Changes in segment coordination variability and the impacts of the lower limb across running mileages in half marathons:Implications for running injuries

Background:Segment coordination variability(CV)is a movement pattern associated with running-related injuries.It can also be adversely affected by a prolonged run.However,research on this topic is currently limited.The purpose of this study was to investigate the effects of a prolonged run on segment CV and vertical loading rates during a treadmill half marathon.Methods:Fifteen healthy runners ran a half marathon on an instrumental treadmill in a biomechanical laboratory.Synchronized kinematic and kinetic data were collected every 2 km(from 2 km until 20 km),and the data were processed by musculoskeletal modeling.Segment CVs were computed from the angle-angle plots of selected pelvis-thigh,thigh-shank,and shank-rearfoot couplings using a modified vector coding technique.The loading rate of vertical ground reaction force was also calculated.A one-way MANOVA with repeated measures was performed on each of the outcome variables to examine the main effect of running mileage.Results:Significant effects of running mileage were found on segment CVs(p≤0.010)but not on loading rate(p=0.881).Notably,during the early stance phase,the CV of pelvis frontal thigh frontal was significantly increased at 20 km compared with the CV at 8 km(g=0.59,p=0.022).The CV of shank transverse vs.rearfoot frontal decreased from 2 km to 8 km(g=0.30,p=0.020)but then significantly increased at both 18 km(g=0.05,p<0.001)and 20 km(g=0.36,p<0.001).Conclusion:At the early stance,runners maintained stable CVs on the sagittal plane,which could explain the unchanged loading rate throughout the half marathon.However,increased CVs on the frontal/transverse plane may be an early sign of fatigue and indicative of possible injury risk.Further studies are necessary for conclusive statements in this regard.