Eccentric Exercise Increases Satellite Cell Content in Type II Muscle Fibers

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 +/- 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 +/- 0.012 to 0.133 +/- 0.016 SCs per fiber, respectively; P < 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 +/- 0.008 to 0.070 +/- 0.017 SCs per muscle fiber P < 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.