title: Regional adaptation of collagen in skeletal muscle to repeated bouts of strenuous eccentric exercise.
abstract: This study investigated the injured region-specific alterations of factors related to the "repeated bout effect" (RBE), i.e., when the first bout of eccentric exercise generates resistance to injuries from the second bout of the same exercise. Wistar rats were divided into single injury (SI) and repeated injury (RI) groups. The right gastrocnemius muscle was subjected to a bout of eccentric contractions (ECs) at the age of 14 weeks in the SI group and 10 and 14 weeks in the RI group. The number of injured fibers after the last bout of ECs was lower in RI than in SI. In the SI group, injured fibers after ECs were mainly located in the superficial region of muscle and expressed myosin heavy chain (MHC) IIx and IIb. Prior to the second bout of ECs, the fiber-type composition in the RI group showed decreased MHC IIx and IIb fibers and increased MHC IIa fibers compared with those in the SI group. However, most regenerating fibers showed either MHC IIx or IIb expression. Heat shock protein 72 and total collagen contents in whole muscle were higher in the RI group than in the SI group; however, only the collagen expression in the RI group was more intense than that in the SI group in the superficial region of muscle. These findings suggest that increased collagen may play a more important role in the injured region of muscle than the other factors in RBE.
authors.affiliation: Department of Life Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, 153-8902, Japan. ryotakagi1986@yahoo.co.jp.
authors.forename: Ryo
authors.identifier: 0000-0002-8540-7015
authors.initials: R
authors.lastname: Takagi
authors.affiliation: Department of Life and Materials Engineering, Nagoya Institute of Technology, Aichi, Japan.
authors.forename: Riki
authors.initials: R
authors.lastname: Ogasawara
authors.affiliation: Graduate School of Health and Sport Science, Nippon Sport Science University, Tokyo, Japan.
authors.forename: Arata
authors.initials: A
authors.lastname: Tsutaki
authors.affiliation: Graduate School of Health and Sport Science, Nippon Sport Science University, Tokyo, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Nakazato
authors.affiliation: Department of Life Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, 153-8902, Japan.
authors.forename: Naokata
authors.initials: N
authors.lastname: Ishii
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D003094:Collagen / Q000235:genetics / Q000378:metabolism*; D050884:HSP72 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D008297:Male; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000502:physiology; D018995:Myosin Heavy Chains / Q000235:genetics / Q000378:metabolism; D010805:Physical Conditioning, Animal; D051381:Rats; D017208:Rats, Wistar
chemical_list: D050884:HSP72 Heat-Shock Proteins; D003094:Collagen; D018995:Myosin Heavy Chains
keywords: Adaptation; Contraction; Heat shock protein; Myosin heavy chain; Regeneration