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

2011; Lippincott Williams & Wilkins; Volume: 26; Issue: 6 Linguagem: Inglês

10.1519/jsc.0b013e318234eb6f

1533-4287

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

Muscle Physiology and Disorders

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.