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This Article Full Text Full Text (PDF) All Versions of this Article: 91/2/457    most recent expphysiol.2005.032771v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Martel, G. F. Articles by Rogers, M. A. Search for Related Content PubMed PubMed Citation Articles by Martel, G. F. Articles by Rogers, M. A. Related Collections Muscle

¹ Department of Physical Therapy, University of Maryland Eastern Shore, Princess Anne, MD, USA² Department of Kinesiology, University of Maryland, College Park, MD, USA³ Division of Gerontology, University of Maryland School of Medicine, and the Baltimore VA GRECC, Baltimore, MD, USA⁴ Department of Kinesiology, Michigan State University, East Lansing, MI, USA⁵ Department of Health and Exercise Science, Colorado State University, Fort Collins, CO, USA⁶ Clinical Research Branch, National Institute on Ageing, Baltimore, MD, USA

This study assessed age and sex effects on muscle fibre adaptations to heavy-resistance strength training (ST). Twenty-two young men and women (20–30 years old) and 18 older men and women (65–75 years old) completed 9 weeks of heavy-resistance knee extension exercises with the dominant leg 3 days week^–1; the non-dominant leg served as a within-subject, untrained control. Bilateral vastus lateralis muscle biopsies were obtained before and after ST for analysis of type I, IIa and IIx muscle fibre cross-sectional area (CSA) and fibre type distribution. One-repetition maximum (1-RM) strength was also assessed before and after ST. ST resulted in increased CSA of type I, IIa and IIx muscle fibres in the trained leg of young men, type I and IIa fibres in young women, type IIa fibres in older men, and type IIx fibres in older women (all P < 0.05). Analysis of fibre type distribution revealed a significant increase in the percentage of type I fibres (P < 0.05) along with a decrease in type IIx fibres (P= 0.054) after ST only in young women. There were no significant changes in muscle fibre CSA or fibre type distribution in the untrained leg for any group. All groups displayed significant increases in 1-RM (27–39%; all P < 0.01). In summary, ST led to significant increases in 1-RM and type II fibre CSA in all groups; however, age and sex influence specific muscle fibre subtype responses to ST.

(Received 15 November 2005; accepted after revision 22 December 2005; first published online 11 January 2005)
Corresponding author G. F. Martel: Department of Physical Therapy, University of Maryland Eastern Shore, Princess Anne, MD 21853, USA. Email: gfmartel{at}mail.umes.edu

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