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Sex Differences in Single Muscle Fiber Power in Older Adults


Medicine & Science in Sports & Exercise: January 2006 - Volume 38 - Issue 1 - p 57-63
doi: 10.1249/01.mss.0000180357.58329.b1
Basic Sciences: Original Investigations

Purpose: This study was conducted to determine whether differences in power at the single muscle fiber level contribute to sex differences in whole muscle power production in the elderly.

Methods: A total of 16 sedentary older persons (10 women, 6 men), mean age 72 yr, had percutaneous needle biopsy of musculus vastus lateralis. Chemically skinned single muscle fibers were activated with Ca2+ for maximal isometric force measurement (Po). The slack test was performed to determine maximal unloaded shortening velocity (Vo). Force–velocity and power curves were generated via a series of isotonic contractions, allowing measurement of peak power and specific power. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to determine myosin heavy chain composition of single muscle fibers. Whole muscle strength, velocity, and power were measured for knee extension and double leg press.

Results: Men had greater whole muscle strength, power, and velocity compared with women. Studied were 274 type I and 33 type IIa single fibers. No significant sex differences were found for fiber size, Po, specific force, Vo, power, or specific power in type I or IIa fibers.

Conclusions: Single muscle fiber quality in older women is equivalent to that in older men and can not explain the differences seen in whole muscle strength, power, or function.

1Department of Physical Medicine and Rehabilitation, Spaulding Rehabilitation Hospital and Harvard Medical School, Boston, MA; 2Department of Health Sciences, Sargeant College of Health and Rehabilitation Sciences, Boston University, Boston, MA; 3Nutrition, Exercise Physiology, and Sarcopenia Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston, MA; and 4Biostatistics Center, Massachusetts General Hospital, Boston, MA

Address for correspondence: Lisa S. Krivickas, Spaulding Rehabilitation Hospital, 125 Nashua St., Boston, MA 02114; E-mail:

Submitted for publication December 2004.

Accepted for publication July 2005.

This work was supported by NIA grant AG-18844 and this work is based on work supported by the U.S. Department of Agriculture, under agreement No. 58-1950-4-401. Any opinions, findings, conclusion, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

©2006The American College of Sports Medicine