Normalized force, activation, and coactivation in the arm muscles of young and old
men.
Rice, C. S. Klein,C. L., and G. D. Marsh .
1Canadian Centre for Activity and Aging, Lawson Health Research Institute, and
2School of Kinesiology, Faculty of Health Sciences, and 3Departments of Anatomy and
Cell Biology, and 4Medical Biophysics, Faculty of Medicine and Dentistry, The
University of Western Ontario, London, Ontario, Canada N6G 2M3
APStracts 8:0308A, 2001.
The purpose of this study was to determine whether the loss of muscle strength in the
elderly could be explained entirely by a decline in the physiological cross-sectional area
(PCSA) of muscle. Isometric force, muscle activation (twitch interpolation), and
coactivation (surface electromyograph) were measured during maximal voluntary
contractions (MVCs) of the elbow flexors (EFs) and extensors (EEs) in 20 young (23 ± 3
yr) and 13 older (81 ± 6 yr) healthy men. PCSA was determined using magnetic
resonance imaging, and normalized force (NF) was calculated as the MVC/PCSA ratio.
The PCSA was smaller in the old compared with the young men, more so in the EEs
(28%) compared with the EFs (19%) (P < 0.001); however, the decline in maximal
isometric force (~30%) with age was similar in the two muscle groups. Muscle activation
was not different between the groups, but coactivation was greater (5%) (P < 0.001) in
the old men for both muscles. NF was less (11%) in the EFs (P < 0.01) and tended to be
unchanged in the EEs of the old compared with young subjects. The relative maintenance
of NF in the EEs compared with the EFs may be related to age-associated changes in the
architecture of the triceps brachii muscle. In conclusion, although the decline in PCSA
explained the majority of strength loss in the old men, additional factors such as greater
coactivation or reduced specific tension also may have contributed to the age-related loss
of isometric strength.
Received 5 March 2001; accepted in final form 18 May 2001
APS Manuscript Number A213-1.
Article publication pending J Appl Physiol
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 29 June 2001