Biomechanical Research On The Landing Impact In The Ankle Of High-level Gymnasts

PurposeGymnastics is a popular sport.Gymnasts always end with landings in their training and competition,but the success rate of the landings is low while the injury incidence of the ankle is high.This study aimed to simulate human-body dynamics of landings based on sports tests,and by using a finite element model of ankle to explore landing impact and ankle injuries in the two dimensions regarding the internal and external joints load and the stress and strain of ankle.Methods1.Sports Tests:(a)Six male gymnasts from the National Gymnastics Team were recruited to perform vertical landings from different heights(H1: 35 cm,H2: 55 cm and H3: 85 cm)and backward somersault(BS)landings in the lab of China Institute of Sport Science.The 3D motion data,electromyography(EMG),and vertical ground reaction force(vGRF)data were simultaneously recorded separately by the Qualisys Oqus motion capture system,the surface EMGs system,and the force plate respectively.These EMGs were recorded for rectus femoris(RF),biceps femoris(BF),tibialis anterior(TA),and lateral gastrocnemius(LG)on the two lower extremities of the gymnasts.(b)One of the gymnasts performed the Salto backward stretched with 2/1 turn(S720)landing in the gymnasium of the National Gymnastics Team.The 3D motion data and EMGs were simultaneously recorded separately by the 3D motion photography and the surface EMGs system,respectively.(c)During the 13 th national games for floor exercise,3D motion data were recorded for Salto backward stretched with 3/1 turn(S1080)landing,and the optimal movement was selected for further analysis.2.Computer simulation of human multi-body: one trial of BS,and S1080,S720 landings of the previous sports tests were simulated.The software of LifeMod/ADAMS with athlete-specific multibody(19-segments and 50 degrees of freedom)and gymnastics mat model were developed for simulation,while the vGRFs,lower limb joint reaction force and torques were obtained.3.Simulation of Ankle Finite Element: one gymnast was recruited to conduct CT and MRI images collection.Based on these data,the ankle finite element model(FEM)was developed,which included the lower part of tibia and fibula,all the skeleton and articular cartilage of foot,and the geometric information of the ligament around the ankle,peripheral soft tissue,and plantar plate.The displacement of the surface of tibia and fibula were fixed,and frictional contact was set up between plantar surface and the plate.The peak vGRFs(PvGRF)for the movements were applied upon the bottom of the FEM through the plate,respectively.Consequently,the stress and strain distribution of the corresponding bones of the ankle were obtained.Results1.Sports test results: Corresponding PvGRFs for different height and BS landings were: 4.62 ± 0.50 BW(body weight)(H1),6.64 ± 1.25 BW(H2),8.94 ± 0.51 BW(H3)and 11.9 ±1.50 BW(BS).The loading rate,impulse and dynamic stability coefficient in landings of H1,H2,H3,and BS increased successively.In the two kinds of landing,there was no significant difference between the time of maximum angular velocity reached for hip or knee joints and the time for PvGRF.However,the time for ankle joints was obviously earlier than all of them,and its angular velocity was the greatest in the lower limb joints.The EMGs of lower limbs maintained in high level continuously increased during the landing and reached their maximum in the terminal impact-phase.2.Multi-body simulation results: PvGRFs of gymnastics BS,S720 and S1080 landings were 11.9 BW,16.8 BW and 18.3 BW,respectively.During T0(100 ms preceding touchdown),angles of hip,knee and ankle of the S720 were almost unchanged.But those angles flexed by 27°,6° and 22° respectively in S1080,with left foot touchdown earlier than the right for 4-8 ms.During T1(from touchdown to PvGRF),the lower limb joints in BS,S720 and S1080 landings flexed faster than T0.During T2(from PvGRF to 1 BW),the angle of lower limb joints in BS remained stable,while the lower limb joints in S720 and S1080 continued to flex.Further,the flexion in S1080 was the greatest compared with the others.In the three kinds of BS,the joint reaction force of ankle was the greatest in lower limb joints,and that of hip was the lowest.The lower limb joints torques showed flexor torques during T1 and extensor torques during T2.The torques in T2 was much greater than that of T1.Except for T2 of S1080,the stiffness of hip was the greatest in lower limb joints,and that of ankle was the lowest.Meanwhile,the stiffness in T2 were greater than those of T1.But the ankle stiffness was greater than knee stiffness in S1080 during T2.3.Finite element simulation results: The high Von Mises and Tresca stresses areas were located around the edge of the lower end of the tibia and fibula in the ankle joint surface.The stress centered on the lateral anterior tibial surface.The high Von Mises and Tresca stresses areas were located around the edge of the of the talus in the ankle joint surface and the stress centered on the anterior of the outer margin of talus trochlea.The maximum Tresca stress was greater than that of Von Mises stress,and increased with the increment of landing heights and the movement difficulties.The deformation of the lower fibula of the lateral malleolus was the largest in the ankle.Conclusions1.Compared with vertical landings,gymnastics landings have smaller range of motion,greater impact forces,higher loading rate and muscle activation level,and more complex landing load pattern in lower limb joints.It is suggested that vertical landing can’t reflect the actual gymnastics landings.2.Compared with general landings,the difficult gymnastics landing requires lower limb joints flex beforehand to prepare for landing.In gymnastics landings of different difficulties,lower limb joints flex actively and rapidly to cushion landing impact during the initial impact-phase and then extend to resist the landing impact during terminal impact-phase of the landing.3.The stress on the anterior of the ankle joint surface,and the medial and lateral malleolus was higher than that of others areas,and the deformation of the lower fibula was the greatest during the gymnastics landings.These results suggest that the mechanical characteristics of gymnastics landing are the main reason for ankle impingement syndrome and stress fracture of the lateral malleolus.The findings of this study expand our knowledge of the biomechanics of gymnastics landing impact,and deepen our understanding of the biomechanical mechanism of ankle impingement syndrome,and provide a scientific theoretical basis for the prevention,treatment and rehabilitation for gymnasts’ ankle injury.