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Muscle Fiber Type Transitions with Exercise Training: Shifting Perspectives

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 II...

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Autores principales: Plotkin, Daniel L., Roberts, Michael D., Haun, Cody T., Schoenfeld, Brad J.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2021
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8473039/
https://www.ncbi.nlm.nih.gov/pubmed/34564332
http://dx.doi.org/10.3390/sports9090127
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author Plotkin, Daniel L.
Roberts, Michael D.
Haun, Cody T.
Schoenfeld, Brad J.
author_facet Plotkin, Daniel L.
Roberts, Michael D.
Haun, Cody T.
Schoenfeld, Brad J.
author_sort Plotkin, Daniel L.
collection PubMed
description 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.
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spelling pubmed-84730392021-09-28 Muscle Fiber Type Transitions with Exercise Training: Shifting Perspectives Plotkin, Daniel L. Roberts, Michael D. Haun, Cody T. Schoenfeld, Brad J. Sports (Basel) Review 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. MDPI 2021-09-10 /pmc/articles/PMC8473039/ /pubmed/34564332 http://dx.doi.org/10.3390/sports9090127 Text en © 2021 by the authors. https://creativecommons.org/licenses/by/4.0/Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
spellingShingle Review
Plotkin, Daniel L.
Roberts, Michael D.
Haun, Cody T.
Schoenfeld, Brad J.
Muscle Fiber Type Transitions with Exercise Training: Shifting Perspectives
title Muscle Fiber Type Transitions with Exercise Training: Shifting Perspectives
title_full Muscle Fiber Type Transitions with Exercise Training: Shifting Perspectives
title_fullStr Muscle Fiber Type Transitions with Exercise Training: Shifting Perspectives
title_full_unstemmed Muscle Fiber Type Transitions with Exercise Training: Shifting Perspectives
title_short Muscle Fiber Type Transitions with Exercise Training: Shifting Perspectives
title_sort muscle fiber type transitions with exercise training: shifting perspectives
topic Review
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8473039/
https://www.ncbi.nlm.nih.gov/pubmed/34564332
http://dx.doi.org/10.3390/sports9090127
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