Study On The Mechanical Characteristics Of Lower Limb Joints And Changes In Muscle Activation During Landing After Running Fatigue

Objective:The effects of fatigue on the kinematic and kinetic indexes of the joints of the lower extremities were analyzed by comparing the characteristics of the mechanical indexes of the joints of the lower extremities during the landing process before and after fatigue and the activation of the main muscles of the lower extremities.To investigate the activation patterns and regulatory strategies of active and antagonistic muscles after fatigue.To reveal muscle co-activation patterns during landing after fatigue and to consider potential mechanism possibilities.To assist in the development of training or rehabilitation programs with the aim of providing a theoretical basis and experimental basis for enhancing training effectiveness and preventing lower limb injuries.Methods:Twelve male subjects who met the inclusion criteria were selected.Locomotor fatigue was induced by a running fatigue protocol of 4m/s constant speed running on a running platform until fatigue requirements were reached.The joint angle changes of the hip,knee and ankle joints during the landing process before and after fatigue were tested using a three-dimensional motion capture system,and the parameters of each joint moment and ground reaction force in each direction during the landing process were recorded by the feedback from the force measurement table system.The sEMG signals of the rectus femoris,biceps femoris,anterior tibialis and hallux valgus muscles were collected by surface electromyography before and after fatigue during different stages of the landing process.The changes of all indicators before and after fatigue were also statistically processed and comparatively analyzed.Results:(1)The flexion angle and joint mobility of the lower limb joints increased during the landing process after running fatigue,and the joint angle of the hip and knee decreased at the moment of landing,and the flexion angle was significantly greater than that before fatigue(p<0.05).The joint flexion angle of the knee joint at the moment of leaving the ground also increased significantly compared with that before fatigue(p<0.05).However,there was no significant difference in the joint angle change of the ankle joint during landing(p>0.05).(2)The peak moment of knee joint during landing after running fatigue was significantly increased compared with that before fatigue(p<0.05).There was no significant difference in the peak moments of the hip and ankle joints compared with those before fatigue(p>0.05).(3)There was an increase in ground reaction force at the moment of stirrups during landing after running fatigue.The second peak of vertical ground reaction force was significantly increased compared with that before fatigue(p<0.05).The first peak of vertical ground reaction force was not significantly different from that before fatigue(p>0.05).(4)The activation level of the rectus femoris muscle was increased during the landing process after running fatigue.rms was significantly higher than before fatigue(p<0.05).mpf was lower than before fatigue(p<0.05),indicating that muscle fatigue occurred in the rectus femoris muscle.(5)After running fatigue,the activation level of the biceps femoris was elevated during the pre-activation period during landing.rms was significantly higher than before fatigue(p<0.05).(6)After running fatigue,the activation level of the tibialis anterior muscle during landing was elevated in the pre-landing period.rms was significantly higher than before fatigue(p<0.05).The MPF was lower during the whole process of landing than before fatigue(p<0.05),indicating that muscle fatigue occurred in the tibialis anterior muscle.(7)After running fatigue,the activation level of the gastrocnemius muscle was elevated during the pre-activation period and the late landing period during landing.rms was significantly higher than before fatigue(p<0.05).The onset of muscle fatigue was detected in both the pre-and post-landing periods.mpf was lower than pre-fatigue(p<0.05).(8)There was no significant difference in the change in the co-activation ratio of antagonistic muscles during the pre-activation period compared to the pre-fatigue period(p>0.05).The antagonist muscle co-activation ratio was significantly lower(p<0.05)in both the pre-landing and post-landing periods,indicating that the antagonist muscle co-activation strategy changed with fatigue after landing.Conclusions:(1)After running fatigue,the lower limb joints showed different mechanical characteristics during the landing process.The greater hip and knee flexion angle and greater joint mobility at the moment of landing and leaving the ground,as well as the greater knee moment and higher vertical ground reaction force during stirrups,are the important reasons for the lower limb joint injury after running fatigue.(2)The rectus femoris,biceps femoris,tibialis anterior and gastrocnemius muscles all enhance muscle activation during landing after running fatigue,aiming to recruit more motor units to compensate for the lack of strength and decreased joint stability caused by fatigue.(3)Fatigue leads to adjustments in muscle co-activation strategies.This is mainly reflected in the reduction of antagonist muscle co-activation level after landing to compensate for the lack of active muscle strength caused by fatigue.The mechanism may be that fatigue triggers a change in the regulation of active muscle motoneurons in the higher centers,which disrupts the original cross-inhibition balance and leads to a change in the innervation pattern of antagonist muscle motoneurons.Such changes can reduce joint stability and negatively affect runner health.