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1 The Finnish Centre for Interdisciplinary Gerontology, Jyvaskyla, Finland
2 Department of Clinical Neurophysiology, University of Uppsala, Uppsala, Sweden
3 Department of Health Sciences, University of Jyvaskyla, Jyvaskyla, Sweden
4 Department of Biology and Physical Activity, University of Jyvaskyla, Jyvaskyla, Sweden
5 Department of Biology of Physical Activity, University of Jyvaskyla, Jyvaskyla, Sweden
6 KIHU - Research Institute for Olympic Sports, Jyvaskyla, Finland
7 Department of Health Sciences, University of Jyvaskyla, Jyvaskyla, Finland
* To whom correspondence should be addressed. E-mail: harri.suominen{at}sport.jyu.fi.
Biopsy samples were taken from vastus lateralis of 18-84-yr-old male sprinters (n=91). Fiber type distribution, cross-sectional area and myosin heavy chain (MyHC) isoform content were identified using ATPase histochemistry and SDS-PAGE. Specific tension and maximum shortening velocity (Vo) were determined in 144 single skinned fibers from younger (18-33 yrs, n=8) and older (53-77 yrs, n=9) runners. Force-time characteristics of the knee extensors were determined using isometric contraction. The cross-sectional area of type I fibers was unchanged with age, while that of type II fibers was reduced (P<0.001). With age there was an increased MyHC I (P<0.01) and reduced MyHC IIx isoform content (P<0.05), but no differences in MyHC IIa. Specific tension of type I and IIa MyHC fibers did not differ between younger and older subjects. Vo of fibers expressing type I MyHC was lower (P<0.05) in older than in younger subjects, but there was no difference in Vo of type IIa MyHC fibers. An aging-related decline of maximal isometric force (P<0.001) and normalized rate of force development (RFD) (P<0.05) of knee extensors was observed. Normalized RFD was positively associated with MyHC II (P<0.05). The sprint-trained athletes experienced the typical aging-related reduction in the size of fast fibers, a shift toward a slower MyHC isoform profile and a lower Vo of type I MyHC fibers, which played a role in the decline in explosive force production. However, the muscle characteristics were preserved at a high level in the oldest runners, underlining the favorable impact of sprint exercise on aging muscle.
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