title: Measuring multi-joint stiffness during single movements: numerical validation of a novel time-frequency approach.
abstract: This study presents and validates a Time-Frequency technique for measuring 2-dimensional multijoint arm stiffness throughout a single planar movement as well as during static posture. It is proposed as an alternative to current regressive methods which require numerous repetitions to obtain average stiffness on a small segment of the hand trajectory. The method is based on the analysis of the reassigned spectrogram of the arm's response to impulsive perturbations and can estimate arm stiffness on a trial-by-trial basis. Analytic and empirical methods are first derived and tested through modal analysis on synthetic data. The technique's accuracy and robustness are assessed by modeling the estimation of stiffness time profiles changing at different rates and affected by different noise levels. Our method obtains results comparable with two well-known regressive techniques. We also test how the technique can identify the viscoelastic component of non-linear and higher than second order systems with a non-parametrical approach. The technique proposed here is very impervious to noise and can be used easily for both postural and movement tasks. Estimations of stiffness profiles are possible with only one perturbation, making our method a useful tool for estimating limb stiffness during motor learning and adaptation tasks, and for understanding the modulation of stiffness in individuals with neurodegenerative diseases.
authors.affiliation: Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois, United States of America. d-piovesan@northwestern.edu
authors.forename: Davide
authors.initials: D
authors.lastname: Piovesan
authors.forename: Alberto
authors.initials: A
authors.lastname: Pierobon
authors.forename: Paul
authors.initials: P
authors.lastname: DiZio
authors.forename: James R
authors.initials: JR
authors.lastname: Lackner
mesh_terms: D000465:Algorithms; D001132:Arm / Q000502:physiology*; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D004548:Elasticity; D006801:Humans; D007596:Joints / Q000502:physiology*; D008954:Models, Biological; D009043:Motor Activity / Q000502:physiology*; D012044:Regression Analysis; D013997:Time Factors