Subject-specific muscle synergies in human balance control are consistent across different biomechanical contexts.

@article{TorresOviedo2010SubjectspecificMS,
  title={Subject-specific muscle synergies in human balance control are consistent across different biomechanical contexts.},
  author={Gelsy Torres-Oviedo and Lena H. Ting},
  journal={Journal of neurophysiology},
  year={2010},
  volume={103 6},
  pages={
          3084-98
        }
}
The musculoskeletal redundancy of the body provides multiple solutions for performing motor tasks. We have proposed that the nervous system solves this unconstrained problem through the recruitment of motor modules or functional muscle synergies that map motor intention to action. Consistent with this hypothesis, we showed that trial-by-trial variations in muscle activation for multidirectional balance control in humans were constrained by a small set of muscle synergies. However, apparent… 

Figures from this paper

Alteration of muscle synergy structure while walking under increased postural constraints
TLDR
Lower leg muscles revealed higher activation compared to slacklining to support a more consistent toe-off during the stance phase and the modulation of synergies suggests adaptive neuromuscular strategies for stability while walking on a slackline.
Voluntary and Reactive Recruitment of Locomotor Muscle Synergies during Perturbed Walking
TLDR
This work suggests that muscle synergies may provide a library of motor subtasks that can be flexibly recruited by parallel descending pathways to generate a variety of complex natural movements in the upper and lower limbs.
Muscle Synergies are Robust across Participants in Upper Limb Rotational Motion
TLDR
It is concluded that during a constrained rotational motion at constant speed and constant power level, the muscle synergies were preserved across participants and would be useful in designing assistive devices for rehabilitation purposes.
Suboptimal Muscle Synergy Activation Patterns Generalize their Motor Function across Postures
TLDR
It is concluded that generalization of function across postures does not arise from limb biomechanics or a single optimality criterion, and Muscle synergies may reflect acquired motor solutions globally tuned for generalizability across biomechanical contexts, facilitating rapid motor adaptation.
Between-subject variability of muscle synergies during a complex motor skill
TLDR
Although variability was found (especially for synergy #3), the gymnasts exhibited gross similar neuromuscular strategies when performing backward giant swings, confirming that the muscle synergies are consistent across participants, even during a skilled motor task that requires learning.
Common muscle synergies for balance and walking
TLDR
Muscle synergies specifying spatial organization of muscle activation patterns may define a repertoire of biomechanical subtasks available to different neural circuits governing walking and reactive balance and may be recruited based on task-level goals.
Identification of shoulder muscle synergies in healthy subjects during an isometric task
TLDR
This study targets healthy subjects to establish normative data in isometric tasks involving shoulder muscles and finds the presence of subject-specific synergies which will require further investigation before examining impaired subjects.
Modularity speeds up motor learning by overcoming mechanical bias in musculoskeletal geometry
TLDR
A simple neural network model of the motor control system that included three intermediate layers representing neurons in the primary motor cortex, spinal interneurons organized into modules and motoneurons controlling upper-arm muscles demonstrated that the modules reduced the effect of the bias in the distribution of muscle pulling directions, which led to a more rapid adaptation to multi-directional force generation.
Neuromuscular organisation and robustness of postural control in the presence of perturbations
TLDR
Although a simple organisation of the neuromuscular system was sufficient to maintain the postural control in both conditions, the increased challenge in the oscillating platform was solved by adding one extra synergy, highlighting an increased motor output’s robustness in the presence of perturbations.
Review and perspective: neuromechanical considerations for predicting muscle activation patterns for movement
TLDR
It is hypothesized that subject‐specific and trial‐by‐trial differences in muscle activation can be parameterized and understood by a hierarchical and low‐dimensional framework that reflects the neural control of task‐level goals.
...
...

References

SHOWING 1-10 OF 78 REFERENCES
Muscle synergies characterizing human postural responses.
TLDR
The results suggest that muscle synergies represent a general neural strategy underlying muscle coordination in postural tasks that represents variations in the amplitude of descending neural commands that activate individual Muscle synergies.
Muscle synergy organization is robust across a variety of postural perturbations.
TLDR
The robustness of synergy organization across perturbation types, postures, and animals suggests that muscle synergies controlling task-variables are a general construct used by the CNS for balance control.
Functional muscle synergies constrain force production during postural tasks.
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.
Merging of healthy motor modules predicts reduced locomotor performance and muscle coordination complexity post-stroke.
TLDR
A common modular organization of muscle coordination underlying walking in both healthy and post-stroke subjects is suggested, which may lead to new insight into impaired locomotor coordination and the underlying neural systems.
Modulation of Muscle Synergy Recruitment in Primate Grasping
TLDR
The synergies were well conserved between monkeys, with two of the synergies exceeding chance structural similarity, and the third being recruited, in both animals, in proportion to the size of the object handled.
Modular control of human walking: a simulation study.
Stability of muscle synergies for voluntary actions after cortical stroke in humans
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.
EMG responses to maintain stance during multidirectional surface translations.
TLDR
A flexible continuum of muscle synergies that are modifiable in a task-dependent manner be used for equilibrium control in stance, consistent with a centrally mediated pattern of muscle latencies combined with peripheral influence on muscle magnitude.
...
...