title: Real-time estimation of intrinsic and reflex stiffness.
abstract: Joint stiffness is defined as the dynamic relationship between the position of the joint and torque acting about it. Joint stiffness is composed of two components: intrinsic and reflex stiffness. Measuring the two stiffness components cannot be done simply because the two components appear and change together. A number of approaches have been used to estimate the components, but all those approaches are inherently off-line. We have developed novel algorithm that separates and estimates the two components in real-time. Intrinsic stiffness was estimated by finding the cross-correlations between the position, its derivatives and the torque. Reflex stiffness was estimated by finding the IRF between the half-wave rectified velocity and the estimated reflex torque. A novel position perturbation, consisting of pseudo random series of pulses of different lengths, was used to eliminate covariance of intrinsic and reflex stiffness estimates. Using simulated data, the real-time estimates were shown to be estimated accurately. The real-time estimation algorithm was validated by comparing the real-time estimates with estimates generated by the parallel-cascade identification, an established off-line intrinsic and reflex stiffness identification algorithm, using simulated and experimental data. The estimates produced by the two algorithms were in agreement for both simulated and experimental data.
authors.affiliation: Dept. of Biomedical Engineering, McGill University, Montreal, QC, Canada. daniel.ludvig@mail.mcgill.ca
authors.forename: Daniel
authors.initials: D
authors.lastname: Ludvig
authors.forename: Robert E
authors.initials: RE
authors.lastname: Kearney
mesh_terms: D000465:Algorithms; D000843:Ankle Joint / Q000294:innervation / Q000502:physiology*; D002358:Cartilage, Articular / Q000294:innervation / Q000502:physiology*; D003198:Computer Simulation; D003199:Computer Systems; D004548:Elasticity; D005246:Feedback / Q000502:physiology; D006801:Humans; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D012018:Reflex / Q000502:physiology*; D013314:Stress, Mechanical