HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Free Full Text (PDF) Free All Versions of this Article: 95/1/373    most recent 00060.2003v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (16) Citing Articles via Google Scholar Google Scholar Articles by Christou, E. A. Articles by Enoka, R. M. Search for Related Content PubMed PubMed Citation Articles by Christou, E. A. Articles by Enoka, R. M.

Fluctuations in acceleration during voluntary contractions lead to greater impairment of movement accuracy in old adults

Department of Kinesiology and Applied Physiology, University of Colorado at Boulder, Boulder, Colorado 80309

Submitted 22 January 2003 ; accepted in final form 14 March 2003

The purpose of the study was to assess the effect of movement velocity on the relation between fluctuations in acceleration and the ability to achieve a target velocity during voluntary contractions performed by young (29.5 ± 4.3 yr) and old (74.9 ± 6.2 yr) adults. Subjects performed concentric and eccentric contractions with the first dorsal interosseus muscle while lifting a submaximal load (15% of maximum) at six movement velocities (0.03–1.16 rad/s). Fluctuations in acceleration, the accuracy of matching the target velocity, and electromyographic (EMG) activity were determined from three trials for each contraction type and movement velocity. The fluctuations in acceleration increased with movement velocity for both concentric and eccentric contractions, but they were greatest during fast eccentric contractions (135%) when there was stronger modulation of acceleration in the 5- to 10-Hz bandwidth. Nonetheless, EMG amplitude for first dorsal interosseus increased with movement velocity only for concentric and not eccentric contractions. Consistent with the minimum variance theory, movement accuracy was related to the fluctuations in acceleration for both types of contractions in all subjects. For a given level of fluctuations in acceleration, however, old subjects were three times less accurate than young subjects. Although the EMG amplitude at each speed was similar for young and old adults, only the young adults modulated the power in the EMG spectrum with speed. Thus the fluctuations in acceleration during voluntary contractions had a more pronounced effect on movement accuracy for old adults compared with young adults, probably due to factors that influenced the frequency-domain characteristics of the EMG.

concentric contraction; eccentric contraction; electromyogram; first dorsal interosseus; frequency spectrum

This article has been cited by other articles:

				T. S. Turner, K. J. Tucker, N. C. Rogasch, and J. G. Semmler Impaired neuromuscular function during isometric, shortening, and lengthening contractions after exercise-induced damage to elbow flexor muscles J Appl Physiol, August 1, 2008; 105(2): 502 - 509. [Abstract] [Full Text] [PDF]

				E. A. Christou, B. Poston, J. A. Enoka, and R. M. Enoka Different Neural Adjustments Improve Endpoint Accuracy With Practice in Young and Old Adults J Neurophysiol, May 1, 2007; 97(5): 3340 - 3350. [Abstract] [Full Text] [PDF]

				K. W. Kornatz, E. A. Christou, and R. M. Enoka Practice reduces motor unit discharge variability in a hand muscle and improves manual dexterity in old adults J Appl Physiol, June 1, 2005; 98(6): 2072 - 2080. [Abstract] [Full Text] [PDF]

				E. A. Christou, J. M. Jakobi, A. Critchlow, M. Fleshner, and R. M. Enoka The 1- to 2-Hz oscillations in muscle force are exacerbated by stress, especially in older adults J Appl Physiol, July 1, 2004; 97(1): 225 - 235. [Abstract] [Full Text] [PDF]