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Shepstone, T N.1; Dallaire, S A.1; Correia, C E.1; Tang, J E.1; Phillips, S M.1

Medicine & Science in Sports & Exercise: May 2003 - Volume 35 - Issue 5 - p S386
H-13P Free Communication/Poster Skeletal Muscle Physiology

1McMaster University, Hamilton, ON

Eccentric as opposed to concentric muscle actions recruit less motor units for a given load, which places a greater stress (i.e., force per active motor unit) on the muscle, resulting in greater muscle damage. Increasing the velocity of eccentric muscle actions also generates higher muscle forces, to a point, after which force plateaus. Performing eccentric actions at a higher velocity may maximize muscle stress, result in greater muscle damage and generate a greater stimulus for hypertrophy, versus slower eccentric actions.

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We wished to determine if the velocity of isokinetic eccentric muscle actions - FAST (3.66 rad/s) versus SLOW (0.35 rad/s) - had an impact on the degree of fibre hypertrophy of the elbow flexors during an 8 wk high-resistance training program.

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Young males (N=9, 25±5 yrs; means±SE) had their arms randomly assigned to be resistance trained (3d/wk × 8 wk; elbow flexion) on an isokinetic dynamometer at a FAST eccentric velocity, while their contralateral arm was trained using a SLOW velocity. Changes in the cross-sectional area (CSA) of muscle fibres were evaluated from muscle biopsy samples taken from both elbow flexors pre-training and post-training. Biopsies were stained using traditional ATPase histochemistry and analyzed using image analysis software.

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Type I fibres showed significant hypertophy as a result of the protocol, but there was no difference between FAST and SLOW. Type II muscle fibre (IIx, IIa/x, IIa) CSA was increased as a result of the protocol, but the increase was significantly greater in the elbow flexors that performed FAST eccentric actions versus SLOW. For type IIx, IIa/x, and IIa fibres respectively: FAST: +31±5, +22±5 and +17±5 vs. SLOW: +9±5, +10±3 and +5±2\%, all p < 0.05.

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A FAST eccentric contraction velocity, 10-fold greater than the corresponding SLOW eccentric velocity, produced a greater hypertrophic gain in elbow flexor fast twitch fibre CSA following 8 wk of isokinetic high-resistance training in young men. Supported by NSERC.

©2003The American College of Sports Medicine