Background: Learning Taekwondo can contribute to the growth and physical fitness performance of children and adolescents. However, there is limited research on learning Taekwondo Poomsae. Therefore, this study aims to understand the impact of learning Taekwondo Poomsae on physical fitness performance. Purpose: The purpose of this study was to investigate the effects of 8 weeks of Taekwondo Poomsae training on lower limb explosive strength, reaction ability, and balance in junior high school adolescents. Methods: Sixteen male junior high school students with no prior sports experience or Taekwondo training were recruited. The participants were randomly assigned to either the experimental group (n = 8) (participating in school physical education classes plus Taekwondo Poomsae training) or the control group (n = 8) (participating only in school physical education classes). Both groups underwent an 8-week training program. Before and after the training, all participants underwent measurements of height, weight, leg length, dynamic balance ability, reaction ability, and lower limb explosive strength. The participants’ data were analyzed using a mixed-design two-factor analysis of variance to compare the differences in reaction ability and balance ability between the two groups. When the interaction effect was significant, post hoc comparisons were performed using the LSD method. Independent sample t-test was used to test the significance of improvement percentage between the experimental and control groups. Pearson correlation analysis was used to examine the relationship between lower limb balance ability and reaction ability. Results: The experimental group showed significant differences in explosive strength and balance performance compared to the control group (p < .05). Moreover, the improvement percentages in both explosive strength and balance performance were significantly different between the two groups (p < .05). However, there were no significant differences in reaction ability between groups or in the improvement percentage (p > .05). Before the training, there was a low correlation between reaction ability and balance performance (r = .352, p =.10). After the training, there was a moderate correlation between reaction ability and balance performance (r = .665, p < .05). Conclusion: Taekwondo Poomsae training can significantly improve lower limb explosive strength and balance in junior high school adolescents. The improvement in explosive strength, reaction ability, and balance performance was greater in the experimental group than the control group. The correlation between reaction ability and balance performance after training suggests that Taekwondo Poomsae training may enhance the students’ body coordination and sensory integration. Future studies could explore the differences in training and physical development across different Taekwondo training methods and age groups.