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The Journal of Sports Medicine and Physical Fitness 2000 December;40(4):284-9

Copyright © 2001 EDIZIONI MINERVA MEDICA

language: English

A decade of aerobic endurance training: histological evidence for fibre type transformation

Thayer R., Collins J., Noble E. G., Taylor A. W.

Human Performance Laboratory and Department of Biology, Lakehead University, Thunder Bay, Ontario, and Faculty of Kinesiology, University of Western Ontario, London, Ontario, Canada


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Back­ground. ­Researchers ­employing a ­variety of ­training ­methods ­have dem­on­strated a ­fast-to-­slow ­fibre trans­for­ma­tion in ­animal skel­etal ­muscle. The obser­va­tion as to ­whether ­this ­occurs in exer­cise ­trained ­humans is lim­ited and equiv­ocal.
­Methods. Experi­mental ­design: to ­examine ­this ­issue, skel­etal ­muscle ­from ­seven sub­jects who had par­tic­i­pated in a ­decade or ­more of ­high inten­sity ­aerobic ­training (DT) and six non-­trained (NT) sub­jects was ­obtained by ­muscle ­biopsy ­from the ­vastus lat­er­alis ­muscle (VL) and sub­jected to a mod­i­fied myo­fi­brillar ­ATPase tech­nique to iden­tify ­muscle ­fibre ­types. ­Muscle ­tissue was his­to­chem­i­cally ­treated by expo­sure to an alka­line pre­in­cu­ba­tion (pH 9.9), an ­acid pre­in­cu­ba­tion (pH 4.3 or 4.6) and the for­mate-KCl pre­in­cu­ba­tion ­buffer (pH 4.54), pre­vi­ously ­employed in ­animal ­studies.
­Results. The for­mate-KCl pre­in­cu­ba­tion ­medium iden­ti­fied all ­major ­fibre ­types at a ­single pH in ­human sub­jects. The per­centage of ­type I ­fibres in DT was 70.9% vs 37.7% in NT (p<0.01), ­while the ­type IIa ­fibres in DT (25.3%) was ­much ­lower (p<0.01) ­than NT (51.8%). Sur­pris­ingly, ­type IIa ­fibres in the DT ­group dis­played ­lesser oxi­da­tive ­staining inten­sity (p<0.01) ­than ­type IIa ­fibres ­from the NT ­group. ­Mean ­cross-sec­tional ­area of ­type I ­fibres for DT (6233.9±1421.7 μm2) was ­greater (p<0.05) ­than ­either ­type I (5746.8±1135.2 μm2) or II (5693.5±1214.6 μm2) ­from NT.
Con­clu­sions. The ­results ­revealed ­that endu­rance ­training may pro­mote a tran­si­tion ­from ­type II to ­type I ­muscle ­fibre ­types and ­occurs at the ­expense of the ­type II ­fibre pop­u­la­tion.

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