Biological Cybernetics

, Volume 93, Issue 5, pp 373–381 | Cite as

Can co-activation reduce kinematic variability? A simulation study

  • Luc P. J. Selen
  • Peter J. Beek
  • Jaap H. van Dieën
Original Paper


Impedance modulation has been suggested as a means to suppress the effects of internal ‘noise’ on movement kinematics. We investigated this hypothesis in a neuro-musculo-skeletal model. A prerequisite is that the muscle model produces realistic force variability. We found that standard Hill-type models do not predict realistic force variability in response to variability in stimulation. In contrast, a combined motor-unit pool model and a pool of parallel Hill-type motor units did produce realistic force variability as a function of target force, largely independent of how the force was transduced to the tendon. To test the main hypothesis, two versions of the latter model were simulated as an antagonistic muscle pair, controlling the position of a frictionless hinge joint, with a distal segment having realistic inertia relative to the muscle strength. Increasing the impedance through co-activation resulted in less kinematic variability, except for the lowest levels of co-activation. Model behavior in this region was affected by the noise amplitude and the inertial properties of the model. Our simulations support the idea that muscular co-activation is in principle an effective strategy to meet accuracy demands.


Motor Unit Interspike Interval Force Variability Impedance Modulation Series Elastic Element 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  • Luc P. J. Selen
    • 1
  • Peter J. Beek
    • 1
  • Jaap H. van Dieën
    • 1
  1. 1.Faculty of Human Movement Sciences and Institute for Fundamental and Clinical Human Movement SciencesVrije UniversiteitAmsterdamThe Netherlands

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