Effects Of Fatigue And Foot Posture On Biomechanical Characteristics For Male Collegiate Volleyball Players During Single-leg Drop Landing

Objective:Volleyball is fast,fierce and high intensity team sport event.Foot is the starting part of the lower extremity movement chain during landing,then foot posture may affect the force transfer from the ankle to the knee.It could increase the risk for lower extremity injury.Stop-jumping and landing including different foot landing postures,continuous repeated take-off and landing movements are very common during training and competitions,which greatly induce exercise fatigue.The decline of neuromuscular function caused by sports fatigue is one of the key reasons of lower extremity for volleyball players.The study simulated actual competition situation by volleyball specific exercise-induced fatigue test,and explored the change characteristics of foot landing posture,pre-and-post exercise-induced fatigue on trunk and lower extremity biomechanics for volleyball collegiate students during single-leg drop landing at initial contact,to reveal the possible mechanism of non-contact anterior cruciate ligament injuries and rules of volleyball players’ lower extremity biomechanics during drop landing,which provided theoretical reference for the research of volleyball players’ training and injury prevention.Methods:20 volleyball male collegiate students were recruited in the study.3D motion capture system（Nokov）and force platform（Betec）were used to collect kinematic and kinetic parameters during three different foot posture and pre-and-post fatigue protocol in single-leg drop landing.Cortex-64 2.6.2.1169 software was used to identify and process the kinematic data.The joint three-dimensional moment was calculated by inverse dynamics method.Joint moment was normalised to the product of each participant’s height and mass.The effects of different foot landing postures on the Kinematics and Kinetics of the trunk and lower extremity pre-and-post fatigue were determined by 2×3 repeated measurement two-way analysis of variance（ANOVA）,comparing the difference of pre-and-post fatigue by paired t-test,one-way ANOVA was used to identify the difference of foot posture,and the effect size were calculated.The effect size of two-way and one-way ANOVA were expressed by η²,while the paired t-test was expressed by r_pb².Results:（1）Fatigue and foot posture on the hip flexion angle showed significant interaction（F[2,57]=3.477,p=0.038,η²=0.11）effect at the initial contact.Compared to pre-fatigue,post-fatigue on Toe-in(p<0.001,r_pb²=0.52),Toe-out(p<0.001,r_pb²=0.53)and Toe-neutral(p<0.001,r_pb²=0.44)were showed the hip flexion angle decreased.Pre-fatigue（p=0.041,p=0.034,η²=0.24）and post-fatigue（p<0.001,p=0.028,η²=0.46）,the Toe-in in hip flexion angle than the Toe-out and Toe-neutral were reduced.（2）Exercise-induced fatigue and foot posture in the hip rotation angle（F[2,56]=20.167,p<0.001,η²=0.42）,knee rotation moment（F[2,52]=5.199,p=0.009,η²=0.17）existed significant interaction at the first peak of ground reaction force.Post-fatigue than pre-fatigue on Toe-in was shown greater hip internal rotation angle(p<0.001,r_pb²=0.63),knee internal rotation moment(p<0.001,r_pb²=0.56).Pre-fatigue（p<0.001,η²=0.88）and post-fatigue（p<0.001,η²=0.95）,the Toe-in than Toe-out and Toe-neutral showed a larger angle of hip internal rotation angle.Compared to Toe-out and Toe-neutral,the Toe-in showed a larger moment of knee internal rotation moment post-fatigue（p=0.001,p<0.001,η²=0.27）.（3）No matter what foot posture,compared to pre-fatigue,post-fatigue showed smaller trunk anterior inclination angle(p<0.001,r_pb²=0.64),hip external valgus angle(p<0.001,r_pb²=0.20)and moment(p=0.028,r_pb²=0.08),knee flexion angle(p<0.001,r_pb²=0.24),a larger trunk inclination toward the landing side angle(p=0.035,r_pb²=0.08)and knee external valgus angle(p<0.001,r_pb²=0.42)and moment(p<0.001,r_pb²=0.57),knee internal rotation moment(p=0.026,r_pb²=0.09),higher relative height of center of mass(p<0.001,r_pb²=0.32)at the initial contact;No matter what pre and post fatigue,compared to Toe-out and Toe-neutral,Toe-in showed a larger angle of trunk inclination toward the landing side angle（p<0.001,p=0.002,η²=0.39）,hip internal rotation angle（p<0.001,p=0.035,η²=0.30）and knee external valgus angle（p<0.001,p=0.035,η²=0.77）and moment（p<0.001,p=0.005,η²=0.4）,knee internal rotation angle（p<0.001,p=0.025,η²=0.34）,and smaller hip external valgus angle（p<0.001,η²=0.67）,knee flexion angle（p=0.033,p<0.001,η²=0.32）at the initial contact.In addition,Toe-in appeared to be smaller knee flexion moment than Toe-neutral.（4）No matter what foot posture,compared to pre-fatigue,post-fatigue showed smaller hip flexion angle(p=0.014,r_pb²=0.10),knee flexion moment(p=0.001,r_pb²=0.18),and greater knee external valgus moment(p<0.001,r_pb²=0.27),higher relative height of center of mass(p=0.011,r_pb²=0.11)at first peak of ground reaction force;No matter what pre and post fatigue,compared to Toe-out and Toe-neutral,Toe-in showed smaller hip internal valgus angle（p<0.001,p=0.026,η²=0.55）,and larger hip internal valgus moment（p<0.001,η²=0.70）,knee external valgus angle（p<0.001,η²=0.93）,knee external valgus moment（p=0.001,p=0.003,η²=0.24）,knee internal rotation angle（p<0.001,η²=0.84）at the first peak of ground reaction force.（5）No matter what foot posture,pre-fatigue than post-fatigue showed a large the first peak of ground reaction force(p<0.001,r_pb²=0.58)and the loading rate(p<0.001,r_pb²=0.31).Conclusions:（1）No matter what foot posture,post-fatigue trunk anterior inclination angle,hip and knee flexion angle were reduced at the initial contact,and the first peak of ground reaction force only showed the smaller hip flexion angle,which were made relative height of center of mass increase and caused more upright landing posture.The first peak of ground reaction force and loading rate had increased obviously post-fatigue,these were likely to lead to increasing risk of ACL injury.No matter what foot posture,the knee external valgus moment was larger at the initial contact and the first peak of ground reaction force after fatigue,and the knee external valgus angle was also larger at the initial contact,which might further increase the risk of ACL injury.（2）No matter what pre and post fatigue,compared to Toe-neutral and Toe-out,Toe-in had a significant effect on the trunk and biomechanics of lower extremity（such as increasing angle of trunk inclination toward the landing side angle,knee valgus and tibial rotation）at the initial contact and the first peak of ground reaction force,were more likely to cause an ACL injury risk increases,should avoid changing toe direction excessively inward.（3）The joint effect of fatigue and foot posture led to the adverse lower extremity biomechanics changes of volleyball players who completed single-leg drop landing,which greatly decreased hip flexion angle,increased hip internal rotation Angle and knee internal rotation moment and led to higher risk of non-contact anterior cruciate ligament injury.Suggestions:The gluteus maximus was the major neuromuscular that control trunk anterior inclination and hip three-dimensional stability.Therefore,increasing the trunk anterior inclination angle as the main training objective,and strengthening the hip extensor muscles（gluteus maximus）strength and endurance training,so that they could effectively control the trunk flexion on landing and to emphasize more flexion landing posture in future training to reduce the risk of ACL injury.Landing in Toe-in posture was more likely to increase ACL injury.Toe-in posture should be avoided to prevent knee valgus and internal rotation in future training.