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CERMAK, N. M., T. SNIJDERS, B. R. MCKAY, G. PARISE, L. B. VERDIJK, M. A. TARNOPOLSKY, M. J. GIBALA, and L. J. C. VAN LOON. Eccentric Exercise Increases Satellite Cell Content in Type II Muscle Fibers. Med. Sci. Sports Exerc., Vol. 45, No. 2, pp. 230–237, 2013. Introduction: Satellite cells (SCs) are of key importance in skeletal muscle tissue growth, repair, and regeneration. A single bout of high-force eccentric exercise has been demonstrated to increase mixed muscle SC content after 1–7 d of postexercise recovery. However, little is known about fiber type–specific changes in SC content and their activation status within 24 h of postexercise recovery. Methods: Nine recreationally active young men (23 T 1 yr) performed 300 eccentric actions of the knee extensors on an isokinetic dynamometer. Skeletal muscle biopsies from the vastus lateralis were collected preexercise and 24 h postexercise. Muscle fiber type–specific SC content and the number of activated SCs were determined by immunohistochemical analyses. Results: There was no difference between Type I and Type II muscle fiber SC content before exercise. SC content significantly increased 24 h postexercise in Type II muscle fibers (from 0.085 T 0.012 to 0.133 T 0.016 SCs per fiber, respectively; P G 0.05), whereas there was no change in Type I fibers. In accordance, activation status increased from preexercise to 24 h postexercise as demonstrated by the increase in the number of DLK1+ SCs in Type II muscle fibers (from 0.027 T 0.008 to 0.070 T 0.017 SCs per muscle fiber P G 0.05). Although no significant changes were observed in the number of Ki-67+ SCs, we did observe an increase in the number of proliferating cell nuclear antigen-positive SCs after 24 h of postexercise recovery. Conclusion: A single bout of high-force eccentric exercise increases muscle fiber SC content and activation status in Type II but not Type I muscle fibers.


Mary MacKillop Institute for Health Research

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