Kai Lon Fok1, Jae Lee2, Albert H Vette3, Kei Masani4. 1. Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario M5S 3G9, Canada. 2. Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario M5S 3G9, Canada; Lyndhurst Centre, Toronto Rehabilitation Institute - University Health Network, 520 Sutherland Drive, Toronto, Ontario M4G 3V9, Canada. 3. Department of Mechanical Engineering, University of Alberta, 10-203 Donadeo Innovation Centre for Engineering, 9211 116 Street NW, Edmonton, Alberta T6G 1H9, Canada; Glenrose Rehabilitation Hospital, Alberta Health Services, 10230 111 Avenue NW, Edmonton, Alberta T5G 0B7, Canada. 4. Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario M5S 3G9, Canada; Lyndhurst Centre, Toronto Rehabilitation Institute - University Health Network, 520 Sutherland Drive, Toronto, Ontario M4G 3V9, Canada. Electronic address: k.masani@utoronto.ca.
Abstract
BACKGROUND: Many postural control studies employ a single-mass inverted pendulum model (IPM) to represent the body during standing. However, it is not known to what degree and for what conditions the model's kinematic assumptions are valid. RESEARCH QUESTION: Our first objective was to quantify the IPM error, corresponding to a distance change between the ankle joint and center of mass (COM) during unrestricted, natural, unperturbed standing. A second objective was to quantify the error of having the ankle joint angle represent the COM angle. METHODS: Eleven young participants completed five standing conditions: quiet standing with eyes open (EO) and closed (EC), voluntarily swaying forward (VSf) and backward (VSb), and freely moving (FR). The modified Helen-Hayes marker model was used to capture the body kinematics. RESULTS: The COM distance changed <0.1% during EO and EC, <0.25% during VSf and VSb, and <1.5% during FR. The ankle angle moderately and positively correlated with the COM angle for EO, EC, and VSf, indicating that temporal features of the ankle angle moderately represent those of the COM angle. However, a considerable offset between the two existed, which needs to be considered when estimating the COM angle using the ankle angle. For VSb and FR, the correlation coefficients were low and/or negative, suggesting that a large error would result from using the ankle angle as an estimate of the COM angle. SIGNIFICANCE: Insights from this study will be critical for deciding when to use the IPM in postural control research and for interpreting associated results.
BACKGROUND: Many postural control studies employ a single-mass inverted pendulum model (IPM) to represent the body during standing. However, it is not known to what degree and for what conditions the model's kinematic assumptions are valid. RESEARCH QUESTION: Our first objective was to quantify the IPM error, corresponding to a distance change between the ankle joint and center of mass (COM) during unrestricted, natural, unperturbed standing. A second objective was to quantify the error of having the ankle joint angle represent the COM angle. METHODS: Eleven young participants completed five standing conditions: quiet standing with eyes open (EO) and closed (EC), voluntarily swaying forward (VSf) and backward (VSb), and freely moving (FR). The modified Helen-Hayes marker model was used to capture the body kinematics. RESULTS: The COM distance changed <0.1% during EO and EC, <0.25% during VSf and VSb, and <1.5% during FR. The ankle angle moderately and positively correlated with the COM angle for EO, EC, and VSf, indicating that temporal features of the ankle angle moderately represent those of the COM angle. However, a considerable offset between the two existed, which needs to be considered when estimating the COM angle using the ankle angle. For VSb and FR, the correlation coefficients were low and/or negative, suggesting that a large error would result from using the ankle angle as an estimate of the COM angle. SIGNIFICANCE: Insights from this study will be critical for deciding when to use the IPM in postural control research and for interpreting associated results.
Authors: David F Rusaw; Rasmus Alinder; Sigurd Edholm; Karin L L Hallstedt; Jessika Runesson; Cleveland T Barnett Journal: Sci Rep Date: 2021-04-15 Impact factor: 4.379