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

Introduction: Landing mats that undergo a large amount of area deformation are now essential for the safe completion of landings from dismounts and vaults in gymnastics. The aim of this paper is to determine the effective mass, shock transmission time and deformation characteristics of a mat during impacts using high-speed video and hence improve the accuracy of measuring foot / mat contact forces during landing. To this end the same variables need to be accurately assessed using accelerometer and force plate data so that the high-speed video method can be validated. 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: Impact velocities ranged from 4.3 ms-1 to 6.5 ms-1 resulting in maximum vertical deformations between 0.088 m and 0.118 m with corresponding volume deformation estimates ranging from 0.030 m3 to 0.044 m3. The delay between accelerometer and force plate readings at initial contact was approximately 7 ms whereas 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 a force that ranged from 481 N to 930 N and this cannot be ignored as it accounts for up to 12 % of the peak force. Conclusions: The acceleration estimates obtained from the 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.