Taekwondo is a dynamic physical contact martial arts sport that requires quick reactions, agility, and explosiveness due to pressure and repetitive lower extremity movements in training and competition (Naserpour et al., 2021; Shin & Kim, 2020). The demands of sports with specific positions can lead to differences in the limbs and lengths of the dominant limbs in kicking and punching, which allows for power (Fox et al., 2023; Guan et al., 2021). This factor can be caused by pressure or use on one part (either right or left) of the body excessively and continuously (Zein & Sudarko, 2020).

In the lower extremities, as much as 44.5% (Pieter et al., 2012) and the hamstring was the most commonly injured muscle group (48.4%) compared to the quadriceps (23.2%) and calf muscles (9.6%) (Rüther et al., 2021). Non-contact ankle ligament injuries were more common (83%), and there were biomechanical differences in the knee joint between male and female athletes that contributed to the risk of non-contact ACL injuries (Willauschus et al., 2021; Zheng et al., 2020). The causes of lower extremity injuries are low muscle strength, incorrect technique, lack of flexibility, and inadequate injury rehabilitation (Fredriksen et al., 2020).

Recent research by Uh et al. (2024) discussed the demands of muscle strength, including the important role of hamstring muscles in taekwondo competition, so that muscle endurance can improve the performance of fast and powerful kicks. Other studies have suggested that asymmetry in hamstring strength ratios between the dominant and non-dominant legs may influence the risk of non-contact injuries. The main findings of this study indicate that hamstring strength in the dominant leg is significantly greater than in the non-dominant leg, particularly during eccentric contractions (Cheon et al., 2024; Kotsifaki et al., 2022).

With the increased participation of women in sports comes an increase in injury rates and a high risk of ACL injury of 4 - 6 times greater than men (O'Sullivan & Tanaka, 2021). Physiologically, the Q-angle in women tends to be larger because they have wider pelvises and shorter femurs. A larger Q-angle increases the range of motion and load on the patella joint, potentially increasing the risk of injury (Febiolita Tambunan et al., 2021). Thus, injuries can end an athlete's career, and injury recovery takes at least two months before the athlete can return to sport (Cha & Park, 2021; Minghelli et al., 2020). So, in this case, there are strong body parts and vice versa.

Although various studies have evaluated the hamstring to quadriceps strength ratio (H/Q ratio) in taekwondo athletes, most emphasized isokinetic ratios at various angular velocities among male and female athletes in general (Jung et al., 2017), as well as measuring asymmetry in young athletes without focusing on unilateral eccentric contractions (Jung et al., 2024), however, these studies did not specifically examine iconic hamstring eccentric strength in female taekwondo athletes from the Indonesian region, as well as the asymmetry profile between dominant and non-dominant legs when using practical measurements such as the Nordic hamstring test. Significantly, few studies have utilized portable devices and directly examined hamstring eccentric asymmetry values in female taekwondo athletes, even though this condition is highly relevant for identifying injury risk and designing appropriate training interventions.

Testing asymmetrical hamstring strength is essential for assessing maximum strength and potential imbalances, especially for athletes and individuals at risk of hamstring injuries (Claudino et al., 2021). Taekwondo athletes with hamstring muscle strength and a small imbalance value will produce techniques and movements that minimize injury. This study aimed to determine the profile of hamstring muscle eccentric strength in East Java female Taekwondo athletes. Therefore, the findings of this study are expected to contribute to the development of evidence-based training and rehabilitation programs by providing a specific profile of eccentric hamstring strength and asymmetry in sub-elite female taekwondo athletes. These insights can help coaches, trainers, and medical professionals identify muscle imbalances early and design targeted interventions that reduce the risk of lower extremity injuries and significantly enhance performance, instilling a sense of optimism and motivation in the athletes.

The research results on average left leg hamstring muscle strength in East Java female taekwondo athletes were 227.59 N of hamstring muscle strength in the left leg, with the highest strength of 364.75 N and the lowest value of 152.5 N. Meanwhile, the average right leg muscle was 271.31 N, with the highest strength of 341.25 N and the lowest strength value of 133.5 N. Hamstring muscles have an important role in supporting performance in daily activities such as walking and jumping (Ragia et al., 2021).

In addition to hamstring muscle strength, muscle imbalance is one of the risks of muscle injury. The study obtained an average imbalance of -4.5%, with the worst imbalance value of -19.9% on the left leg and an imbalance value of 10.3% on the right leg. At the same time, the best imbalance value is -2% on the left leg and 0.1% on the right leg. Muscle strength imbalance can adversely affect athlete performance and is a relevant factor in determining playing conditions that significantly limit player performance (Śliwowski et al., 2024). Muscle imbalance can be said to be good if the percentage of imbalance deficits in a person is less than 10%-15% (Silvers-Granelli et al., 2021), and currently, lower extremity strength asymmetry involving contact sports is a significant subject in several studies (Ryu & Lee, 2021).

The results of this study obtained several categories of hamstring strength using the Nordic hamstring formula. Table 3 shows the test results of East Java female taekwondo athletes. The analysis based on the Nordic hamstring formula shows differences in strength between the left and right limbs. Based on the analysis results in Table 4, the average hamstring eccentric strength of East Java taekwondo female athletes is 87% of the ideal target calculated based on the Nordic Hamstring formula. This value is still below the optimal threshold, so an overall increase in hamstring muscle strength of about 13% is needed. Specifically, the left leg requires an increase of about 10%, and the right leg about 15% to reach the ideal eccentric strength standard. In addition, the data also showed a tendency for strength dominance in the left leg, which could lead to muscle imbalances and increase the risk of injury. Therefore, bilaterally and unilaterally focused exercise interventions are recommended to improve overall muscle strength and balance.

This research aligns with previous research, which reported significantly higher strength levels on the dominant and non-dominant sides (Cheon et al., 2024). In that study, the dominant hamstring strength of young Korean taekwondo athletes was significantly higher than the non-dominant strength, especially during eccentric contraction.

Although this study focused on hamstring muscle eccentric strength and asymmetry between limbs, several other factors could influence the results but have not been analyzed in depth. Age is one variable that can affect muscle contraction capacity, as muscle mass and strength typically increase into early adulthood and then gradually decline (Shur et al., 2021). In this study, the age range of athletes was quite wide (14-22 years), potentially leading to physiological differences and muscle performance between age subgroups. In addition, training level or training experience also affects neuromuscular adaptation to eccentric loading, where athletes who train more intensely or longer tend to have higher and more stable muscle strength (Edouard et al., 2018). The technique of performing the Nordic hamstring test can also affect the accuracy of the results, especially if the athlete is unfamiliar with the testing procedure or does not perform the contraction to its full potential (van Dyk et al., 2019). Therefore, differences in results between individuals in this study may also be influenced by variations in age, training experience, and consistency of technique during testing, which should be considered in data interpretation and subsequent intervention design.

The findings indicate a notable imbalance in eccentric hamstring strength between limbs among sub-elite female taekwondo athletes, who tend to rely more on one leg. This asymmetry underscores the importance of targeted interventions to enhance muscular balance, particularly in the hamstring group, which is critical in maintaining postural stability and reducing injury risk. Implementing structured training strategies that focus on bilateral strength development is essential to support athletic performance and prevent potential injuries. Coaches and physiotherapists are vital in designing and supervising these programs, ensuring athletes achieve optimal physical condition while minimizing the likelihood of hamstring-related injuries.

The research team would like to thank the Binpres Taekwondo East Java, which has allowed its athletes to participate in this study.

All data supporting the findings in this study are available and accessible upon reasonable request to the corresponding authors. Data were collected and analyzed by ethical research standards and stored securely by the research team to ensure the confidentiality and integrity of the information.

This research does not receive external funding.

The author declares that this research is free from conflicts of interest with any party.