Abstract
Introduction. The lack of research on fencing in Indonesia and the absence of analysis on muscle activation in the lower leg muscles, especially the quadriceps muscles, during fencing movements, such as lunges, is a significant gap in the existing literature. This knowledge gap is especially pronounced for athletes with knee pain and quadriceps angle differences. Knee pain causes athletes to experience a decrease in performance, one of which is caused by a decrease in balance. Purpose: This study aims to determine the difference in balance in athletes with knee pain and without knee pain and to determine the activation of the rectus femoris muscle, vastus medialis muscle, and vastus lateralis muscle in the lunge movement in athletes participating in fencing with sable and floret numbers. in the Fencing Sports Activity Unit at Tunas Pembangunan University (UTP) Surakarta. Methods. A descriptive and analytical observational research design was employed for this cross-sectional study, using purposive sampling to recruit seven fencing athletes of UTP. Stork balance test was used to check the balance score and surface electromyography records were used to collect data, and the data analysis was conducted using the nonparametric Mann-Whitney U test. Results. The results of this study prove that the body balance scores of athletes who have complaints of knee pain are significantly worse (p < 0.05) compared to fencers who do not have complaints of knee pain. Knee pain also significantly reduced the activation of the rectus femoris, vastus medialis, and vastus lateralis muscles (p < 0.05). Conclusion. Based on the results and discussion above, knee pain significantly decreases body balance and quadriceps muscle activity.

Keywords
knee pain, body balance, quadriceps, muscle activity, electromyography