title: Effects of strength, endurance and combined training on myosin heavy chain content and fibre-type distribution in humans.
abstract: This study investigated the effect of strength training, endurance training, and combined strength plus endurance training on fibre-type transitions, fibre cross-sectional area (CSA) and MHC isoform content of the vastus lateralis muscle. Forty volunteers (24 males and 16 females) were randomly assigned to one of four groups: control (C), endurance training (E), strength training (S), or concurrent strength and endurance training (SE). The S and E groups each trained three times a week for 12 weeks; the SE group performed the same S and E training on alternate days. The development of knee extensor muscle strength was S>SE>E ( P<0.05) and has been reported elsewhere. The reduction in knee extensor strength development in SE as compared to S corresponded to a 6% increase in MHCIIa content ( P<0.05) in SE at the expense of the faster MHCIId(x) isoform ( P<0.05), as determined by electrophoretic analyses; reductions in MHCIId/x content after S or E training were attenuated by comparison. Both S and SE induced three- to fourfold reductions ( P<0.05) in the proportion of type IIA/IID(X) hybrid fibres. S also induced fourfold increases in the proportion of type I/IIA hybrid fibres within both genders, and in a population of fibres expressing a type I/IID(X) hybrid phenotype within the male subjects. Type I/IIA hybrid fibres were not detected after SE. Both S and SE training paradigms induced similar increases (16-19%, P<0.05) in the CSA of type IIA fibres. In contrast, the increase in CSA of type I fibres was 2.9-fold greater ( P<0.05) in S as compared to SE after 12 weeks. We conclude that the interference of knee extensor strength development in SE versus S was related to greater fast-to-slow fibre-type transitions and attenuated hypertrophy of type I fibres. Data are given as mean (SEM) unless otherwise stated.
authors.affiliation: Exercise Biochemistry Laboratory, Faculty of Physical Education and Recreation, University of Alberta, T6G 2H9, Edmonton, AB, Canada. tputman@ualberta.ca
authors.forename: Charles T
authors.initials: CT
authors.lastname: Putman
authors.forename: Xinhao
authors.initials: X
authors.lastname: Xu
authors.forename: Ellen
authors.initials: E
authors.lastname: Gillies
authors.forename: Ian M
authors.initials: IM
authors.lastname: MacLean
authors.forename: Gordon J
authors.initials: GJ
authors.lastname: Bell
mesh_terms: D000328:Adult; D004586:Electrophoresis; D005080:Exercise Test; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007536:Isomerism; D035002:Lower Extremity / Q000502:physiology; D008297:Male; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology*; D018657:Muscle Fibers, Slow-Twitch / Q000502:physiology*; D018482:Muscle, Skeletal / Q000166:cytology* / Q000378:metabolism / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000378:metabolism*; D010807:Physical Endurance / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology
chemical_list: D018995:Myosin Heavy Chains