In this study, we identified a low-dimensional representation of control mechanisms in throwing motions from a variety of subjects\nand target distances. The control representation was identified at the kinematic level in task and joint spaces, respectively, and at the\nmuscle activation level using the theory of muscle synergies. Representative features of throwing motions in all of these spaces were\nchosen to be investigated. Features were extracted using factorization and clustering techniques from the muscle data of\nunexperienced subjects (with different morphologies and physical conditions) during a series of throwing tasks. Two synergy\nextraction methods were tested to assess their consistency. For the task features, the degrees of freedom (DoF), and the muscles\nunder study, the results can be summarized as (1) a control representation across subjects consisting of only two synergies at the\nactivation level and of representative features in the task and joint spaces, (2) a reduction of control redundancy (since the\nnumber of synergies are less than the number of actions to be controlled), (3) links between the synergies triggering intensity\nand the throwing distance, and finally (4) consistency of the extraction methods. Such results are useful to better represent\nmechanisms hidden behind such dynamical motions and could offer a promising control representation for synthesizing\nmotions with muscle-driven characters.
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