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Medicine & Science in Sports & Exercise:
Basic Sciences: Original Investigations

Sex Differences in Single Muscle Fiber Power in Older Adults

KRIVICKAS, LISA S.1; FIELDING, ROGER A.2,3; MURRAY, ANGELIQUE1; CALLAHAN, DAMIEN2; JOHANSSON, ANDREAS1; DORER, DAVID J.4; FRONTERA, WALTER R.1

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Abstract

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.

©2006The American College of Sports Medicine

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