Biomechanics research on laterality effect between dominant and non-dominant during double roundhouse kick in the competitive taekwondo

<bold>Background: </bold>The Double Roundhouse Kick (DRK) is one of the major scoring tools and athletes employ the leg of the dominant side (DS) or the non-dominant side (NS) for always attacking in an alternating state. The purpose is to examine the discrepancies in the biomechanical characteristics of the DS and NS of the leg of the DRK skills of sub-elite taekwondo athletes.<bold>Methods: </bold>Using the Vicon, Kistler, and Daedo brand Electronic Body Protector (EBP), collection of the DRK data (attack time, joint angle, joint angular velocity, joint moment, ground reaction force, etc.) of 12 sub-elite taekwondo athletes (19.6 +/- 2.0 yr, 180 +/- 7.3 cm, 70 +/- 9.8 kg) with the DS leg and NS leg. The measured data analyses via Visual3D, and statistical methods using nonparametric tests paired with samples based on the Wilcoxon signed-rank test (The significance level is set as significant for P<0.05, and very significant for P<0.01).<bold>Results: </bold>(i) There is no statistically significant discrepancy between the DS and NS at the time of hit (P>0.05) and shift of the center of gravity (P>0.05). (ii) Attacking leg (AL): the maximum knee flexion angle (Knee-MFA) (P<0.05) and the peak linear velocity of attack of the foot in the vertical hitting direction (P<0.01) on the DS was greater than that on the NS during the first hit phase (P1). (iii) Supporting leg (SL): the peak hip extension moment (P<0.05) on the DS was reported to be higher than that of the NS during the second hit phase (P2). (iv) Symmetry Index (SI): In the P1, the vertical ground reaction force (vGRF) of the SL leads to SI = 10.19 %, and in the P2, the vGRF of the SL results in SI = 18.48 %.<bold>Conclusions: </bold>The DRK requires more and more symmetry between the DS and NS. The Knee-MFA of the AL and the line of attack speed of the foot in the vertical striking direction of the SL exhibited significant discrepancies. The DS has higher striking speed, athletes need to improve the striking speed of the NS leg in training, achieving more scoring opportunities in the game. Both the DS and NS revealed strong symmetry in the peak SI of the ground reaction force of the SL stirrup; however, weak symmetry was attained in the peak SI of the vGRF of the SL landing cushion.