| Background and objective:Anterior cruciate ligament(ACL)injury of knee joint has the highest incidence during sidestep cutting.Trunk motion state may be an important risk factor for ACL injury,trunk forward tilt may reduce the risk of non-contact ACL injury.However,the relationship between trunk posture and knee joint motion in ACL injury is not clear,so it is important to study knee joint motions under different trunk motion states for exploring the mechanism of ACL injury.In related research of high injury risk movements such as sidestep cutting,it is usually assumed that volunteers’ dominant and non-dominant lower extremities moved symmetrically so as to facilitate data collection and analysis.However,it has not been studied whether the two lower extremities under different trunk motion states during sidestep cutting can be assumed symmetrically.On the basis of previous studies,this study will further explore the effects of trunk motion state on knee biomechanics during sidestep cutting,and further clarify the injury risk of bilateral knee joints,in order to provide theoretical basis for the prevention of ACL injury.Methods:Twenty healthy male college basketball athletes volunteered to take part in this research.Athletes played sidestep cutting under trunk forward tilt and trunk natural state,the movements were tested by VICON three-dimensional motion capture system,NORAXON surface electromyography(EMG)test system and KISTLER force platform synchronously.The knee joint flexion angle and varus angle at initial contact,the knee joint peak angle and peak torque after initial contact,the muscle activities of vastus medialis,vastus lateralis,biceps femoris,semitendinosus during pre-activity phase and post-contact phase were collected when the dominant or non-dominant lower extremities were used as weight-supporting leg,respectively.Statistical analysis took the average of three successful tests,repeated measure two-way ANOVA analysis were used to investigate the effect of trunk motion states,side-to-side difference on knee joint kinematics,kinetics and EMG.P<0.05 was considered statistically significant.Results:1.Effects of trunk motion states on knee joint biomechanics in sidestep cutting1.1 Comparison of muscle activities under different trunk motion states during pre-activity phase: compared with the trunk natural state,there was no significant differrence of knee joints muscle activity included vastus medialis,vastus lateralis,biceps femoris,semitendinosus,quadriceps femoris,hamstrings and H/Q ratio when the trunk is forward tilting during pre-activity phase(P>0.05).1.2 Comparison of biomechanical results of knee joint in different trunk motion states at initial contact time: trunk motion state has significant influence on knee joint flexion angle and varus angle at initial contact time(P<0.01).Whether for dominant or non-dominant lower extremities,knee joint flexion angle and varus angle are significantly larger under trunk forword tilt than those at natural state of trunk.1.3 Biomechanics comparisons of different trunk motion states after contacting the ground:As for kinematics results,the trunk motion state has a significant influence on the peak flexion angle of knee joint after touching the ground(P<0.01).For both dominant and non-dominant lower extremities during sidestep cutting under trunk forward tilt,the knee joint peak flexion angle is significantly larger than that of the trunk natural state.Regarding the kinetics results,when the athletes were playing sidestep cutting under the trunk forward tilt state,the peak valgus torque of the dominant knee joint was significantly greater than that of the trunk natural state(P<0.05).On the results of EMG,for the dominant side,the H/Q ratio(the ratio of hamstring muscle to quadriceps femoris)and hamstrings activity under trunk forward tilt was significantly higher than trunk natural state(P<0.05).For the non-dominant side,there was no significant difference of knee joint muscle activities and H/Q value during sidestep cutting under two different trunk motion states(P>0.05).2.Side-to-side biomechanical differences of knee joint during sidestep cutting.Before the initial contact,the muscle activities around the knee and H/Q ratio had no significant difference between two lower extremities during pre-activety phase under different trunk motion states(P>0.05);at initial contact time,there was no significant difference in the knee joint angles between the dominant and non-dominant sides under different trunk motion states(P>0.05);after contacting the ground,when trunk tilt forward,the activity of semitendinosus and hamstrings of dominant side was significantly higher than the non-dominant side(P<0.05);after contacting the ground,when trunk in natural state,there was no significant difference in the knee joint biomechanics between the dominant and non-dominant sides(P>0.05).Conclusions and significance:1.The influence of trunk motion states on knee joint biomechanical during sidestep cutting.Generally speaking,the trunk motion state has a significant influence on the knee joint flexion angle at initial contact,the varus angle at initial contact,the peak flexion angle,the peak valgus torque and the H/Q ratio after initial contact.When the trunk tilt forward,the knee joint flexion angle at initial contact and the peak flexion angle is larger during sidestep cutting,which may have the protective effect on ACL.However,when the trunk tilt forward during sidestep cutting,the peak valgus torque of the dominant knee joint is larger compared with trunk natural state.Therefore,in the daily training and competitive guidance of athletes,the role of trunk forward control should be applied reasonably.The knee valgus torque of dominant leg should be avoided as far as possible while increasing the trunk forward tilt,so as to effectively reduce the risk of ACL injury.2.Side-to-side biomechanical differences of knee joint during sidestep cuttingThe influence of trunk motion states on the dominant and non-dominant knee joints is different.When the trunk tilt forward,the dominant lower extremity hamstrings muscle is more active which may have protective effect on ACL.Under the two trunk motion states,there is no significant difference in the kinematics and kinetics results between the dominant and non-dominant knee joints.In conclusion,the knee joint of the non-dominant side may be more vulnerable to injury during the sidestep cutting under the trunk forward state. |
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