Video analysis of the deformation and effective mass of gymnastics landing mats.

INTRODUCTION Landing mats that undergo large area deformation are now essential for the safe completion of landings in gymnastics. The aim of this study was to determine the effective mass, shock transmission time, and deformation characteristics of a mat during impacts using high-speed video and to improve the accuracy of measuring foot-mat contact forces during landing. For validation, the same variables need to be accurately assessed using accelerometer and force plate data. METHODS A 24-kg impactor with an attached accelerometer was dropped onto the sample mat from various heights. The surface deformation of the mat was recorded using high-speed video, and force data were obtained from a force plate beneath the mat. RESULTS The maximum vertical deformations were between 0.088 and 0.118 m, with corresponding volume deformation estimates ranging from 0.030 to 0.044 m3. The delay between accelerometer and force plate readings at initial contact was approximately 7 ms. The delay between peak acceleration and peak force was 3 ms. The peak acceleration calculated from the video data was within 2.5% of that recorded via the accelerometer. The effective mass of the mat being accelerated corresponded to forces that ranged from 481 to 930 N, up to 12% of the peak force. CONCLUSIONS The acceleration estimates obtained from high-speed video were combined with the effective mass estimates from the volume calculation to give peak calculated forces at the bottom of the mat to within -1.1 to +3.7% of the force recorded via the force plate. The use of high-speed video can be used to give data of sufficient accuracy for measuring foot/mat contact forces in gymnastics landings.