Abstract Changes in muscle activation and performance were studied in healthy men in response to 5 weeks of resistance training with or without “eccentric overload”. Subjects, assigned to either weight stack (grp WS; n = 8) or iso-inertial “eccentric overload” Xywheel (grp FW; n = 9) knee extensor resistance training, completed 12 sessions of four sets of seven concentric–eccentric actions. Pre- and post-measurements comprised maximal voluntary contrac- tion (MVC), rate of force development (RFD) and training mode-speciWc force. Root mean square electromyographic (EMGRMS) activity of mm. vastus lateralis and medialis was assessed during MVC and used to normalize EMGRMS for training mode-speciWc concentric (EMGCON) and eccentric (EMGECC) actions at 90°, 120° and 150° knee joint angles. Grp FW showed greater (p < 0.05) overall normalized angle-speciWc EMGECC of vastii muscles compared with grp WS. Grp FW showed near maximal normalized EMGCON both pre- and post-training. EMGCON for Grp WS was near maximal only post-training. While RFD was unchanged following training (p > 0.05), MVC and training-specific strength increased (p < 0.05) in both groups.We believe the higher EMGECC activity noted with FW exercise compared to standard weight lifting could be attributed to its unique iso-inertial loading features. Hence, the resulting greater mechanical stress may explain the robust muscle hypertrophy reported earlier in response to Xywheel resistance training.
Keywords Concentric and eccentric actions · Electromyography · Iso-inertia · Resistance exercise