Short‐term high‐ vs low‐velocity isokinetic lengthening training results in greater hypertrophy of the elbow flexors in young men

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).