Relationship between reactive strength index variants in rugby league players

McMahon, JJ ORCID: https://orcid.org/0000-0001-9952-7846, Suchomel, TJ, Lake, JP and Comfort, P ORCID: https://orcid.org/0000-0002-1131-8626 2021, 'Relationship between reactive strength index variants in rugby league players' , Journal of Strength and Conditioning Research, 35 (1) , pp. 280-285.

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Abstract

Two reactive strength index (RSI) variants exist, the RSI and RSI modified (RSI_mod) which are typically calculated during the drop jump (DJ) and countermovement jump (CMJ), respectively. Both RSI variants have been used to monitor athletes’ ability to complete stretch-shortening cycle actions quickly, but they have never been compared. The purpose of this study was to determine if they yield relatable information about reactive strength characteristics. Male professional rugby league players (n = 21, age = 20.8±2.3 years, height = 1.82±0.06 m and body mass = 94.3±8.4 kg) performed three DJs (30 cm) and CMJs on a force plate. RSI and RSI_mod were subsequently calculated by dividing jump height by ground contact time (GCT) and time to take-off (TTT), respectively. All variables were highly reliable (intraclass correlation coefficient ≥0.78) with acceptable levels of variability (coefficient of variation ≤8.2%), albeit larger variability was noted for DJ variables. Moreover, there was a large relationship between RSI and RSI_mod (r=0.524, P=0.007), whereas very large relationships were noted between jump heights (r=0.762, P<0.001) and between GCT and TTT (ρ=0.705, P<0.001). Additionally, RSI (0.90±0.22) was largely and significantly (d=2.57, P<0.001) greater than RSI_mod (0.47±0.08). The DJ-derived RSI yields much larger values than the CMJ-derived RSI_mod and although a large relationship was noted between them, it equated to just 22% shared variance. These results suggest that the two RSI variants do not explain each other well, indicating that they do not assess entirely the same reactive strength qualities and should not be used interchangeably.

Item Type:	Article
Schools:	Schools > School of Health and Society > Centre for Health Sciences Research
Journal or Publication Title:	Journal of Strength and Conditioning Research
Publisher:	Lippincott, Williams & Wilkins
ISSN:	1064-8011
Related URLs:	Publication
Depositing User:	Dr John J McMahon
Date Deposited:	11 Apr 2018 09:09
Last Modified:	15 Feb 2022 23:07
URI:	https://usir.salford.ac.uk/id/eprint/46674

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