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Muscle Fiber Type Transitions with Exercise Training: Shifting Perspectives

1
Health Sciences Department, CUNY Lehman College, Bronx, NY 10468, USA
2
School of Kinesiology, Auburn University, Auburn, AL 36849, USA
3
Fitomics, LLC., Pelham, AL 35124, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Anthony J. Blazevich
Sports 2021, 9(9), 127; https://doi.org/10.3390/sports9090127
Received: 6 July 2021 / Revised: 1 September 2021 / Accepted: 6 September 2021 / Published: 10 September 2021
Human muscle fibers are generally classified by myosin heavy chain (MHC) isoforms characterized by slow to fast contractile speeds. Type I, or slow-twitch fibers, are seen in high abundance in elite endurance athletes, such as long-distance runners and cyclists. Alternatively, fast-twitch IIa and IIx fibers are abundant in elite power athletes, such as weightlifters and sprinters. While cross-sectional comparisons have shown marked differences between athletes, longitudinal data have not clearly converged on patterns in fiber type shifts over time, particularly between slow and fast fibers. However, not all fiber type identification techniques are created equal and, thus, may limit interpretation. Hybrid fibers, which express more than one MHC type (I/IIa, IIa/IIx, I/IIa/IIx), may make up a significant proportion of fibers. The measurement of the distribution of fibers would necessitate the ability to identify hybrid fibers, which is best done through single fiber analysis. Current evidence using the most appropriate techniques suggests a clear ability of fibers to shift between hybrid and pure fibers as well as between slow and fast fiber types. The context and extent to which this occurs, along with the limitations of current evidence, are discussed herein. View Full-Text
Keywords: fast-twitch fibers; slow-twitch fibers; strength training; endurance training fast-twitch fibers; slow-twitch fibers; strength training; endurance training
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MDPI and ACS Style

Plotkin, D.L.; Roberts, M.D.; Haun, C.T.; Schoenfeld, B.J. Muscle Fiber Type Transitions with Exercise Training: Shifting Perspectives. Sports 2021, 9, 127. https://doi.org/10.3390/sports9090127

AMA Style

Plotkin DL, Roberts MD, Haun CT, Schoenfeld BJ. Muscle Fiber Type Transitions with Exercise Training: Shifting Perspectives. Sports. 2021; 9(9):127. https://doi.org/10.3390/sports9090127

Chicago/Turabian Style

Plotkin, Daniel L., Michael D. Roberts, Cody T. Haun, and Brad J. Schoenfeld. 2021. "Muscle Fiber Type Transitions with Exercise Training: Shifting Perspectives" Sports 9, no. 9: 127. https://doi.org/10.3390/sports9090127

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