Identification of the Parameters of Double-Pendulum Intermittent Delay Feedback Control Model Using Optimization Method

The identification of the parameters of postural control models may aid evaluating the balance control mechanism. A novel approach suggests that the central nervous system adopts an intermittent active feedback control to maintain upright posture, since this strategy may explain better the spontaneous sway. The aims of this work are to analyze the intermittent strategy of subjects in different sensorial conditions and to propose a method to identify the parameters of an intermittent delay feedback control model, applied to the double-pendulum biomechanical model. Four sway parameters (mean velocity, range, signal RMS and frequency band) were calculated from signals available in a public dataset containing body sway records of young and old subjects in trials with eyes open/closed on rigid/foam surface. An intermittence parameter ρ was obtained using system identification with a genetic algorithm optimization approach. The sway parameters were significantly different between eyes open/closed on rigid/foam surface (p < 0.001); the intermittence parameter ρ suggests that the subjects use more the active control when the trial becomes more challenging (p < 10–9), and the older subjects use more the active control than younger (p < 0.01). The optimization meth-od was able to identify parameters that could reproduce sway patterns that also distinguished between trials with eyes open/closed on rigid/foam surface (velocity p = 0.00005, range p = 0.00005, RMS p = 0.00005). The evaluation of further models, incorporating a different set of parameters, search intervals and optimization criteria, may improve system identification.