1, 2005; 93(6): 3064 - 3074.
[Abstract] [Full Text] [PDF]

Home page
 J. Neurophysiol.Home page
K. T. Reilly, M. A. Nordstrom, and M. H. Schieber
Short-Term Synchronization Between Motor Units in Different Functional Subdivisions of the Human Flexor Digitorum Profundus Muscle
J Neurophysiol, August 1, 2004; 92(2): 734 - 742.
[Abstract] [Full Text] [PDF]

Home page
 Journals of Gerontology Series A: Biological Sciences and Medical SciencesHome page
B. K. Barry and R. G. Carson
The Consequences of Resistance Training for Movement Control in Older Adults
J. Gerontol. A Biol. Sci. Med. Sci., July 1, 2004; 59(7): M730 - M754.
[Abstract] [Full Text] [PDF]

Home page
 J. Appl. Physiol.Home page
M. Shinohara, M. L. Latash, and V. M. Zatsiorsky
Age effects on force produced by intrinsic and extrinsic hand muscles and finger interaction during MVC tasks
J Appl Physiol, October 1, 2003; 95(4): 1361 - 1369.
[Abstract] [Full Text] [PDF]

Home page
 J. Neurophysiol.Home page
J. G. Semmler, K. W. Kornatz, and R. M. Enoka
Motor-Unit Coherence During Isometric Contractions Is Greater in a Hand Muscle of Older Adults
J Neurophysiol, August 1, 2003; 90(2): 1346 - 1349.
[Abstract] [Full Text] [PDF]

Home page
 J. Neurophysiol.Home page
A. M. Taylor, E. A. Christou, and R. M. Enoka
Multiple Features of Motor-Unit Activity Influence Force Fluctuations During Isometric Contractions
J Neurophysiol, August 1, 2003; 90(2): 1350 - 1361.
[Abstract] [Full Text] [PDF]

Home page
 J. Appl. Physiol.Home page
D. H. Laidlaw, S. K. Hunter, and R. M. Enoka
Nonuniform activation of the agonist muscle does not covary with index finger acceleration in old adults
J Appl Physiol, October 1, 2002; 93(4): 1400 - 1410.
[Abstract] [Full Text] [PDF]

Home page
 J. Appl. Physiol.Home page
E. A. Christou and L. G. Carlton
Age and contraction type influence motor output variability in rapid discrete tasks
J Appl Physiol, August 1, 2002; 93(2): 489 - 498.
[Abstract] [Full Text] [PDF]

Home page
 J. Appl. Physiol.Home page
B. L. Tracy and R. M. Enoka
Older adults are less steady during submaximal isometric contractions with the knee extensor muscles
J Appl Physiol, March 1, 2002; 92(3): 1004 - 1012.
[Abstract] [Full Text] [PDF]

Home page
 Journals of Gerontology Series A: Biological Sciences and Medical SciencesHome page
E. A. Christou and L. G. Carlton
Old Adults Exhibit Greater Motor Output Variability Than Young Adults Only During Rapid Discrete Isometric Contractions
J. Gerontol. A Biol. Sci. Med. Sci., December 1, 2001; 56(12): B524 - 532.
[Abstract] [Full Text] [PDF]


HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Visit Other APS Journals Online