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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).

J Appl Physiol2005 Jan: 7[Epub ahead of print]Study I– 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 years, mean±SD) performed maximal resistive lengthening isokinetic exercise with both arms for 8 weeks (3 days/week), 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 mid-belly 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. Study II– In a separate study, 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 years) performed an acute bout (N=30, 3 sets× 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±17%;P<0.01) Z-band streaming/mm(2) 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). [ABSTRACT FROM AUTHOR]