###### Abstract  
This study aimed to examine the relationship between the eccentric utilization ratio (EUR) and sprint, change of direction (COD), change of direction deficit (COD%), and vertical jump performance, including countermovement jump (CM) and squat jump (S). A total of 32 elite athletes (16 women and 16 men) participated. Performance was evaluated using force platforms and photocell timing systems during CMJ, SJ, 30 m sprint, and Pro-Agility tests. Pearson correlation and simple linear regression analyses were used to assess the relationships between EUR and performance variables. The results revealed that EUR was significantly associated with CMJ height (r = 0.587, \(p\) = 0.017) and 0-10 m sprint performance (r = 0.516, \(p\) = 0.041) in female athletes, whereas no significant relationships were found in males (r < 0.20, \(p\) > 0.05) for all performance variables. In contrast, strength-power metrics such as eccentric peak power (ECCPP), eccentric mean power (ECCMP), concentric mean power (CONMP), and peak power (PP) showed stronger associations with all performance variables, including COD, sprint segments, and jump tests. In conclusion, although EUR demonstrated limited predictive value particularly in male athletes directly measured strength-power variables appear to be more reliable indicators of athletic performance. These findings highlight the importance of prioritizing eccentric and concentric power outputs in performance assessment and individualized training strategies. eccentric utilization ratio; sprint ability; COD performance; lower body Power; sex differences; force metrics 22 May 202529 June 2  
fiber transition) and structural changes within the muscle-tendon complex. Although these changes are difficult to measure directly, they can be indirectly observed through field-based performance tests such as jump height, sprint velocity, and change of direction time [2,3]. Thus, these tests are not only indicators of performance but also useful tools for monitoring physiological adaptations in applied settings. Although vertical jump tests provide useful information, conventional outcome measures (e.g., jump height, peak power) offer limited insight, thus requiring a more detailed analytical approach [10]. Prior studies have proposed various calculations--such as pre-stretch augmentation percentage (PSAP), eccentric utilization ratio (EUR), and reactive strength index (RSI)--to indirectly assess an athlete's ability to utilize the SSC to improve jump height (JH) and peak power (PP) during CM] [1,2,11]. These indices have also been used to reflect dynamic performance capacity [1] or to monitor athletes' responses to different phases of training throughout the season [2]. Once JH or PP is measured using SJ and CMJ tests, the subtle differences captured by PSAP, EUR, and RSI allow practitioners and sport scientists to evaluate the percentage, ratio, or absolute difference between the two jumps. On average, CMJ height is slightly greater than SJ height [9,12]. Studies have reported improvements ranging from 18-20% to 20-30%, corresponding to a 2-4 cm difference in maximal JH [13, 14, 15]. [PERSON] and [PERSON] [16] attributed this difference to the storage and reutilization of elastic energy during CMJ, suggesting that a greater difference between CMJ and SJ indicates a superior capacity for elastic energy use. However, later studies questioned whether this difference results primarily from elastic energy mechanisms, proposing instead that the eccentric utilization ratio (EUR) more accurately reflects the effective use of the eccentric phase during CMJ. In line with these views, researchers have argued that a larger CMJ-S difference, as expressed by a higher EUR, may indicate a better capacity to utilize the eccentric phase [2]. Although EUR has been shown to be sensitive to training adaptations [2,17,18], few studies have directly examined its relationship with athletic performance [19,20]. Therefore, the utility of EUR as a performance indicator or a guide for training design remains uncertain.