Similar increases in muscle size and strength in young men after training with maximal shortening or lengthening contractions when matched for total work

Training exclusively with eccentric (lengthening) contractions can result in greater muscular adaptations than training with concentric (shortening) contractions. We aimed to determine whether training-induced increases in muscle size and strength differed between muscles performing maximal lengthening (LC) or maximal shortening (SC) contractions when total external work is equivalent. Nine healthy young males completed a 9-week isokinetic (0.79 rad/s) resistance training program of the elbow flexors whereby they performed LC with one arm and an equivalent volume of total external work with the contralateral arm as SC. Training increased isometric peak torque for both LC (similar to 10%) and SC (similar to 20%) with no difference (P = 0.14) between conditions. There were also similar increases in isokinetic peak torque at both slow (0.79 rad/s) and fast (5.24 rad/s) shortening and lengthening peak torque for both LC (similar to 8-10%) and SC (similar to 9-20%). Training increased work per repetition similarly for both LC (similar to 17%) and SC (similar to 22%), in spite of similar to 40% greater work per repetition with LC. The increase in muscle cross-sectional area with training was also similar (P = 0.37) between LC (similar to 6.5%) and SC (similar to 4.6%). We conclude that increases in muscle size and strength with short-term unilateral resistance training are unrelated to muscle contraction type when matched for both exercise intensity (i.e. maximal contractions) and total external work.