Major factors influencing rearfoot external eversion moment during barefoot walking

The purpose of this study, is to determine the factors that substantially influence the magnitude of rearfoot external eversion moment during the stance phase of walking. Twenty-nine healthy adult men participated in this study. The foot motion during the support phase was collected by the motion capture system (Vicon Motion Systems, Oxford, UK) at 500 Hz, and the force platform data (Type 9281E; Kistler Instruments, Winterthur, Switzerland) were collected at 1000 Hz. Participants were asked to walk barefoot along the walkway and across the force platform. The resultant moment vector acting on the ankle joint center was computed using the cross product of the vector from the ankle joint center to the center of pressure (COP) and the vector of the ground reaction force (GRF). From the moment vector, the parallel component to the longitudinal foot axis (heel to toe) was computed as the anatomically relevant total rearfoot external inversion/eversion moment due to the GRF (Mtot). The Mtot was decomposed into the moment components derived from the mediolateral GRF (Mml) and from the vertical GRF (Mv). The Mml and Mv moment components were then decomposed into each force and moment arm. For Mml, the mediolateral GRF (Fml) was the force, and the height of the ankle joint center (aH) was the moment arm. For Mv, the vertical GRF (Fv) was the force and the medio-lateral distance of the COP relative to the ankle joint center in the transverse plane (aCOPml) was the moment arm. To visualize moment changes, we first normalized the data of each participant with the entire support phase as 100% (101 points). The ensemble change of all participants was obtained as the average waveform of each participant. The average values of each moment component, force, and moment arm in Phase I and Phase II for each participant were calculated (Phase I was defined until 10% of the support phase and Phase II was defined from 10% to 60% of the support phase). To investigate the relationship between force and moment and between moment arm and moment within each moment component, correlation analyses between Fml and Mml, aH and Mml, Fv and Mv, and aCOPml and Mv were conducted for each phase. Rearfoot eversion moment was dominated by the external moment due to the mediolateral component of GRF during Phase I, and then the external moment due to the vertical component of GRF came to dominate the rearfoot eversion moment during Phase II (sheet normalized_Mtot,Mml,Mv). Correlation analysis revealed that Fml was strongly correlated with Mml, and also aCOPml was strongly correlated with Mv in both phases (sheet various parameters). We found that the magnitude of mediolateral GRF strongly associated with the rearfoot external eversion moment just after foot contact. During the subsequent phase, we found that the lateral distance of the COP relative to the ankle joint center strongly associated with the rearfoot external eversion moment.本研究旨在明确步行支撑期内显著影响后足外翻力矩大小的相关因素。本研究共招募29名健康成年男性作为受试者。采用运动捕捉系统（英国牛津Vicon运动系统公司）以500Hz的采样率采集支撑期足部运动数据，同时采用瑞士温特图尔Kistler仪器公司生产的型号9281E测力台以1000Hz的采样率采集测力数据。要求受试者赤脚沿步道行走并行经测力台。通过踝关节中心至压力中心（Center of Pressure, COP）的矢量与地面反作用力（Ground Reaction Force, GRF）矢量的叉乘，计算得到作用于踝关节中心的合外力矩矢量。基于该合外力矩矢量，沿足部纵轴（足跟至足尖）的平行分量即为与解剖学相关的、由地面反作用力产生的后足总内/外翻力矩（Mtot）。将Mtot分解为内侧-外侧地面反作用力产生的力矩分量（Mml）与垂直地面反作用力产生的力矩分量（Mv）。随后进一步将Mml和Mv分解为各自对应的力与力矩臂：对于Mml，其对应的力为内侧-外侧地面反作用力（Fml），力矩臂为踝关节中心高度（aH）；对于Mv，其对应的力为垂直地面反作用力（Fv），力矩臂为横平面内压力中心相对于踝关节中心的内侧-外侧距离（aCOPml）。为实现力矩变化的可视化，首先以整个支撑期为100%（共101个数据点）对每名受试者的数据进行归一化处理。以所有受试者各自的归一化波形的平均值，得到全体受试者的整体变化趋势。计算每名受试者在支撑期I和II阶段各力矩分量、力及力矩臂的平均值：其中阶段I定义为支撑期前10%区间，阶段II定义为支撑期10%至60%区间。为探究各力矩分量内力与力矩、力矩臂与力矩之间的关联，针对两个阶段分别开展Fml与Mml、aH与Mml、Fv与Mv以及aCOPml与Mv的相关性分析。研究结果显示，在阶段I，后足外翻力矩主要由地面反作用力内侧-外侧分量产生的外力矩主导；而在阶段II，地面反作用力垂直分量产生的外力矩成为后足外翻力矩的主导因素（详见归一化Mtot、Mml、Mv相关图表）。相关性分析结果表明，两个阶段中Fml与Mml均呈强相关，且aCOPml与Mv同样呈强相关（详见各项参数相关图表）。本研究发现，足触地后即刻的后足外翻力矩大小与内侧-外侧地面反作用力密切相关；在后续的阶段II中，压力中心相对于踝关节中心的内侧-外侧距离与后足外翻力矩显著相关。