PED 1323 Motor Control & Motor Learning

To an oxidative phenotype within the fast twitch

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to an oxidative phenotype within the fast twitch fiber types (type IIb/x to IIa).” “… Exercise-induced transformation [from type II] to type I fibers remains to be experimentally confirmed.” Why older studies may show fiber type changes not currently believed to be valid based upon modern immunohistochemistry techniques. “… ATPase histochemistry is vulnerable to subtle changes in pH… Caution should be taken when interpreting the data, particularly in regard to changes in type I fibers.” What about a recent study showing increases in % slow twitch fibers with training??? Gehlert S, Weber S, Weidmann B, Gutsche K, Platen P, Graf C, Kappes-Horn K, Bloch W. Cycling exercise-induced myofiber transitions in skeletal muscle depend on basal fiber type distribution. Eur J Appl Physiol. 2011 Oct 29. 21 male cyclists with different performance levels and different initial % slow twitch fibers Trained with increased volume (3.3 hrs/d, 4 d/wk) and reduced power output for 3 months (early season training) Used ATPase staining to determine % fiber types (weak, older technique, see above caution) Results: o Group average data: Cyclists starting with a LOW proportion of slow fibers REDUCED IIa (p=0.01) & INCREASED type I (not sig). o Individual data: 4 Cyclists starting with a 50 – 83% slow fiber DECREASED % type I (!!!!!!!!) Can strength/power Exercise in humans cause HYPERPLASIA (an increase in the number of muscle fibers)? Due to splitting of existing mucle fibers or new fiber formation from satellite cells? G Goldspink and S Harridge, Cellular and Molecular Aspects of Adaptation in Skeletal Muscle. In: Strength and power in sport, 2nd ed. Paavo V. Komi (ed), Malden, MA: Blackwell Science, 2003, pp 231-251. “… animal experiments using normal types of exercise have not shown any changes in the total number of fibres.” JD MacDougall, Cellular Hypertrophy and Hyperplasia. In: Strength and power in sport, 2nd ed. Paavo V. Komi (ed), Malden, MA: Blackwell Science, 2003, pp 252-264
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Motor Control Section 1: The Stretch Shortening Cycle (a.k.a. plyometric movements) Unit 4: Motor Units “Net increases in fibre numbers do not occur in health adult human muscle in response to resistance exercise; or, if they do, that they are of little numerical significance.” Effects Of Genes On Structure, Function, And Performance CHARACTERISTIC EFFECT OF GENES POTENTIAL EFFECT OF TRAINING (i.e. typical environmental influences) Height, Length of Arms Large Small Muscle Fiber Composition (Fast- and Slow-Twitch) Large Small Mitochondria/Gram of Muscle Small Large Muscle Size Large Small Aerobic Endurance (e.g., distance running or cycling) # Moderate to Large Small to Moderate # Aerobic endurance is influenced by multiple organ systems, the function of some of which are largely determined by genes. So a large training effect on muscle enzymes does not mean a large effect of training on aerobic endurance.
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