Publications by authors named "Ronald G Aarts"

2 Publications

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Reliability of System Identification Techniques to Assess Standing Balance in Healthy Elderly.

PLoS One 2016 8;11(3):e0151012. Epub 2016 Mar 8.

Department of Biomechanical Engineering, Delft University of Technology, Delft, the Netherlands.

Objectives: System identification techniques have the potential to assess the contribution of the underlying systems involved in standing balance by applying well-known disturbances. We investigated the reliability of standing balance parameters obtained with multivariate closed loop system identification techniques.

Methods: In twelve healthy elderly balance tests were performed twice a day during three days. Body sway was measured during two minutes of standing with eyes closed and the Balance test Room (BalRoom) was used to apply four disturbances simultaneously: two sensory disturbances, to the proprioceptive and the visual system, and two mechanical disturbances applied at the leg and trunk segment. Using system identification techniques, sensitivity functions of the sensory disturbances and the neuromuscular controller were estimated. Based on the generalizability theory (G theory), systematic errors and sources of variability were assessed using linear mixed models and reliability was assessed by computing indexes of dependability (ID), standard error of measurement (SEM) and minimal detectable change (MDC).

Results: A systematic error was found between the first and second trial in the sensitivity functions. No systematic error was found in the neuromuscular controller and body sway. The reliability of 15 of 25 parameters and body sway were moderate to excellent when the results of two trials on three days were averaged. To reach an excellent reliability on one day in 7 out of 25 parameters, it was predicted that at least seven trials must be averaged.

Conclusion: This study shows that system identification techniques are a promising method to assess the underlying systems involved in standing balance in elderly. However, most of the parameters do not appear to be reliable unless a large number of trials are collected across multiple days. To reach an excellent reliability in one third of the parameters, a training session for participants is needed and at least seven trials of two minutes must be performed on one day.
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August 2016

Assessment of Multi-Joint Coordination and Adaptation in Standing Balance: A Novel Device and System Identification Technique.

IEEE Trans Neural Syst Rehabil Eng 2015 Nov 20;23(6):973-82. Epub 2014 Nov 20.

The ankles and hips play an important role in maintaining standing balance and the coordination between joints adapts with task and conditions, like the disturbance magnitude and type, and changes with age. Assessment of multi-joint coordination requires the application of multiple continuous and independent disturbances and closed loop system identification techniques (CLSIT). This paper presents a novel device, the double inverted pendulum perturbator (DIPP), which can apply disturbing forces at the hip level and between the shoulder blades. In addition to the disturbances, the device can provide force fields to study adaptation of multi-joint coordination. The performance of the DIPP and a novel CLSIT was assessed by identifying a system with known mechanical properties and model simulations. A double inverted pendulum was successfully identified, while force fields were able to keep the pendulum upright. The estimated dynamics were similar as the theoretical derived dynamics. The DIPP has a sufficient bandwidth of 7 Hz to identify multi-joint coordination dynamics. An experiment with human subjects where a stabilizing force field was rendered at the hip (1500 N/m), showed that subjects adapt by lowering their control actions around the ankles. The stiffness from upper and lower segment motion to ankle torque dropped with 30% and 48%, respectively. Our methods allow to study (pathological) changes in multi-joint coordination as well as adaptive capacity to maintain standing balance.
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Source Listing
November 2015