| Objective:This study was conducted by comparing the characteristics of changes in lower extremity kinematic and kinetic indices and changes in muscle activity during the completion of the lateral cut task before and after kinematic fatigue.We analyzed whether there were differences in the changes in lower extremity kinematics,kinetics and muscle activity during the completion of the lateral cutting maneuver at different fatigue levels and whether these differences could cause adverse changes in the lateral cutting maneuver pattern,which could lead to the occurrence of injury.To provide theoretical support and experimental basis for the prevention of lower extremity injuries in lateral cutting tasks caused by fatigue factors.Methods:Sixteen male subjects who met the inclusion criteria were selected and fatigue was induced by using the "run+jump" fatigue protocol,and the average decay rate of longitudinal jump height and RPE scale were used to define the degree of fatigue in order to meet the requirements of locomotor fatigue.Afterwards,the joint angle changes of the hip,knee and ankle joints in the lateral cut task before fatigue,after fatigue and after exhaustion were tested by using a three-position motion capture system,and the parameters of hip,knee and ankle joint moments and ground reaction forces in each direction were recorded by the feedback from the dynamometer system;the sEMG signals of the gluteus maximus,gluteus medius.rectus femoris,hamstring,tibialis anterior and gastrocnemius muscles in the lateral cut task under different fatigue levels were collected by surface electromyography.The sEMG signals were collected by surface electromyography,and the differences of all indicators at different fatigue levels were statistically processed and comparatively analyzed.Results:(1)There were significant differences in hip flexion angle,knee flexion angle,knee valgus angle and knee valgus moment between different levels of fatigue at the moment of touchdown of the lateral cut movement(P<0.01:P<0.01;P<0.01;P<0.01).Compared with pre-fatigue,the change in hip flexion angle and knee flexion angle were significantly lower and the change in knee valgus angle was increased after fatigue;the change in hip flexion angle and knee flexion angle were significantly lower.the change in knee valgus angle and the change in knee valgus moment were increased after force exhaustion.Compared to post-fatigue,post-exhaustion hip flexion angle change,knee flexion angle change significantly decreased,knee valgus angle change.and knee valgus moment change increased.(2)There were significant differences in hip internal rotation angle,knee flexion angle,knee valgus angle,ankle dorsiflexion angle,knee extension moment,knee valgus moment and knee internal rotation moment between different fatigue levels at the moment of maximum knee flexion angle in the lateral cut movement(P<0.05:P<0.01;P<0.01;P<0.01;P<0.01;P<0.01;P<0.05).Compared to pre-fatigue,the changes in hip internal rotation angle,knee flexion angle and knee internal rotation moment were significantly lower and the changes in knee valgus angle,knee extension moment and knee valgus moment were increased after fatigue:the changes in hip internal rotation angle,knee flexion angle,ankle dorsiflexion angle and knee internal rotation moment were significantly lower and the changes in knee valgus angle,knee extension moment and knee valgus moment were increased after force exhaustion.Compared to post-fatigue,the changes in hip internal rotation angle,knee flexion angle and knee internal rotation moment were significantly lower and the changes in knee extension moment and knee valgus moment were increased after exhaustion.(3)There were significant differences in hip internal rotation angle,knee flexion angle,knee valgus angle,knee internal rotation angle,hip extension moment,knee extension moment and knee valgus moment between different levels of fatigue at the moment of peak ground reaction force of the lateral cut movement(P<0.01;P<0.01;P<0.05;P<0.05;P<0.05;P<0.05;P<0.01).Compared with pre-fatigue,the changes in hip internal rotation angle,knee flexion angle and hip extension moment were significantly lower and the changes in knee valgus moment were increased after fatigue;the changes in hip internal rotation angle,knee flexion angle and hip extension moment were significantly lower and the changes in knee valgus angle,knee internal rotation angle,knee extension moment and knee valgus moment were increased after force exhaustion.Compared with post-fatigue,the changes in hip internal rotation angle and hip extension moment were significantly lower and the changes in knee external rotation angle were increased after force exhaustion.(4)The peak vertical ground reaction force was significantly different between fatigue levels(P<0.05).The change in peak vertical ground reaction force increased after fatigue compared to before fatigue:the change in peak vertical ground reaction force also increased after force exhaustion.(5)During the lateral cut movement support phase.MPFs of gluteus maximus.gluteus medius.rectus femoris.hamstrings,tibialis anterior and gastrocnemius were significantly different between different levels of fatigue(P<0.01;P<0.01;P<0.01;P<0.01;P<0.05;P<0.01).This indicates that fatigue occurred in all muscles after fatigue and after force exhaustion.There were significant differences in IEMG between different levels of fatigue for the gluteus maximus.gluteus medius.rectus femoris,hamstrings and tibialis anterior(P<0.01:P<0.01:P<0.05;P<0.05;P<0.05).Compared to pre-fatigue.IEMG of gluteus maximus.gluteus medius.rectus femoris.hamstrings and tibialis anterior were all significantly reduced after fatigue;IEMG of gluteus maximus.gluteus medius.hamstrings and tibialis anterior were all significantly reduced after exertion.The IEMG of the gluteus maximus and gastrocnemius all decreased significantly after exhaustion compared to after fatigue.This indicates a gradual decrease in the activity level of the muscles.Conclusion:(1)Exercise-induced fatigue can lead to alterations in the biomechanics of the lower limb during lateral cutting movements.A reduction in hip flexion can lead to a reduction in the ability to cushion ground reaction forces.A reduction in knee flexion leads to an increase in shear forces on the anterior tibial translation and a more ’stiff landing strategy.These changes are more pronounced when fatigue increases to a state of exhaustion.Changes in these factors can negatively affect the lateral cutting movement.(2)Exercise-induced fatigue can lead to an increase in knee valgus moment,which can have a negative effect on knee stabiliy.It also increases the peak vertical ground reaction force and peak load rate in lateral cutting movements which is an important factor in lower limb injuries.These changes are more pronounced when fatigue increases to a state of force exhaustion.(3)Muscle fatigue occurs in the gluteus maximus,gluteus medius.rectus femoris,hamstrings,anterior tibialis and gastrocnemius during the course of the support phase of the lateral cut movement after exercise-induced fatigue,and the muscle activity levels of the gluteus maximus.gluteus medius,rectus femoris,hamstrings and anterior tibialis are reduced,and these changes may lead to reduced stability in the joints of the lower limbs and reduced cushioning against ground impact.The changes in muscle activation are more pronounced when fatigue levels increase to a state of exhaustion. |
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