Biomechanical Study On Gate Turning Technique Of Sitting Skiers In Winter Paralympic Alpine Skiing

Objective: The goal of the sports technique diagnosis based on the motion analysis is to explore the principle of motion and obtain the optimal technique.The Para alpine skiing is different from the Olympic alpine skiing because of the particularity of competition rules,participants,venue characteristics and sports equipment.In view of the Para athletes' physical shape and functional classification,combined with the training needs,this paper analyzes the motion technique and the principle of the gate turning of the sitting-alpine-skiing.The objective of the study is as followed:(1)to analyze the relationship between the Body Segment Inertial Parameters of the disabled and the class based on the evidence-based classification,so as to provide the ratio-scaled measure for the analysis of the sports technique of the disabled athletes.(2)to research the technical characteristics and principles of sitting-giant-slalom in Para alpine skiing,and analyze the essential points and kinematic indexes that affect the sport performance of the event in order to provide analysis parameters for the technical diagnosis and optimization.Method: Seventeen Paralympic amputees were selected as subjects in research on Body Segment Inertial Parameters of the amputees.The mass and the Center of Mass of the residual limb were measured by Mohsen method.The results were compared to the longitude COM obtained by calculation of multi-segment system and Zatsiorsky's model and Zheng's model to test the validity.In the study of the sport principles for sitting-giant-slalom in Para alpine skiing,eleven skiers of 4 classes were selected from the seventeen former sitting athletes as the subjects.Making use of UAV and wearable inertial measurement unit,body posture data were obtained and were used to analyze the kinematics indexes in the subsection course with 3 gates.Then,referring to the sport classes of the subjects,the characteristics and performance differences of gate turning technique as well as the key indicators affecting sports performance of different classes were analyzed.Finally,the inverted pendulum model was used to simulate the skiing trajectory and time,and the simulation results were compared with the actual distance and time to verify the validity of the model.Results:(1)The longitude COM of the lower limb amputees was,and the relative value was.There was significant difference between the above-knee amputees and the below-knee ones(P=0.01),and there was significant difference between the amputees and the able-body people(P=0.00).(2)The values of one-dimensional COM calculated by model M1,M2 and M3 were significantly different from the results measured by balance board test(P<0.00).(3)The regressive results of the regression model and the scaling factor of the length were significant consistent with the measured values obtained by Mohsen method(ICC=0.89).(4)There was no significant difference in the whole distance among different classes and genders(p > 0.05),but it was inverse for the sport performance among different classes(p = 0.00).There was a significant positive correlation between the sport performance and the whole distance,the minimum distance from the gate,the horizontal distance from the gate,the track length and time of the subsection course respectively.There was a significant correlation between the class and the whole time(r=-0.92,p=0.00)and the length(r=0.46,p=0.01)of the target course.(5)There was a significant negative correlation between the maximum velocity and the skiing time for LW10 and LW11(r=-0.76,p<0.01).The correlation between the skiing time and the velocity change during gate turning was significant for LW12(r=0.56,p=0.02).There was a significant negative correlation between the velocity change and the athlete's class(r=-0.38,p=0.03),and a significant positive correlation between it and the position where the minimum velocity appeared(r =0.40,p=0.02).(6)Compared with the skiing distance and time,the simulation results of inverted pendulum model had no significant difference(p > 0.05),and the consistency of the results is ICC = 0.45 and ICC = 0.85 respectively.Conclusion:(1)The mass of the residual limb can be estimated by using the scaling factor of the length and the anthropometric regression model,especially for the above-knee amputation.However,the COM of the residual limb calculate by scaling factor of the length will lead to a large error.(2)There was no significant difference in body COM between the results calculated by Mohsen method combined with anthropometric regression model and the true position measured by the balance board test,and there was a high correlation between them,all of which showed that the Mohsen method was valid in calculating the mass and COM of the residual limb.(3)The turning trajectory with direction-change appeared before the gate was less than that after the gate.Therefore,completing the body turning before the gate was more conducive to improving the performance.(4)There was no statistical correlation between the maximum velocity and the time and distance both for the single gate and the subsection course for LW12,but the velocity change before and after the gate turning was directly related to the performance for both target course.The trajectory length,turning radius,the minimum distance from the gate and the velocity change before and after the gate turning could not only analyze the kinematics of the single gate,but also effectively reflected the performance of the whole course.