Eccentric exercise increases satellite cell content in type II muscle fibers.

INTRODUCTION: Satellite cells (SCs) are of key importance in skeletal tissue growth, repair, and regeneration. A single bout of high-force exercise has been demonstrated to increase mixed muscle SC content after postexercise recovery. However, little is known about fiber type- in SC content and their activation status within 24 h of postexercise METHODS: Nine recreationally active young men (23 +/- 1 yr) performed eccentric actions of the knee extensors on an isokinetic dynamometer. muscle biopsies from the vastus lateralis were collected preexercise and postexercise. Muscle fiber type-specific SC content and the number of SCs were determined by immunohistochemical analyses. RESULTS: There was difference between Type I and Type II muscle fiber SC content before content significantly increased 24 h postexercise in Type II muscle 0.085 +/- 0.012 to 0.133 +/- 0.016 SCs per fiber, respectively; P < whereas there was no change in Type I fibers. In accordance, activation increased from preexercise to 24 h postexercise as demonstrated by the in the number of DLK1+ SCs in Type II muscle fibers (from 0.027 +/- 0.070 +/- 0.017 SCs per muscle fiber P < 0.05). Although no significant were observed in the number of Ki-67+ SCs, we did observe an increase in number of proliferating cell nuclear antigen-positive SCs after 24 h of postexercise recovery. CONCLUSION: A single bout of high-force eccentric increases muscle fiber SC content and activation status in Type II but muscle fibers.