vGRF analysis based on GRA-BP model to predict volleyball smash landing

Vertical Ground Reaction Force (vGRF) is essential for the biomechanical analysis of volleyball players. Objective: A method of constructing a coupled mathematical model of Grey Relation Analysis (GRA) and BP neural networks to predict the vGRF of volleyball players hitting the ball on the ground instead of a three-dimensional force table. method 20 second-level volleyball players from the Tianjin Institute of Physical Education were selected to demonstrate the volleyball smash action in a two-step running mode, and kinematic data and vGRF were collected synchronously using the Qualisys 8-lens infrared spot high-speed motion capture system and the Kistler three-dimensional force measuring table. Opensim was used to calculate the kinematic data of volleyball players performing a two-step running smash. GRA was used to screen kinematic indicators with a correlation of less than 0.98, root mean squared error (RMSE), mean absolute percentage error (MAPE) and mean absolute error (MAE) were used as evaluation indicators of the GRA-BP model, and Kendall's( W) coefficient evaluation was used to predict the agreement between vGRF and measured vGRF. Results: The GRA results showed that the correlation degree of 13 kinematic data such as pelvic anterior tilt angle, pelvic tilt angle and pelvic rotation angle was higher than 0.98. The root mean square error (RMSE) between the predicted value and the measured value is 0.33 BW, the mean absolute percentage error (MAPE) is 4%, the mean absolute error (MAE) is 0.29 BW, and the Kendall's W coefficient is 0.945, P≤0.001. Conclusions: The established GRA-BP model can significantly improve the accuracy of volleyball players in hitting the ball and vGRF and significantly reduce the measurement time. At the same time, the mathematical model provides data support for scientific training and better accompanies athletes' health training and participation. Finally, the model has good reproducibility and easy operation, and will also provide theoretical and practical reference for guiding national sports and scientific fitness.