09.23.2009 - Young-Hui Chang - Neuromechanics of hopping
Papers
- Boscow & Poppoli 2000
- Chang, Roiz & Auyang, J Biomech 2008
- Yen & Chang, Exp Brain Res 2009
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.