so does rep speed matter when concerned about muscle strength, hypertrophy, and damage?

should we emphasize concentric or eccentric contractions?

well shepstone et al. (2005) examined the effects of rep speed on muscle hypertrophy using multiple outcomes. "fast" and "slow" lengthening (eccentric contractions) of biceps brachii were used to observe changes in strength, cross sectional area, specific muscle fibers, and mixed muscle myo. muscle biopsies of the biceps were taken pre and post training.

type i fiber increased for both fast and slow speeds.
type iia and iix fibers increased for both speeds but, increases in cross sectional area were significantly increased for fast speeds.

strength increased regardless of velocity but larger strength was measured for fast eccentric contractions.

also, protein remodeling was examined to understand the greater hypertrophy in eccentric fast contractions. z band disruption was signficantly greater for fast reps. z band disruption is an indicator of muscle "damage" and fiber remodeling.

of course this is what we want to hear when training. greater protein synthesis would result in greater muscle hypertrophy.

ok, the take-to-the-gym message is:
use eccentric contractions with heavy loads for strength and hypertrophy,
vary rep speed to include decreased time under tension (e.g., ~2-3 sec) during eccentrics.

do you guys get better results with varying rep speed and emphasizing eccentrics?

Short-term high- vs. low-velocity isokinetic lengthening training results in greater hypertrophy of the elbow flexors in young men
Tim N. Shepstone,1 Jason E. Tang,1 Stephane Dallaire,1 Mark D. Schuenke,2 Robert S. Staron,2 and Stuart M. Phillips1

1Exercise and Metabolism Research Group, Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada; and 2Department of Biomedical Sciences, College of Osteopathic Medicine, Ohio University, Athens, Ohio
Submitted 16 September 2004 ; accepted in final form 29 December 2004
We performed two studies to determine the effect of a resistive training program comprised of fast vs. slow isokinetic lengthening contractions on muscle fiber hypertrophy. In study I, we investigated the effect of fast (3.66 rad/s; Fast) or slow (0.35 rad/s; Slow) isokinetic high-resistance muscle lengthening contractions on muscle fiber and whole muscle cross-sectional area (CSA) of the elbow flexors was investigated in young men. Twelve subjects (23.8 ± 2.4 yr; means ± SD) performed maximal resistive lengthening isokinetic exercise with both arms for 8 wk (3 days/wk), during which they trained one arm at a Fast velocity while the contralateral arm performed an equivalent number of contractions at a Slow velocity. Before (Pre) and after (Post) the training, percutaneous muscle biopsies were taken from the midbelly of the biceps brachii and analyzed for fiber type and CSA. Type I muscle fiber size increased Pre to Post (P < 0.05) in both Fast and Slow arms. Type IIa and IIx muscle fiber CSA increased in both arms, but the increases were greater in the Fast- vs. the Slow-trained arm (P < 0.05). Elbow flexor CSA increased in Fast and Slow arms, with the increase in the Fast arm showing a trend toward being greater (P = 0.06). Maximum torque-generating capacity also increased to a greater degree (P < 0.05) in the Fast arm, regardless of testing velocity. In study II, we attempted to provide some explanation of the greater hypertrophy observed in study I by examining an indicator of protein remodeling (Z-line streaming), which we hypothesized would be greater in the Fast condition. Nine men (21.7 ± 2.4 yr) performed an acute bout (n = 30, 3 sets x 10 repetitions/set) of maximal lengthening contractions at Fast and Slow velocities used in the training study. Biopsies revealed that Fast lengthening contractions resulted in more (185 ± 1 7%; P < 0.01) Z-band streaming per millimeter squared muscle vs. the Slow arm. In conclusion, training using Fast (3.66 rad/s) lengthening contractions leads to greater hypertrophy and strength gains than Slow (0.35 rad/s) lengthening contractions. The greater hypertrophy seen in the Fast-trained arm (study I) may be related to a greater amount of protein remodeling (Z-band streaming; study II).
muscle damage; time under tension; Z-band disruption

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