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J Appl Physiol (November 2, 2001). doi:10.1152/japplphysiol.00954.2001
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Articles in PresS, published online ahead of print November 2, 2001
J Appl Physiol, 10.1152/jap.00954.2001
Submitted on September 17, 2001
Accepted on October 28, 2001

Older Adults are Less Steady During Submaximal Isometric Contractions With the Knee Extensor Muscles

Brian L Tracy1* and Roger M Enoka1

1 Kinesiology and Applied Physiology, University of Colorado, Boulder, CO, USA

* To whom correspondence should be addressed. E-mail: tracybl{at}colorado.edu.

This study compared the steadiness of submaximal contractions with the knee extensor muscles in young and old adults. Twenty young and 20 old subjects underwent assessment of isometric maximum voluntary contraction (MVC), one repetition-maximum (1-RM) strength, and steadiness during isometric, concentric, and eccentric contractions with the knee extensor muscles. The old adults displayed 33% lower MVC force and a 41% lower 1-RM load. The coefficient of variation for force was significantly greater for the old adults during isometric contractions at 2, 5, and 10% of MVC, but not at 50% MVC. The decline in steadiness at low forces experienced by the men was marginally greater than that experienced by the women. The steadiness of concentric and eccentric contractions was similar in young and old adults at 5, 10, and 50% of 1-RM load. Old subjects exhibited greater coactivation of an antagonist muscle compared with young subjects during the submaximal isometric and anisometric contractions. These results indicate that whereas the ability to exert steady submaximal forces with the knee extensor muscles was reduced in old adults, fluctuations in knee joint angle during slow movements were similar for young and old adults.




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