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

lingua: Inglese

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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