Fok Kai Lon, Lee Jae, Vette Albert H, Masani Kei
Institute of Biomaterials and Biomedical Engineering, University of Toronto, 164 College Street, Toronto, Ontario M5S 3G9, Canada.
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.
Gait Posture. 2018 Jun;63:23-26. doi: 10.1016/j.gaitpost.2018.04.021. Epub 2018 Apr 18.
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.
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.
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.
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.
Insights from this study will be critical for deciding when to use the IPM in postural control research and for interpreting associated results.
许多姿势控制研究采用单质量倒立摆模型（IPM）来表示站立时的身体。然而，尚不清楚该模型的运动学假设在何种程度上以及在何种条件下是有效的。
我们的首要目标是量化IPM误差，该误差对应于无限制、自然、未受干扰站立期间踝关节与质心（COM）之间的距离变化。第二个目标是量化用踝关节角度表示COM角度时的误差。
11名年轻参与者完成了五种站立条件：睁眼（EO）和闭眼（EC）安静站立、自愿向前（VSf）和向后（VSb）摆动以及自由移动（FR）。使用改良的海伦-海斯标记模型来捕捉身体运动学。
在EO和EC期间，COM距离变化<0.1%，在VSf和VSb期间<0.25%，在FR期间<1.5%。在EO、EC和VSf时，踝关节角度与COM角度呈中度正相关，这表明踝关节角度的时间特征适度代表了COM角度的时间特征。然而，两者之间存在相当大的偏差，在使用踝关节角度估计COM角度时需要考虑这一点。对于VSb和FR，相关系数较低和/或为负，这表明用踝关节角度估计COM角度会导致较大误差。
本研究的见解对于决定何时在姿势控制研究中使用IPM以及解释相关结果至关重要。
