Maintaining balance while performing “Hakdariseogi” in Taekwondo, which involves standing on one leg, is a critical aspect of the Poomsae competition. The purpose of this study was to investigate the effect of proprioceptive training and lower-limb muscular strength training on the balance of Taekwondo Poomsae athletes over a 6-week period. Thirty Taekwondo Poomsae athletes were randomly assigned to three groups, namely, a proprioception training group, a lower-limb muscular strength training group, and a control group. Biomechanics data were collected using eight infrared cameras (Qualysis, Sweden) at 200 Hz and a force plate (Kistler, Switzerland) at 2,000 Hz while the participants performed “Hakdariseogi” before and after the 6-week intervention. Balance and stability variables were calculated using customized MATLAB R2014b software (Mathworks, Inc., USA). The medio-lateral (M/L) center of pressure (CoP) range, M/L CoP mean velocity, antero-posterior (A/P) CoP range, A/P CoP mean velocity, and the vertical ground reaction torque after the training were reduced at P1 in the PG groups (p < 0.05). A decrease in the A/P CoP range, A/P CoP mean velocity, and vertical ground reaction torque after the training were observed at P2 in the PG and SG groups (p < 0.05). The PG exhibited a smaller A/P CoP range and A/P CoP mean velocity, in comparison to CG (p < 0.05). The A/P CoP position at P1 was negatively correlated with the vertical ground reaction torque, A/P CoP range, and A/P CoP mean velocity at P2(r = -0.438, r = -0.626, r = -0.638). Based on the above results, this study determined that both proprioception training and lower-extremity muscle strength training resulted in an improvement of athletic performance. It was also desirable to move the CoP position through conscious effort forward at P2 in order to maintain the crane stance without sway.