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Exercise pattern influences skeletal muscle hybrid fibers of runners and nonrunners.
Med Sci Sports Exerc. 2007 Nov; 39(11):1977-84.MS

Abstract

PURPOSE

To determine whether relationships between skeletal muscle hybrid fiber composition and whole-body exercise patterns help to elucidate their transitional capacity or a fine-tuning response to functional demands.

METHODS

This study investigated hybrid fibers from vastus lateralis biopsies of runners (N= 13) and nonrunners (N = 9) and related hybrid fiber occurrence and distribution of myosin heavy-chain isoforms (MHC) within hybrid fibers to exercise patterns. MHC composition of single fibers was identified by SDS-PAGE.

RESULTS

Runners had more fibers expressing only MHC I, fewer expressing MHC IIx, and fewer IIa/IIx hybrid fibers (P < 0.05). Hybrid IIa/IIx and I/IIa fibers were, respectively, negatively and positively related to training volume or average preferred racing distance (PRDA) in runners (P < 0.05). The relationship between IIa/IIx hybrid fibers and PRDA was more exponential (R(2) = 0.88) than linear (R(2) = 0.69). Only IIa/IIx hybrid fibers correlated negatively with exercise hours in nonrunners (P < 0.05). Their IIa/IIx hybrid fibers had MHC IIa content ranging from 1 to 99%, with most between 41 and 60%. Runners favoring longer distances (PRDA > 8 km or training > 70 km x wk(-1)) had no IIa/IIx hybrid fibers with MHC IIa proportion > 60%. In these runners, MHC I within hybrid I/IIa fibers was skewed toward higher proportions (> 60%), whereas MHC I proportions were skewed oppositely in runners favoring shorter training or racing distances.

CONCLUSIONS

Training volume influences both IIa/IIx and I/IIa hybrid fiber proportions in runners, but only the former in nonrunners. Hybrid IIa/IIx fiber proportions were modulated by racing distance. Distinctly different distributions of MHC isoforms within the hybrid fibers were seen in runners favoring longer distances versus those favoring shorter distances.

Authors+Show Affiliations

Department of Physiological Sciences, University of Stellenbosch, South Africa.No affiliation info availableNo affiliation info available

Pub Type(s)

Comparative Study
Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

17986905

Citation

Kohn, Tertius A., et al. "Exercise Pattern Influences Skeletal Muscle Hybrid Fibers of Runners and Nonrunners." Medicine and Science in Sports and Exercise, vol. 39, no. 11, 2007, pp. 1977-84.
Kohn TA, Essen-Gustavsson B, Myburgh KH. Exercise pattern influences skeletal muscle hybrid fibers of runners and nonrunners. Med Sci Sports Exerc. 2007;39(11):1977-84.
Kohn, T. A., Essen-Gustavsson, B., & Myburgh, K. H. (2007). Exercise pattern influences skeletal muscle hybrid fibers of runners and nonrunners. Medicine and Science in Sports and Exercise, 39(11), 1977-84.
Kohn TA, Essen-Gustavsson B, Myburgh KH. Exercise Pattern Influences Skeletal Muscle Hybrid Fibers of Runners and Nonrunners. Med Sci Sports Exerc. 2007;39(11):1977-84. PubMed PMID: 17986905.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Exercise pattern influences skeletal muscle hybrid fibers of runners and nonrunners. AU - Kohn,Tertius A, AU - Essen-Gustavsson,Birgitta, AU - Myburgh,Kathryn H, PY - 2007/11/8/pubmed PY - 2008/2/15/medline PY - 2007/11/8/entrez SP - 1977 EP - 84 JF - Medicine and science in sports and exercise JO - Med Sci Sports Exerc VL - 39 IS - 11 N2 - PURPOSE: To determine whether relationships between skeletal muscle hybrid fiber composition and whole-body exercise patterns help to elucidate their transitional capacity or a fine-tuning response to functional demands. METHODS: This study investigated hybrid fibers from vastus lateralis biopsies of runners (N= 13) and nonrunners (N = 9) and related hybrid fiber occurrence and distribution of myosin heavy-chain isoforms (MHC) within hybrid fibers to exercise patterns. MHC composition of single fibers was identified by SDS-PAGE. RESULTS: Runners had more fibers expressing only MHC I, fewer expressing MHC IIx, and fewer IIa/IIx hybrid fibers (P < 0.05). Hybrid IIa/IIx and I/IIa fibers were, respectively, negatively and positively related to training volume or average preferred racing distance (PRDA) in runners (P < 0.05). The relationship between IIa/IIx hybrid fibers and PRDA was more exponential (R(2) = 0.88) than linear (R(2) = 0.69). Only IIa/IIx hybrid fibers correlated negatively with exercise hours in nonrunners (P < 0.05). Their IIa/IIx hybrid fibers had MHC IIa content ranging from 1 to 99%, with most between 41 and 60%. Runners favoring longer distances (PRDA > 8 km or training > 70 km x wk(-1)) had no IIa/IIx hybrid fibers with MHC IIa proportion > 60%. In these runners, MHC I within hybrid I/IIa fibers was skewed toward higher proportions (> 60%), whereas MHC I proportions were skewed oppositely in runners favoring shorter training or racing distances. CONCLUSIONS: Training volume influences both IIa/IIx and I/IIa hybrid fiber proportions in runners, but only the former in nonrunners. Hybrid IIa/IIx fiber proportions were modulated by racing distance. Distinctly different distributions of MHC isoforms within the hybrid fibers were seen in runners favoring longer distances versus those favoring shorter distances. SN - 0195-9131 UR - https://www.unboundmedicine.com/medline/citation/17986905/Exercise_pattern_influences_skeletal_muscle_hybrid_fibers_of_runners_and_nonrunners_ L2 - https://doi.org/10.1249/mss.0b013e3181453546 DB - PRIME DP - Unbound Medicine ER -