Loadings And Influencing Factors Of Lower Extremity During Landing Of Gymnasts In Floor Exercise

Purpose: The impact in landings was characterized by rapid, large and repeated forces that had been suggested to generate up to 70% musculo-skeletal injuries of lower extremity among gymnasts. Knowledge of external and internal loadings imposed on lower extremity by impact forces might lead help to a reduction in landing related injuries. There had been few studies that provided impact forces, external loadings of lower extremity from gymnastic landing. However, there had been little research done specially on internal loadings of gymnasts during landing. Models of subject-specific multi-body with fourteen segments and gymnastic landing mat were used to simulate movements of landing in floor exercise by Chinese elite gymnasts. Using similar approaches, internal and external loadings of lower extremity during landing were quantified, with changing of mechanical properties of landing mat and modifiable factors by gymnasts, such as ankle dorsiflexion range of motion, velocity of take-off and joint stiffness of knee and ankle. It is hoped to further understand the influence of factors on decreasing loadings of lower extremity during landing of gymnasts, thereby reducing potential risk of injury.Methods: Three elite male gymnasts volunteered to participate in this study. Participants were members of Chinese national gymnastics team and were healthy without any muscular or tendonitis injuries. Movements of gymnastic landing were captured by two high-speed video cameras(CASIO EX-F1) with 300 Hz frequency and 1/320 s shutter speed. Movements included salto backward tucked(360°), salto backward stretched with 3/2 twist(540°), salto backward stretched with 3/1 twist(1080°)connected with salto backward stretched with 3/2 twist(540°) and double salto backward tucked with 2/1 twist(720°). Using software of SIMI Motion and 3D calibration frame of PEAK, kinematic data with sixteen markers of major joints was digitizated and analysed. Computer programs by scriptlanguage of Python were used to construct interface between kinematic data and BRG.Life MOD TM. Conbined with anthropometric parameters of subject-specific participant, a model of multi-body with fourteen segments was developed in BRG.Life MOD TM and a model of gymnastic landing mat was built in software of ADAMS. And then, real performance of landing in floor exercise was reproduced succeeded based on testing validity of models. Finally, using the same approaches, kinetic data of lower extremity during gymnastic landing was analyzed with different conditions, such as different mechanical properties of landing mat, different ankle dorsiflexion range of motion, different velocity of take-off and different joint stiffness of knee and ankle.Results: Gymnastic landing was divided into three parts: early impact phase, late impact phase and buffer phase. A gymnast can produce up to 5 times body weight in groud reaction forces(GRF) during landing with salto backward tucked. There was max impulse and loading rate during the early impact phase. The peak of power was 168 W/kg and happened in left ankle. The ankle plantarflexors provided the major energy absorption, averaging 58% of the total muscluar work done, followed by the knee(21%) and hip(21%) extensors during early impact phase. During late impact phase, there was the max moment of extensor with knee and was 161 N?m in sagittal plane, but, there was the max moment of abduction with hip and was 154N?m in frontal plane. The peak of GRF, time to peak and kinematic angles of lower extremity with the same gymnastic landing task in floor exercise were collected by computer simulation based on different multi-body models. From these data, the angles of knee joint between real performance of landing and computer simulation used all models except model 4 were very similar. Model 3 was the best that reproduced real performance among fivemodels after comparing kinemactic angles of lower extremity and time errors comprehensively. The peak moment of knee extensor was decreased from model 1 to model 5 successively. On the contrary, the peak moment of knee flexor was increased from model 1 to model 5 successively. The peak moment of knee extensor of model 1 was 281 N?m and the peak moment of knee flexor of model 5 was 48 N?m. Angle of ankle joint was relatively sensitive to stiffness and dampness of landing mat. Loading rate increased by 26% when stiffness of landing mat increased by 30%. There was some influence on horizontal GRF and velocity of foot with changing of dampness of landing mat. However, there was obvious influence on the peak of joint reaction force and moment of ankle with changing of friction of landing mat. And what is more, ankle plantarflexors would provide up to 89% of addinional energy dissipation, if friction of landing mat increased by 30%. External loadings of lower extremity, knee valgus angles and moment of knee abduction would increase, but, moment of knee extensor would decrease, followed with lower ankle dorsiflexion range of motion during landing of floor exercise. If ankle dorsiflexion range of motion increased by more than 6°, the peak power of knee joint would increase by 22% at least in the frontal plane, thus, it would induce higher potential risk of ACL. There are two landings of salto backward stretched with 3/1 twist connected with salto backward stretched with 3/2 twist. Loading rate and loading rate attenuation were 172.09 BW/s and 157.45 BW/s during the first landing, and were 125 BW/s and 53.57BW/s during the second landing. During the first landing, if vertical velocity of take-off increased by 10%, the peak moment of ankle would increase by 7.7% in frontal plane and 15.1% in transverse plane. But, there was little influence on loadings of ankle with horizon velocity of take-off. During the second landing, if horizon velocity of take-off increased by 10%, the peak moment of ankle dorsi-flexors would increase by 12.8% in sagittal plane. But, if vertical velocity of take-off increased by 10%, the peak moment of ankle dorsi-flexor would decrease by 8.8%.Within initial 30 ms after toe touching landing mat, there was greater angle veolicity of knee and ankle valgus during landing of double salto backward tucked with 2/1 twist. Loading rate and loading rate attenuation were 219.5 BW/s and 88.6 BW/s. The peak moment of knee extensor increased 11.6% and knee flexor decreased 5.2% with the increase of joint stiffness of knee and ankle by 40%. On the contrary, the peak moment of knee extensor decreased 21.9%, but the peak moment of knee joint in frontal plane would increase, with decresing joint stiffness of knee and ankle by 40%. In addition, there was little influence on the peak of GRF and moment of ankle with the change of joint stiffness of knee and ankle.Conclusion: Valid and real kinematic data of landing of gymnasts could be captured by high-speed cameras with no disturbing to daily traing and competiton. GRF was computed by computer simulation. And then, external and internal loadings of lower extremity were quantified by kinetic data during gymnastic landing. This method will help to further understand potential risk of injury of lower extremity and has good significance for methodology. Multi-body model of human body with fourteen segments was the best model that could reproduce real performance of landing of a gymnast effectively. There was inconsistent sensitivity with different influencing factors. Friction of Landing mat and joint angles of lower extremity played more important roles than other in loadings of lower limbs. Although, jumping veolicity and joint stiffness were not very sensitive with loadings of lower limbs, they could contribute to improve landing quality to landing safety for gymnasts. A large increase in stiffness of landing mat could decrease angles of ankle flexor and shorten time to the peak of GRF, thereby external loadings increased. But, a large increase in dampness could increase ankle angles of flexor. However, there was little change of ankle angles with increasing of friction, internal loadings would increase obviously. Thus, the potential injury risk of ankle may increase as followed. Knee loadings in sagittal plane would increase greatly with the increase of ankle plantar flexor. In other words, knee loadings in sagittal plane would decreased obviously with the increased of ankle dorsiflexion range of motion, but knee loadings in transerve plane would increase greatly and loadings in frontal plane increase slightly, thereby gymnasts might be always at higher potential risk of ACL. There are two landings in movement of action connection. Time of loading rate attention during the first landing was short, so, loadings in lower extremity were greater than the second landing. Posture angle would decrease with increase of vertical velocity of take-off in the frist landing. There was no influence on ankle loadings and was helpful to perform the next action connection. Posture angle would increase with increase of horizon velocity of take-off in the second landing. It was helpful to improve landing quality, but internal loadings of ankle joint would increase. Great stress was exerted on knee and ankle because of great horizon GRF during landing of somersault and twist, thereby there was great moments of knee and ankle in frontal plane. There was little influence on moments of knee and ankle with the change of joint stiffness of knee and ankle. But, the peak of knee extensor would increase and knee abduction would decrease with the increase of joint stiffness of knee and ankle. Therefore, larger ankle dorsiflexion range of motion, greater friction of landing mat, horizon velocity of take-off, horizon GRF and joint stiffness are more likely to lead to injury of lower extremity because of the extreme loadings that puts on the muscles of the lower extremity.