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Evidence for a time-invariant phase variable in human ankle control.

Robert D Gregg1, Elliott J Rouse2, Levi J Hargrove3

  • 1Departments of Mechanical Engineering and Bioengineering, University of Texas at Dallas, Richardson, Texas, United States of America.

Plos One
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Summary

Human locomotion may use a simple biomechanical phase variable, like foot pressure movement, to control gait. This finding suggests a new way to understand how the body generates rhythmic movements and adapts to changes.

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Area of Science:

  • Biomechanics
  • Neuroscience
  • Robotics

Background:

  • Human locomotion involves complex muscle activity modulated by feedback.
  • Current theories on gait phase control include time-dependent or feedback representations.
  • Legged robots utilize simpler phase variables for joint pattern control.

Purpose of the Study:

  • To investigate if human joint patterns depend on a physical phase variable.
  • To explore the role of the Center of Pressure (CoP) as a potential phase variable in human locomotion.

Main Methods:

  • Ankle rotation perturbation during human walking.
  • Measurement of Center of Pressure (CoP) shifts.
  • Observation of subsequent gait pattern adjustments.

Main Results:

  • Unexpected ankle rotation caused a forward shift in the CoP.
  • The CoP shift corresponded to a later position in the gait cycle.
  • The remainder of the gait pattern continued as if the CoP had naturally reached that position.

Conclusions:

  • The results suggest a biomechanical phase variable, specifically CoP movement, controls stance ankle progression.
  • This challenges existing models and proposes a simpler mechanism for human locomotor control.
  • Further research into phase variables for human locomotion is warranted.