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The Effects of Endurance, Strength, and Power Training on Muscle Fiber Type Shifting

Wilson, Jacob M.; Loenneke, Jeremy P.; Jo, Edward; Wilson, Gabriel J.; Zourdos, Michael C.; Kim, Jeong-Su

Journal of Strength & Conditioning Research: June 2012 - Volume 26 - Issue 6 - p 1724–1729
doi: 10.1519/JSC.0b013e318234eb6f
Brief Review

Abstract: Wilson, JM, Loenneke, JP, Jo, E, Wilson, GJ, Zourdos, MC, and Kim, J.-S. The effects of endurance, strength, and power training on muscle fiber type shifting. J Strength Cond Res 26(6): 1724–1729, 2012—Muscle fibers are generally fractionated into type I, IIA, and IIX fibers. Type I fibers specialize in long duration contractile activities and are found in abundance in elite endurance athletes. Conversely type IIA and IIX fibers facilitate short-duration anaerobic activities and are proportionally higher in elite strength and power athletes. A central area of interest concerns the capacity of training to increase or decrease fiber types to enhance high-performance activities. Although interconversions between type IIA and IIX are well recognized in the literature, there are conflicting studies regarding the capacity of type I and II fibers to interconvert. Therefore, the purpose of this article is to analyze the effects of various forms of exercise on type I and type II interconversions. Possible variables that may increase type II fibers and decrease type I fibers are discussed, and these include high velocity isokinetic contractions; ballistic movements such as bench press throws and sprints. Conversely, a shift from type II to type I fibers may occur under longer duration, higher volume endurance type events. Special care is taken to provide practical applications for both the scientist and the athlete.

1Department of Health Sciences and Human Performance, The University of Tampa, Tampa, Florida

2Department of Health and Exercise Science, The University of Oklahoma, Norman, Oklahoma

3Department of Nutrition, Food, and Exercise Sciences, The Florida State University, Tallahassee, Florida

4Department of Nutritional Sciences, University of Illinois, Champaign-Urbana, Illinois

Address correspondence to Jacob M. Wilson,

Copyright © 2012 by the National Strength & Conditioning Association.