Study Of Head And Hip Stance Characteristics Of Swimmers ——Based On The Application Of A New IMU For Swimming

ObjectiveSwimming stance is one of the important factors affecting swimming performance.Due to the lack of effective continuous measurement methods,the current knowledge of swimmer’s stance characteristics is very limited.With the gradual application of miniaturized inertial measurement units in the study of swimming kinematics,new perspectives are brought to the study of swimming stance.In this study,the head and hip stance angles and angular velocities of four swimming stances were collected and analyzed by using our own inertial measurement unit,and the body stance change characteristics in swimming were quantified in the analysis of high sampling rate and large amount of time series data,and the key head/hip stances of athletes were evaluated,which provided reference information for athletes to further improve their sports performance and provided theoretical support for future related training.The study will provide theoretical support for future training.MethodsThis study used literature,experimental,video analysis,comparative analysis and mathematical and statistical methods.The literature was systematically reviewed through online databases such as China Knowledge Network,Pubmed,Google Scholar and other related books to lay the theoretical foundation for the study.The inertial measurement unit was used to capture the stance characteristics of 18 swimmers of different sport levels in the pool and the water tank in multiple strokes with a sampling frame rate of 100 Hz,and a total of 60 sets of complete data were captured.The data were analyzed mathematically using MATLAB 2021,SPSS 25,and Excel 2021 software.Result（1）The total amplitude of butterfly head pitch angle is larger than the total amplitude of hip,and the butterfly head/hip pitch angle becomes larger and unstable in the water tank;the butterfly head/hip angle velocity has opposite peak and trough characteristics,with the head rising faster and falling slower,and the opposite for the hip;athletes with high movement level in a certain range have longer movement cycle time;（2）The head cross-roll angle of backstroke athletes is relatively stable but there is asymmetry,and the hip cross-roll angle amplitude and symmetry than the head;head angular velocity is lower than hip angular velocity;the higher the backstroke athletic grade the longer the single cycle time spent;（3）Breaststroke head pitch angle total amplitude is twice as long as the hip;head and hip angular velocity are close,peak angular velocity is about 2rad/s;short distance breaststroke shows the pitch angle angular velocity characteristics of slow before and fast after;（4）Freestyle unilateral cross-roll angle is about 40°,the average number of strokes is 10.26 times per 25 meters,and the average stroke length is 2.97 meters/time.Athletes with high freestyle rating showed greater cross-roll angle;freestyle head cross-roll angle increased about 9° in the water tank;freestyle head and hip both had asymmetry and worse hip symmetry;freestyle head and hip cross-roll angular velocity was close,and freestyle athletes’ head and hip angular velocity increased with water velocity in the water tank.Conclusion（1）The study of attitude characteristics in this paper provides diversified derivative parameters based on posture for swimming technical analysis,and provides a new perspective and possibility for further study of swimming kinematics and dynamics.The rolling posture is the key posture of freestyle and backstroke.The head / hip rolling posture has project characteristics in freestyle and backstroke,as well as some personalized characteristics.The pitching posture has typical project characteristics as the key posture of breaststroke and butterfly stroke.the head / hip pitching posture difference well reflects the body posture of breaststroke and butterfly stroke,and can be used as an important reference index for technical optimization.（2）Through the attitude angle,the parameters such as attitude angle rotation speed,action times,action cycle,action time and average stroke can be calculated,and a new method of swimming technique analysis is constructed based on the comprehensive technical analysis of multi-parameters.to provide ideas for the future digital technical analysis of swimming.Suggestion（1）Design training movements that conform to the range of body cross-roll angle in freestyle and backstroke training,use reasonable training movements within the range of pitch and elevation angle in butterfly and breaststroke,activate the training of related muscle groups need to consider trunk angular velocity and angle,and use accurate angular velocity and angle training to promote special sports performance.（2）Make full use of accurate postural angle data for technical diagnostic assessment and training monitoring,and use postural angle and other related data to develop models that refine the identification of fatigue,injury and muscle imbalance.（3）Future research can keep digging deeper into the phase relationship between stance angle and limbs of key parts such as head,shoulders and hips,and explore the slight changes in the accurate data,which may help elite athletes to break through again in technology and help a new situation of digital research in modern swimming technology.（4）Develop algorithms that meet the needs of practical applications,and sports science professionals should cooperate with algorithm developers in deep communication to develop more usable algorithms and software systems to facilitate data extractability,operability and visualization.