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.