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09.23.2009 - Young-Hui Chang - Neuromechanics of hopping

Papers
Limb Kinematics
  • Total limb stiffness of the leg is preserved even when joint kinematics change.
    • Additional stiffness added (1-joint strategy)
    • Resistive load added (2-joint strategy)
  • What are the magnitude of the errors in the experiments?  How does this effect the calculation of joint stiffness?
  • How does this relate to the equilibrium point hypothesis?
Injured Nerves
  • Joint kinematics show large changes in kinematics
    • Not consistent across subjects
  • Total limb "length" and "angle" are preserved
  • Timing of the limb coordination is changed, but the spatial patterns are conserved.
    • Is this because mechanics dominates the effects?
Unconstrained Manifold in Hopping
  • Examination of variance suggests that leg length is stabilized during ground contact and leg angle is stabilized during flight.
  • Variance increases with increased frequency of hopping
  • Ground reaction force variance is at a minimum when maximum power (midstance) is achieved, even when individual joint torque variance is maximum.
Joint Covariation in Hopping
  • Suggests coordinated joint control at low frequencies, little coordination at higher frequencies
Clinical Relevance
  • Gait rehabilitation - Teach people to maintain leg length instead of trying to match joint kinematics, just let the joints take care of themselves.
  • Exoskeleton - From observations it appears that neural control switches between multiple control schedules.  Do this instead of trying to reduce the task space.
    • Argument to this is that in most design scenarios robustness is the biggest issue and switching is not easily stabilizable for all scenarios.
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