| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 Exercise Science, University of Massachusetts, Amherst, MA, USA
* To whom correspondence should be addressed. E-mail: kamen{at}excsci.umass.edu.
The purpose of this study was to investigate the occurrence of motor unit doublet discharges in young and older individuals at different rates of increasing force. Participants included eight young (21.9±3.56 years) and eight older (74.1±8.79 years) individuals, with equal numbers of males and females in each group. Motor unit activity was recorded from the tibialis anterior during isometric dorsiflexion using a four-wire needle electrode. Subjects performed three ramp contractions from zero to 50% maximal voluntary contraction (MVC) force at each of three rates: 10%, 30% and 50% MVC/s. Overall, the occurrence of doublets was significantly higher in the young than in the older individuals. However, neither group showed differences in the occurrence of doublets across the three rates of force production. Doublet firings were observed in 45.6% (young) and 35.1% (old) of motor units at 10% MVC/s; 48.6% (young) and 22.5% (old) of motor units at 30% MVC/s; and 48.4% (young) and 31.4% (old) at 50% MVC/s. The maximal firing rate was significantly higher and the force at which the motor units were recruited was significantly lower for those units that fired doublets than those that did not. The force at which doublets occurred ranged from 3.42% to 50% MVC in the young subjects and from 0% (force onset) to 50% MVC in the older subjects. The results of this study suggest that the occurrence of doublets is dependent on both motor unit firing rate and force level. The lower incidence of doublets in older individuals may be attributable to changes in the intrinsic properties of the motoneurons with aging, which appear to play a role in doublet discharges.
This article has been cited by other articles:
|
|
 |
|
  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]
|
|
|
|
 |
|
 D. Farina, M. Pozzo, M. Lanzetta, and R. M. Enoka Discharge Variability of Motor Units in an Intrinsic Muscle of Transplanted Hand J Neurophysiol, May 1, 2008; 99(5): 2232 - 2240. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Klass, S. Baudry, and J. Duchateau Age-related decline in rate of torque development is accompanied by lower maximal motor unit discharge frequency during fast contractions J Appl Physiol, March 1, 2008; 104(3): 739 - 746. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Piotrkiewicz, L. Kudina, J. Mierzejewska, M. Jakubiec, and I. Hausmanowa-Petrusewicz Age-related change in duration of afterhyperpolarization of human motoneurones J. Physiol., December 1, 2007; 585(2): 483 - 490. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
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]
|
|
|
|
|
|
R. D. Maladen, R. Perumal, A. S. Wexler, and S. A. Binder-Macleod Effects of activation pattern on nonisometric human skeletal muscle performance J Appl Physiol, May 1, 2007; 102(5): 1985 - 1991. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH |
| Visit Other APS Journals Online |
