Sequential activation of muscle synergies during locomotion in the intact cat as revealed by cluster analysis and direct decomposition.

@article{Krouchev2006SequentialAO,
  title={Sequential activation of muscle synergies during locomotion in the intact cat as revealed by cluster analysis and direct decomposition.},
  author={Nedialko I. Krouchev and John F. Kalaska and Trevor Drew},
  journal={Journal of neurophysiology},
  year={2006},
  volume={96 4},
  pages={
          1991-2010
        }
}
During goal-directed locomotion, descending signals from supraspinal structures act through spinal interneuron pathways to effect modifications of muscle activity that are appropriate to the task requirements. Recent studies using decomposition methods suggest that this control might be facilitated by activating synergies organized at the level of the spinal cord. However, it is difficult to directly relate these mathematically defined synergies to the patterns of electromyographic activity… 
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Muscle synergies during locomotion in the cat: a model for motor cortex control
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Results demonstrate that by modifying the phase and magnitude of a finite number of muscle synergies, each comprised of a small number of simultaneously active muscles, descending control signals could produce very specific modifications in limb trajectory during locomotion.
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TLDR
The notion that descending cortical signals represent neuronal drives that select, activate, and flexibly combine muscle synergies specified by networks in the spinal cord and/or brainstem is supported.
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TLDR
It is suggested that during locomotion the activity in interneuronal pathways mediating signals from the reticulospinal system is subject to strong modulation by the central pattern generator for locomotion.
Direction Modulation of Muscle Synergies in a Hand-Reaching Task
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Muscle synergies that were extracted from movements to the center of the reaching space could be generalized to synergies for other movement directions, and might reinforce the notion that the CNS flexibly combines a single set of small number of synergies in different amplitudes to modulate movement for different directions.
Adjustments of motor pattern for load compensation via modulated activations of muscle synergies during natural behaviors.
TLDR
Investigating whether motor responses observed after an inertial-load perturbation can be generated by altering the recruitment of synergies normally used for constructing unperturbed movements suggests that muscle synergies are robust across different dynamic conditions and immediate motor adjustments can be accomplished by modulating synergy activations.
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