Author(s): KOZINC, Ž., ŠARABON, N., Institution: UNIVERSITY OF PRIMORSKA, FACULTY OF HEALTH SCIENCES, IZOLA, Country: SLOVENIA, Abstract-ID: 946

INTRODUCTION:
The eccentric utilization ratio (EUR), defined as the difference between countermovement jump (CMJ) and squat jump (SJ) performance, has been traditionally linked to elastic energy use and stretch-shortening cycle efficiency [1]. However, recent theories suggest higher EUR may also reflect different factors, such as poor concentric rate of force development (RFD) [2], questioning its role as an indicator of athletic performance. The aim of this series of exploratory studies is to contribute to the understating of the mechanisms underlying the variation in the magnitude of the EUR.
METHODS:
The paper presents a series of exploratory analyses based on data available from previous confirmatory studies and data from authors’ database. In all cases, vertical jumps (CMJ and SJ) were performed on a Kistler force plate (model 9260AA6). Three repetitions of each jump with 1-min rests were performed with hands placed on the hips, and the repetition with best jump height was take for further analysis. Jump heights was calculated using take-off velocity method.
RESULTS:
In the largest exploratory study, we compared EUR across 9 different sports (total n = 712), showing little difference between sports characterized by jumping (e.g., volleyball, basketball) and others. In the second analysis (n = 314; runners, basketball and soccer players) inverse correlations emerged between EUR and RFD in SJ (r = –0.41; p < .001), when the former was calculated based on force parameters. A third analysis (n = 45, volleyball) revealed that CMJ metrics exhibit larger correlation to performance proxies (sprint, agility and approach jump tests) than EUR.
CONCLUSION:
The results of the presented exploratory analyses align with the current theory on mechanisms driving variations in EUR [2]. Greater height in CMJ is largely underpinned by the build-up of force and muscle activation during the countermovement. Our analysis suggests that the remaining variation in EUR among individuals may be explained by different factors, and that EUR is not necessarily linked to superior athletic performance. Notably, poor concentric RFD and lower muscle stiffness were suggested to be related to lower SJ performance, and consequently, higher EUR. However, it has to be stressed that further studies are needed to reach firmer conclusions, as our analysis were purely exploratory.

1. McGuigan MR, Doyle TLA, Newton M, Edwards DJ, Nimphius S, Newton RU. Eccentric utilization ratio: Effect of sport and phase of training. J Strength Cond Res. 2006;20(4):992–5.
2. Van Hooren B, Zolotarjova J. The Difference between Countermovement and Squat Jump Performances: A Review of Underlying Mechanisms with Practical Applications. J Strength Cond Res. 2017;31(7):2011–20.