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Force deficits of human type I, IIa, and IIa/IIx muscle fibers following a single in vitro eccentric contraction
Author(s) -
Choi SeungJun,
Widrick Jeffrey J
Publication year - 2010
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.24.1_supplement.989.18
Subject(s) - isometric exercise , eccentric , contraction (grammar) , myofibril , myosin , chemistry , medicine , muscle contraction , fiber , fiber type , endocrinology , anatomy , biophysics , biochemistry , biology , physics , quantum mechanics , organic chemistry
Fast muscles from small laboratory animals show greater force deficits after eccentric contractions than slow muscles. How this applies to humans is unclear as humans do not express the same fast myosin heavy chain (MHC) isoforms as these animal models. To investigate relationships between eccentric damage and fiber type in human muscle, we measured peak Ca 2+ activated force (15°C) of chemically skinned fiber segments (vastus lateralis, 6 subjects, age = 24 ± 2) before and after a single eccentric contraction (25% strain, 50% of pre‐eccentric unloaded shortening velocity). Fiber type was determined by gel electrophoresis. Fibers showing visible post‐eccentric myofibrillar tearing (N = 8) were excluded from analysis. At baseline, type IIa (125 ± 6 kN/m 2 ; n = 28) and IIa/IIx (133 ± 7 kN/m 2 ; n = 12) fibers produced greater Ca 2+ activated force than type I fibers (111 ± 3 kN/m 2 ; n = 38). A significant fiber type × time interaction revealed similar force deficits for type I (11 ± 1 kN/m 2 or 10 ± 1% of pre force) and IIa (14 ± 2 kN/m 2 , 11 ± 1%) fibers but a 3‐fold greater deficit for IIa/IIx fibers (40 ± 5 kN/m 2 , 30 ± 3%). Control fibers subjected to a single isometric contraction showed force deficits of only 2 ± 1 kN/m 2 (1 ± 1 %) with no difference between fiber types. These results indicate that human fast hybrid fibers (IIa/IIx) are more sensitive to a standardized in vitro eccentric contraction then either type I or type IIa fibers.