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Session: Motor Control I
Session starts: Friday 25 January, 10:30
Presentation starts: 10:45
Room: Lecture room 558

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Jantsje Pasma (Department of Rehabilitation Medicine, Leiden University Medical Center, Leiden, The Netherlands)
Denise Engelhart (Laboratory of Biomechanical Engineering, MIRA, University of Twente, Enschede, The Netherlands)
Alfred Schouten (Department of Biomechanical Engineering, Delft University of Technology, Delft, The Netherlands)
Andrea Maier (Section of Gerontology and Geriatrics, Department of Internal Medicine, VU University Medical Center, Amsterdam, The Netherlands)
Carel Meskers (Department of Rehabilitation Medicine, Leiden University Medical Center, Leiden, The Netherlands)
Herman van der Kooij (Laboratory of Biomechanical Engineering, MIRA, University of Twente, Enschede, The Netherlands)

Abstract:
Sensory (re)weighting is the automated and unconscious process of dynamically combining sensory inputs, e.g. proprioception, graviception and vision, during balance control [1]. Typically, reliable sensory inputs are weighted more than unreliable and noisy sensory inputs, to prevent deterioration of balance control. Malfunctioning of sensory reweighting may be an important determinant of balance deficits in elderly with the consequence of physical impairment and falls. In this study, we compared sensory weight and reweighting of proprioceptive input of the ankle in healthy young versus healthy old adults during upright stance. Ten healthy young (aged 20-30 years) and ten healthy old adults (aged 75-80 years) were asked to maintain balance while proprioceptive input of each ankle was perturbed by rotation of the support surface around the ankle axes. Support surface rotations were applied with specific frequency content and perturbation amplitude increased over trials. Body sway and reactive ankle torque were recorded. The sensitivity function of the ankle torque to the perturbation amplitude was determined using system identification techniques [2]. The gain of the sensitivity function describes the ratio of perturbation amplitude and response amplitude as function of frequency. Parameters describing the sensitivity functions were estimated using optimized model fits. Old adults had a significant higher gain of the sensitivity function compared with young (p<0.001). Both groups showed a decrease in gain with increasing perturbation amplitude (p<0.001). The estimated proprioceptive weight was significantly higher in old adults compared with young (p<0.001). In both groups, the proprioceptive weight decreased with increasing perturbation amplitude (p<0.001). There was an interaction effect (p=0.038) between perturbation amplitude and age group. Results indicate that old and young adults had an equal capability to sensory reweight proprioceptive input during balance control, in which old adults rely more strongly on propriceptive input. These results are important in understanding the interplay between available sensory inputs in balance and falling.