Transfer Mechanisms of Eccentric Training : The effects of EMG-biofeedback in training

Abstract Aim: The aim of this study was to investigate how neural mechanisms operate during maximum strength training in the Quadriceps Femoris muscle group. One of the main objectives is to investigate the effects of five weeks unilateral maximum eccentric strength training on contralateral neural adaptations. The second is to investigate the effects of adding electromyographic (EMG) biofeedback into the training intervention. Method: 20 healthy, recreationally active men and women had to undergo five weeks (three training sessions per week, resulting in 15 sessions in total) of maximum isokinetic unilateral eccentric strength training of the Quadriceps femoris muscle, with EMG biofeedback; FBG, n=10 five women and five men, or without EMG biofeedback; RTG n=10 five women and five men. The study was performed at the Laboratory of Biomechanics and Motor control, BMC Laboratory, Stockholm Sweden. Results: The results demonstrated an increase in concentric strength development in the trained leg; before 130 ± 43 Nm and after training 148 ± 46 Nm, (p=0.006). No significant increase in strength was detected for the untrained leg. Further, post hoc tests showed a tendency towards an increase in level of activation (LOA) of the trained leg in the FBG; from 69 ± 15 % before to 81 ± 13 % after training (p=0.097). No significant differences in the ecc:con EMG-ratio or in antagonist co-activation after the training intervention were shown. Conclusion: No significant difference in strength development was shown, whether training occurred with or without EMG biofeedback. However, eccentric training tended to induce transfer of neural activation to a maximum voluntary contraction (MVC) in the trained leg only in the group training with EMG biofeedback. In addition, the results revealed that eccentric strength training improved concentric strength in the trained leg but induced no transfer to the contralateral untrained leg. The benefits and prospects with incorporating feedback into training remains somewhat unknown and requires further research to obtain deeper understanding of the neural mechanisms affected by biofeedback