Journal of Applied Physiology
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J Appl Physiol 105: 637-642, 2008. First published June 12, 2008; doi:10.1152/japplphysiol.90332.2008
8750-7587/08 $8.00
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Muscle fiber size and function in elderly humans: a longitudinal study

Walter R. Frontera,1,2,3 Kieran F. Reid,1 Edward M. Phillips,1,2 Lisa S. Krivickas,2 Virginia A. Hughes,4 Ronenn Roubenoff,1 and Roger A. Fielding1,2

1Nutrition, Exercise Physiology, and Sarcopenia Laboratory, Jean Mayer United States Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston; and 2Department of Physical Medicine and Rehabilitation, Harvard Medical School and Spaulding Rehabilitation Hospital, Boston, Massachusetts; 3Departments of Physical Medicine and Rehabilitation and Physiology, University of Puerto Rico School of Medicine, San Juan, Puerto Rico; and 4Reproductive Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts

Submitted 27 February 2008 ; accepted in final form 11 June 2008

Cross-sectional studies are likely to underestimate age-related changes in skeletal muscle strength and mass. The purpose of this longitudinal study was to assess whole muscle and single muscle fiber alterations in the same cohort of 12 older (mean age: start of study 71.1 ± 5.4 yr and end of study 80 ± 5.3 yr) volunteers (5 men) evaluated 8.9 yr apart. No significant changes were noted at follow-up in body weight, body mass index, and physical activity. Muscle strength, evaluated using isokinetic dynamometry, and whole muscle specific force of the knee extensors were significantly lower at follow-up. This was accompanied by a significant reduction (5.7%) in cross-sectional area of the total anterior muscle compartment of the thigh as evaluated by computed tomography. Muscle histochemistry showed no significant changes in fiber type distribution or fiber area. Experiments with chemically skinned single muscle fibers (n = 411) demonstrated no change in type I fiber size but an increase in IIA fiber diameter. A trend toward an increase in maximal force in both fiber types was observed. Maximum unloaded shortening velocity did not change. In conclusion, single muscle fiber contractile function may be preserved in older humans in the presence of significant alterations at the whole muscle level. This suggests that surviving fibers compensate to partially correct muscle size deficits in an attempt to maintain optimal force-generating capacity.

aging; compensatory hypertrophy; single muscle fibers


Address for reprint requests and other correspondence: R. A. Fielding, Nutrition, Exercise Physiology, and Sarcopenia Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts Univ., 711 Washington St., Boston, MA 02111 (e-mail: roger.fielding{at}tufts.edu)






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