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The Journals of Gerontology Series A: Biological Sciences and Medical Sciences 59:B108-B117 (2004)
© 2004 The Gerontological Society of America

Fiber Atrophy and Hypertrophy in Skeletal Muscles of Late Middle-Aged Fischer 344 x Brown Norway F1-Hybrid Rats

Russell T. Hepple1,2, Karen D. Ross1 and Amanda B. Rempfer1

1 Faculty of Kinesiology
2 Faculty of Medicine, University of Calgary, Alberta, Canada.

We examined young adult and late middle-aged male rats to test the hypothesis that gastrocnemius (a locomotor muscle) demonstrates reduced fiber size with aging, whereas soleus (a postural muscle) demonstrates atrophy of some fibers and compensatory hypertrophy in other fibers. Although body mass was greater in late middle-aged animals, mass was reduced in gastrocnemius but not soleus muscle. In another group of animals, physical activity was reduced by 34% in late middle-aged animals. Whereas mean fiber size was lower in gastrocnemius of late middle-aged animals, it was not different in soleus. Histograms revealed atrophied fibers (<=1000 µm2) in soleus and gastrocnemius and hypertrophied fibers (>=8000 µm2) in soleus with aging. Atrophied fibers often demonstrated no subsarcolemmal mitochondrial staining, suggesting denervation, whereas hypertrophied fibers often demonstrated cytochrome oxidase deficiency, suggesting mitochondrial dysfunction. These results underscore the divergent influences (e.g., physical inactivity, denervation, mitochondrial dysfunction) affecting fiber size with aging.




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Copyright © 2004 by The Gerontological Society of America.