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Muscle Fiber Splitting Is a Physiological Response to Extreme Loading in Animals

Murach, Kevin A.1,2; Dungan, Cory M.1,2; Peterson, Charlotte A.1,2; McCarthy, John J.1,3

Exercise and Sport Sciences Reviews: April 2019 - Volume 47 - Issue 2 - p 108–115
doi: 10.1249/JES.0000000000000181

Skeletal muscle fiber branching and splitting typically is associated with damage and regeneration and is considered pathological when observed during loading-induced hypertrophy. We hypothesize that fiber splitting is a nonpathological component of extreme loading and hypertrophy, which is primarily supported by evidence in animals, and propose that the mechanisms and consequences of fiber splitting deserve further exploration.

Skeletal muscle fiber splitting is proposed to be a physiological response to extreme loading and hypertrophy across species and is distinct from regeneration.

1Center for Muscle Biology,

2Department of Rehabilitation Sciences, and

3Department of Physiology, University of Kentucky, Lexington, KY

Address for correspondence: John J. McCarthy, Department of Physiology, College of Medicine, University of Kentucky, 800 Rose St., MS 607A, Lexington, KY 40536 (E-mail:

Accepted for publication: December 18, 2018.

Editor: Marni D. Boppart, Sc.D., FACSM.

© 2019 American College of Sports Medicine