According to the article "Trainability of Muscular Activity Level during Maximal Voluntary Co-Contraction: Comparison between Bodybuilders and Nonathletes," antagonistic muscle pairs cannot be fully activated simultaneously, even with maximal effort, under conditions of voluntary co-contraction, and their muscular activity levels are always below those during agonist contraction with maximal voluntary effort (MVE).

This figure demonstrates relationship between bodybuilding experience and muscular activity level during maximal voluntary co-contraction task. We can see that max voluntary biceps/triceps co-contraction is ~60-80% of maximal tension. Significant positive correlation was found between a length of bodybuilding experience and % EMG/MVE (averaged over biceps and triceps brachii muscles) during maximal voluntary co-contraction task. doi:10.1371/journal.pone.0079486.g003

This figure also shows that co-contraction-based training could be considered as a skill-based workout, and that the improvement of the mind-body connection increases the efficiency of co-contraction. More important, the figure clearly demonstrates that co-contraction skill, leading to progressive muscle loading (co-contraction), growths slow. Thus, we could expect that strength gaining will be slower during co-contraction training compared to weightlifting, and that high volume performance could be "a main player" to get muscle hypertrophy.