Precise quantification of human motor performance is essential for effective rehabilitation and sports training. Among various aspects of motor performance, stability is one of the most important factors. Stability of rhythmic motor tasks including walking has been frequently assessed by the Floquet multipliers which were obtained from conventional regression. My presentation clarifies a critical, but hitherto neglected problem of current stability analyses of human movements; I identify a substantial bias in the stability measure and devise an improved method that can estimate stability with an order-of-magnitude fewer cycles compared with previous methods.
My presentation additionally disputes a blindly accepted common belief that chaotic system is essential to execute healthy movements. Similar to the fractal-like behaviors observed in brain and heart activity, long-range correlations in walking have commonly been interpreted to result from chaotic dynamics and be a signature of health. I show that a simple model without a system capable of chaos can reproduce the long-range correlations observed in healthy walking. My results suggest that the long-range correlation may result from a combination of noise that is ubiquitous in biological systems and orbital stability that is essential in general rhythmic movements.
Jooeun Ahn earned B.S degree from Seoul National University with summa cum laude honor in 2001. As an engineering designer and researcher in Hyundai Heavy Industries, he participated in development of an AEGIS destroyer for Republic of Korea Navy from 2001 to 2004. He received M.S. and Ph.D from MIT in 2006 and 2011 respectively. He performed research on human movement and rehabilitation robotics as a post-doctoral associate at MIT and Northeastern University. He joined the University of Victoria as an assistant professor from 2014 to 2016. He is currently an assistant professor at Seoul National University. His research interest includes dynamics of human motion, sports engineering, human motor control and nonlinear dynamics.