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1 Department of Kinesiology, Exercise and Metabolism Research Group, McMaster University, Hamilton, ON, Canada
2 Department of Biomedical Sciences, College of Osteopathic Medicine, Ohio University, Athens, OH, USA
* To whom correspondence should be addressed. E-mail: phillis{at}mcmaster.ca.
Study I - The effect of fast (3.66 rad/s, FAST) or slow (0.35 rad/s, SLOW) 1 isokinetic high-resistance muscle lengthening contractions on muscle fiber and whole muscle 2 cross-sectional area (CSA) of the elbow flexors was investigated in young men. Twelve subjects 3 (23.8±2.4yr, mean±SD) performed maximal resistive lengthening isokinetic exercise with both 4 arms for 8wk (3d/wk), during which they trained one arm at a FAST velocity while the 5 contralateral arm performed an equivalent number of contractions at a SLOW velocity. Before 6 (PRE) and after (POST) the training, percutaneous muscle biopsies were taken from the mid 7 belly of the biceps brachii and analyzed for fiber type and CSA. Type I muscle fiber size 8 increased PRE to POST (P<0.05) in both FAST and SLOW arms. Type IIa and IIx muscle fiber 9 CSA increased in both arms, but the increases were greater in the FAST versus the SLOW 10 trained arm (P<0.05). Elbow flexor CSA increased in FAST and SLOW arms, with the increase 11 in the FAST arm showing a trend towards being greater (P=0.06). Maximum torque generating 12 capacity also increased to a greater degree (P<0.05) in the FAST arm, regardless of testing 13 velocity. Study II - In a separate study, we attempted to provide some explanation of the greater 14 hypertrophy observed in study I by examining an indicator of protein remodeling (Z-line 15 streaming), which we hypothesized would be greater in the FAST condition. Nine men 16 (21.7±2.4yr) performed an acute bout (N=30, 3 sets x 10 repetitions/set) of maximal lengthening 17 contractions at FAST and SLOW velocities used in the training study. Biopsies revealed that 18 FAST lengthening contractions resulted in more (185±17%; P<0.01) Z-band streaming/mm2 19 muscle, versus the SLOW arm. In conclusion, training using FAST (3.66 rad/s) lengthening 20 contractions leads to greater hypertrophy and strength gains than SLOW (0.35 rad/s) lengthening 21 contractions. The greater hypertrophy seen in the FAST trained arm (study I) may be related to a 22 greater amount of protein remodelling (Z-band streaming; study II).
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