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Age-Related Differences in the Properties of the Plantar Flexor Muscles and Tendons


Medicine & Science in Sports & Exercise: March 2007 - Volume 39 - Issue 3 - p 541-547
doi: 10.1249/01.mss.0000247006.24965.74
APPLIED SCIENCES: Physical Fitness and Performance

Purpose: The purpose of this study was to determine age-related differences in the human plantar flexor muscles and tendon.

Methods: Four age groups-a 20-yr group (20-27 yr, N = 19), 30-yr group (31-38 yr, N = 15), 50-yr group (46-57 yr, N = 10) and 70-yr group (62-77 yr, N = 15)-volunteered to take part in the present study. Muscle thickness, strength, and activation level (using twitch-interpolation technique) of plantar flexor muscles were measured. Elongation of the Achilles tendon was determined using ultrasonography while subjects performed ramp isometric plantar flexion up to the voluntary maximum.

Results: No significant difference in relative muscle thickness (to limb length) was observed among the four age groups. Muscle strength and activation level of the 20-yr group were significantly higher than those of the 50- and 70-yr groups (activation levels were not measured in the 70-yr group), and maximal strain (elongation/initial tendon length) of the Achilles tendon decreased with aging. Although there were no differences in muscle strength and activation levels between the 20- and 30-yr groups, maximal strain of the Achilles tendon of the 30-yr group was already lower than that of the 20-yr group (P = 0.062).

Conclusion: These results suggest that the processes of age-related changes in the muscle and tendon are different. Furthermore, the differences in age-related changes of muscle and tendon might play a role in the frequency of Achilles tendon ruptures among men in their 30s.

1Department of Life Science, University of Tokyo, Meguro, Tokyo, JAPAN; 2Department of Physical Education, Kokushikan University, Tokyo, JAPAN; and 3Department of Sports Sciences, Waseda University, Tokorozawa, Saitama, JAPAN

Address for correspondence: Keitaro Kubo, Ph.D., Department of Life Science (Sports Sciences), University of Tokyo, Komaba 3-8-1, Meguro-ku, Tokyo 153-8902, Japan; E-mail:

Submitted for publication June 2006.

Accepted for publication October 2006.

©2007The American College of Sports Medicine