Maeo, S., Yoshitake, Y., Takai, Y., Fukunaga, T., & Kanehisa, H. (2012). Effects of resistance training with maximal voluntary co-contraction on neuromuscular function. Presentation 1873 at the 59th Annual Meeting of the American College of Sports Medicine, San Francisco, California; May 29-June 2, 2012.

Simultaneous contractions of antagonistic muscles (co-contraction) produce resistive forces which act against each other. It was hypothesized that a training mode with maximal voluntary co-contraction would be a novel form for improving the strength capability of the muscles within antagonistic pairs without any apparatuses or external loads. This study examined neuromuscular adaptations following maximal voluntary co-contraction training in healthy young men (N = 16). Ss were divided into a training group (N = 9) and a control group (N = 7). The training group performed a 12-week program (3 days per week) for elbow flexors and extensors. The exercises consisted of a 4-second maximal co-contraction of the flexors and extensors at 90° of the elbow joint, followed by a 4-second muscle relaxation (10 repetitions in a set, 5 sets per day). The torque during isometric maximal voluntary contraction during maximal voluntary contraction of each of the muscle groups, their electromyographic activity during maximal voluntary contraction and maximal co-contraction, and the muscles' thickness (by ultrasound) were determined before, at the ends of 4 weeks, and at the end of 12 weeks of the intervention.

The EMG activities of the flexors and extensors during maximal co-contraction, expressed relative to those during the maximal voluntary contraction of the corresponding muscle group, were 43% and 60%, respectively. [Those were the percentage of the contraction in dual activity compared to contractile activity when working the muscles alone.] They were unchanged through the intervention period. The control group did not show any significant changes in any variables. For the training group, maximal voluntary contraction torque was significantly increased in the flexors (+12.5% at week 4; +15.4% at week 12) and extensors (+27.4% at week 4; +46.0% at week 12) when compared to values obtained before the intervention. Muscle thickness for training group was also significantly increased in both muscle groups (+1.2 mm) at week 12. As well, the training group showed significant gains in agonist EMG activities during maximal voluntary contraction in both the flexors (+31.1% at week 4; +44.0% at week 12) and extensors (+27.3% at week 4; +39.8% at week 12), without change in antagonist involuntary co-activation level in each of the two muscle groups.

Implication. Maximal voluntary co-contraction can be a resistance modality which increases the strength capability of both of the antagonistic muscles, without any increases in involuntary co-activation level during maximal voluntary contraction. At least for light load sports (e.g., swimming, running, kayaking, baseball pitching) this form of muscle development could very well be a substitute for the more limited injury-threatening weight-room activities.

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