(52) DIFFERENCES IN COUNTERMOVEMENT JUMP CHARACTERISTICS IN

Purpose: The Isometric Mid-Thigh Pull (IMTP) is a well-established strength test that assesses whole-body force production in athletes, including rugby athletes (1). Lower-body power is crucial for rugby performance, influencing linear speed, change of direction, and impact absorption (3). However, differences in jumping characteristics between “strong” and “weak” rugby athletes as demarcated by IMTP strength have not been investigated.This study examines differences in CMJ characteristics (jump height, concentric impulse, eccentric rate of force development, & peak propulsive force) between "strong" and "weak" rugby athletes, categorized based on IMTP peak force (PF). Methods: Major league rugby athletes (n = 30) performed an IMTP to determine PF and were put into "strong" (n = 13, height = 188±5.6cm weight = 117.5±8.4kg, age=26.8±4.0, IMTP PF = 4881.6±489.6 N) and "weak" (n = 17, height = 183.8±7.1cm, weight = 96.8±9.5kg, age=27.5±4.1 y, IMTP PF = 3985.1±348.6) groups based on their proximity to the median. CMJ performance was assessed using force plates sampling at 1000 hz to measure jump height (JH) (cm), concentric impulse (CI) (Ns), eccentric rate of force development (eRFD) (kN/s), and peak propulsive force (PPF) (N). Welch’s t-test assessed group differences (a= 0.05). Data were reported as raw values, scaled to body weight, and as z-scores. Results: Stronger athletes demonstrated significantly greater CMJ CI (t= 5.54, p < 0.001), and CMJ PPF (t= 2.95, p= 0.007). CMJ JH was significantly lower in the strong group (t= -2.88, p= 0.009), while eRFD showed no significant difference (t= 0.49, p= 0.626). Conclusions: Stronger rugby athletes, based on IMTP PF, produced significantly greater CMJ CI and PPF, demonstrating superior force output during jumping. However, they recorded lower JH, suggesting that greater absolute strength does not necessarily translate to higher vertical displacement. eRFD showed no significant difference between groups, indicating it may not be a key factor distinguishing isometric strength. These findings emphasize the need to look beyond JH when assessing lower-body power in rugby. Normative IMTP force data suggests PF ranges of 2254-3851 N for professionals (2). Yet, both the “strong” and “weak” groups were above this range, highlighting variability in force characteristics across playing levels. Variation in IMTP force across rugby populations highlights the importance of standardized testing protocols for better athlete comparison and development. Practical Applications: Strength coaches should take caution when prioritizing maximal force and impulse development over JH when assessing lower-body strength and power in rugby athletes. Normalizing CMJ and IMTP data to body weight or using z-scores can enhance athlete comparisons and training insights when absolute strength values are decoupled from dynamic performance outcomes. Future research should examine long-term strength and power adaptations regarding improving IMTP strength and its correlation with CMJ performance. Acknowledgements: None