Handball is a very popular competitive sport today and has been quite popular in Indonesia. It is played in several regional and international competitions (Muarif et al., 2024). Depending on their position, each player has different physical demands, including explosive movements such as jumps, sprints, and quick direction changes, all of which require excellent strength and endurance. Therefore, handball is categorized as a sport with a high potential for injury, especially in the lower extremities (Firmansyah et al., 2024). In handball athletes playing in the Iceland league, the majority of injuries were to the lower extremities, particularly the knee (26%) and ankle (19%) (Rafnsson et al., 2019). Knee injuries, particularly anterior cruciate ligament (ACL) ruptures, are the most common serious injuries in individuals aged 15–19 years. Girls are at higher risk for ACL injuries, especially during adolescence (Schmidt & Jaitner, 2023).

The causes of injuries to the lower extremities of handball athletes are rapid changes in direction, sudden landings from jumps, and frequent contact and collisions between players (Raya-González et al., 2022). In addition, risk factors for injury also include weak muscle strength, improper technique, limited muscle flexibility, and a suboptimal injury rehabilitation process (Fredriksen et al., 2020).

The hamstring muscle group is particularly crucial for activities such as acceleration, deceleration, and changing direction, where athletes often need to balance on one leg (Wing et al., 2020). Hamstring muscles play an important role in performance and injury prevention for handball athletes. Therefore, hamstring strength tests are important for athletes and coaches to understand hamstring muscle strength and its related normative data, and it is also important to design the right training program when evaluating rehabilitation progression and making return-to-play decisions (Firmansyah et al., 2024). In addition, normative data on hamstring muscle strength is essential for medical doctors and physical therapists to assess athletes' physical condition, determine their readiness, and ensure safety when they are ready to return to competition after injury. This data assists in evidence-based decision-making for rehabilitation and prevention (Owoeye et al., 2024).

Four assessments of eccentric hamstring muscle strength with knee flexors often used to determine imbalance are carried out using the Nordic hamstring test (Van Dyk et al., 2019). Testing eccentric hamstring strength is crucial for assessing maximum strength and potential imbalances, especially for athletes and individuals at risk for hamstring injuries (Claudino et al., 2021). Eccentric strength assessment is more appropriate than isokinetic testing (Chavarro-Nieto et al., 2022). Several instruments are available to assess hamstring muscle strength, and eccentric strength assessment is helpful as an indicator for predicting injury, one of which is using the Nordic hamstring test (Timmins, 2016; Opar., 2015; Barrera-dom et al., 2021). Handball athletes with balanced hamstring muscle strength, indicated by low asymmetry values, tend to be able to perform techniques and movements more effectively. Good hamstring muscle balance not only improves athlete performance but also contributes to reducing the risk of injury. With optimal hamstring muscle strength, athletes can maintain stability and flexibility, which are very important in carrying out various techniques in handball. This study aimed to determine the strength and asymmetry of the hamstring muscles in female handball athletes in Surabaya City.

Although many studies highlight the importance of hamstring muscle strength in preventing injury in handball athletes, data on the strength profile and asymmetry of hamstring muscles in female handball athletes is still limited. This study is important because it provides an empirical picture specific to the local population, which has not been widely explored in national and international literature. The results are expected to be a reference in developing evidence-based training programs and appropriate rehabilitation protocols while helping coaches and medical professionals identify and address muscle asymmetries at risk of increasing injury.

The research results displayed through Table 1 to Table 7 and Figure 1 to Figure 3 provide a comprehensive picture of eccentric strength and hamstring muscle asymmetry in female handball athletes in Surabaya City. Table 1 presents descriptive statistics showing that the average right and left hamstring muscle strengths are 230.70 N and 233.61 N, respectively, with an average asymmetry value of -1.44%, indicating a relatively balanced muscle condition. Figure 1 reinforces this data by visualizing the variation in strength between individuals.

The frequency distribution of hamstring muscle strength is shown in Table 2 and Table 3, where the left muscle strength is more concentrated in the 178-221 N range, while the right strength is more spread out.

The results showed a significant variation in hamstring muscle strength in female handball athletes in Surabaya City. The average hamstring strength of the left leg reached 233.6 N, with the highest value of 340.75 N and the lowest 177.75 N, while the right leg had an average of 230 N, with the highest value of 319.75 N and the lowest 143.25 N. This difference indicates an imbalance of strength between athletes, even between limbs in one athlete. The proportion of athletes with strength below the average value is quite large, indicating that some athletes have not reached the optimal strength standard required to support performance and prevent injury. This underscores the importance of a training program focused on improving hamstring strength, especially for athletes with low strength values, to reduce the risk of injury and improve knee joint stability during competitive activities. The hamstring muscles are crucial in controlling daily body movements, playing a role in basic activities such as walking and running, as well as complex activities such as jumping and maintaining posture when sitting or standing (Paramita, Rahmanto, & Rahim, 2024).

In addition to hamstring muscle strength values, muscle asymmetry is an important factor affecting injury risk. The results showed that the lowest asymmetry value was -2.5% in the left leg and 0.4% in the right leg, while the highest asymmetry reached -19.4% in the left leg and 13.3% in the right leg. This significant difference in asymmetry indicates a muscle imbalance that can potentially increase the risk of injury, given that Silvers-Granelli et al. (2021) stated that the risk of injury increases if the strength deficit between sides exceeds 10-15%. However, on average, the asymmetry in Surabaya City female handball athletes is only 1.4%, far below the international normative limit of 6.8% for ages 20-30 years (Vald Performance), which indicates a relatively balanced muscle condition and supports optimal performance (Hammi, 2018).

The asymmetry imbalance found in some athletes is likely due to the dominance of certain limbs, where athletes tend to use one leg more often as a fulcrum or dominant leg in movements such as kicking, jumping, or changing direction. In addition, uneven training loads or a lack of unilateral strengthening exercises may exacerbate this imbalance. Therefore, coaches need to identify athletes with high asymmetry and design training programs that target the strengthening of weaker limbs to reduce the risk of injury and improve athletes' stability and overall performance.

The results showed that most female handball athletes in Surabaya City had not reached the ideal hamstring muscle strength category based on the Nordic Hamstring formula (N = 4 x body mass (kg) + 26). The average percentage of hamstring strength of all athletes only reached 88.1%, with details of 88.7% on the left leg and 87.6% on the right leg. This indicates an overall need for improvement in hamstring muscle strength of approximately 11.9%, with a slightly greater improvement in the right leg (12.4%) than the left leg (11.3%). Nonetheless, these results must be interpreted with caution, given the several limitations of this study. First, the relatively small sample size may limit the generalizability of the findings to a broader population of female handball athletes. In addition, strength measurements using the Nordic Hamstring Test are potentially subject to bias due to variability in execution techniques and athletes' motivation levels at the time of testing, which may affect the accuracy of the results. Geographical limitations are also important because the training conditions, coaching patterns, and characteristics of athletes in Surabaya may differ from those of other regions, so these results are not necessarily representative of athletes from other regions.

A study with a larger and geographically diverse sample is recommended for future research to increase external validity. In addition, exploration of biomechanical factors that influence hamstring muscle strength and asymmetry, such as movement patterns, posture, and jumping technique, may provide further insight. Longitudinal studies are also highly recommended to monitor the development of muscle strength and injury risk over time, especially the training program implemented. With such an approach, training interventions can be better targeted to improve hamstring muscle strength and flexibility, which in turn can reduce injury risk and improve overall athlete performance; some exercise models that can be used to increase hamstring muscle strength and flexibility include:

This study confirms that most Surabaya City female handball athletes have not achieved ideal hamstring muscle eccentric strength based on the Nordic Hamstring formula (N = 4 x body mass (Kg) + 26), with an average overall strength of only 88.1%. The average strength of the left and right limbs was 88.7% and 87.6%, respectively, indicating the need for increased strength on both sides—the asymmetry assessment of female handball athletes in Surabaya City with an overall average of 1.4%. Ten female handball athletes in Surabaya City have an asymmetry value below 10%; these results make it perfect for athletes towards peak performance. A small number of athletes with asymmetries above 10% signal the need for unilateral specialized training interventions to address these imbalances. These findings provide important input for coaches and athletes to focus on training programs that target improvements in hamstring muscle strength and balance to optimize performance and prevent injury risk.

Future research is recommended to develop variables that have not been explored, such as biomechanical factors or injury history. Expansion of subjects and data collection to make the sample more representative is also important. In addition, future research should consider gender differences by including male athletes and comparing athletes with different skill levels (e.g., elite athletes) for a more comprehensive understanding.

The researcher would like to thank all the participants who helped complete this research project.

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