跑步疲劳进程中下肢生物力学模式的非线性变化研究

目的:确定跑步疲劳进程中下肢生物力学模式的变化,包括垂直和前后地面反作用力(ground reaction force,GRF)、垂直地面反作用力(vertical ground reaction force,vGRF)负载率、关节力学和刚度。方法:14名男性受试,采用Vicon红外摄像头和Bertec三维测力跑台,每隔2 min采集受试疲劳干预中的15 s GRF数据以及标记点轨迹。受试需穿着统一的跑鞋在测力跑台以恒速3.33 m/s跑至疲劳。满足以下标准时,干预结束:1)最大心率大于当下年龄的90%;2)受试不能继续跑步。对比受试跑至疲劳进程中4个时刻(疲劳前、33%、67%和100%)的着地冲击和下肢三关节触地角度、最大角度、关节活动度、角度变化量、关节蹬伸力矩和刚度等特征,采集并分析受试安静状态、疲劳后即刻、疲劳后4 min、疲劳后9 min的血乳酸浓度。结果:与疲劳前相比,1)血乳酸浓度在疲劳后即刻、疲劳后4 min和疲劳后9 min均显著增加;2)垂直/前后矢状轴GRF和vGRF负载率等参数在疲劳干预过程中均未观察到显著性变化;3)髋关节活动度在疲劳过程的33%、67%和100%时刻显著增加,膝关节活动度在67%时刻显著增加;4)踝关节运动学及踝、膝和髋关节的蹬伸力矩峰值均无变化;5)垂直刚度在67%和100%时刻显著降低。结论:疲劳干预过程中,GRF特征参数均没有明显变化,但是观察到下肢运动学和动力学模式的非线性改变。特别是从疲劳干预中期开始,人体下肢通过增加髋、膝关节活动度并减小垂直刚度实现“软着陆”策略,维持相似的冲击力特征,以减小长时间跑步可能带来损伤的风险。

Nonlinear Adaptations in Lower Extremity Biomechanics during a Fatiguing Run

Objective:This study aimed to determine the changes in lower extremity biomechanics during running-induced fatigue intervention,including vertical/anterior-posterior ground reaction force(GRF),vertical GRF(vGRF)loading rate,joint mechanics and stiffness.Methods:14 male recreational runners were recruited.GRF and marker trajectories were recorded for 15 s intermittently every 2 min to quantify the impact forces during the fatiguing run by Bertec splitbelt instrumented treadmill and Vicon 3D motion capture system.Participants were required to wear unified cushion shoes and run at 3.33 m/s until they could not continue running.They were considered fatigue,and intervention was terminated when both following criteria were met:1)The HR of the participants reached 90% of their age-calculated maximum HR;2)the participants could not continue running.The impact force,joint angles at initial contact,maximum joint angles,joint ranges of motion,changes in joint angle,joint extension torque,and stiffness in four phases of fatigue running were compared.Blood lactate concentration(BLa)was also collected before,immediately after fatigue,4 min and 9 min after fatigue.Results:Compared with the beginning of the run duration,1)BLa significantly increased immediately after running,and 4 min and 9 min after running;2)no changes were observed in vertical/anterior-posterior GRF and vertical GRF loading rates;3)the hip joint range of motion(θROM)significantly increased at 33%,67%,and 100% of the running duration,whereas θ_ROM of the knee joint significantly increased at 67%;4)no changes were observed in ankle joint kinematics and peak joint moment at the ankle,knee,and hip;5)vertical stiffness decreased at 67% and 100% of the running duration.Conclusions:GRF characteristics did not vary significantly through fatiguing run.However,nonlinear adaptations in lower extremity kinematics and kinetics were observed.In particular,a“soft landing”strategy,achieved by an increased θ_ROM at the hip and knee joints and a decreased vertical stiffness,was initiated from the mid-stage of a fatiguing run to potentially maintain similar impact forces and reduce the potential risk of injury in prolonged running.