The Relationship Between Reactive Strength Index, Eccentric Utilization Ratio, Pre-Stretch Augmentation Percentage and Leg Stiffness in Elite Female Volleyball Players: Correlational Research

Objective: This study examined the relationships between Reactive Strength Index, leg stiffness, eccentric utilization ratio, and pre-stretch augmentation percentage in elite female volleyball players. Material and Methods: Fourteen athletes performed squat jump, countermovement jump, and drop jump tests over 3 measurement days. An optical measurement system was used to assess ground reaction forces. Data normality was assessed using the Shapiro-Wilk test. Pearson's correlation was applied to normally distributed variables, while Spearman's correlation was used for non-normally distributed variables. Statistical significance level was determined as p<0.05. Results: Reactive Strength Index showed a strong positive correlation with leg stiffness (r=0.931, p<0.001) but had no significant relationship with eccentric utilization ratio and pre-stretch augmentation percentage. A strong positive correlation was observed between eccentric utilization ratio and pre-stretch augmentation percentage (r=0.985, p<0.001), suggesting that they are interdependence. Weak negative correlations were found between leg stiffness and both pre-stretch augmentation percentage and eccentric utilization ratio. Conclusion: These findings highlight the strong link between Reactive Strength Index and leg stiffness in jump mechanics. The high correlation between pre-stretch augmentation percentage and eccentric utilization ratio suggests that they reflect similar aspects of tissue behavior during stretch-shortening cycle activities and provide insight into biomechanical factors influencing athletic performance.