The present study aimed to examine the effect of short-term training utilizing voluntary co-contraction with maximal efforts. 23 healthy young men (training group: TG, n = 13; control group: CG, n = 10) participated in this study. TG conducted a 4-week training program (3 days/week), which consisted of 4 s simultaneous maximal voluntary contractions of elbow flexors and extensors at 90° of the elbow joint, followed by 4 s muscle relaxation (10 repetitions/set, 5 sets/day). Before and after the intervention, maximal voluntary isometric and isokinetic torques and the muscle thicknesses of the elbow flexors and extensors were determined. The electromyograms (EMGs) of the 2 muscle groups during isometric maximal voluntary contraction (MVC) were also recorded. After the intervention, CG did not show any significant changes in all measured variables. In TG, significant increases were found in the agonist EMG activities during MVC, and maximal isometric and isokinetic torques of the elbow flexors and extensors, without significant changes in the muscle thicknesses and involuntary coactivation levels during MVC. The current results indicate that the training mode with maximal voluntary co-contraction is effective for improving the force-generating capabilities of the exercising muscles, without any increases in the level of involuntary coactivation during MVC.
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