Reliability and measurement of inter-limb asymmetries in four unilateral jump tests in elite youth female soccer players

Purpose: The purpose of this study was to determine the within and between-session reliability, and inter-limb asymmetries, in four unilateral jump tests in elite youth female soccer players. Given the low plyometric training age and paucity of data for this population, this research study was warranted. Methods: Nineteen elite youth female soccer players (age: 10 ± 1.1 years; height: 141 ± 7.9 cm; body mass: 35 ± 7.1 kg) were recruited from an elite Tier 1 Regional Talent Centre of a professional soccer club. Tests included the single leg countermovement jump (SLCMJ), single leg hop, triple hop, and crossover hops for distance with reliability quantified via the coefficient of variation (CV), intraclass correlation coefficient (ICC), and standard error of the measurement (SEM). Inter-limb asymmetries were also calculated. Results: Both test sessions resulted in excellent within-session reliability (ICC range = 0.81-0.99; SEM range = 0.11-0.49; and CV range = 2.6-6.0%). Between-session reliability was deemed good to excellent (ICC range = 0.72-0.99 and pooled CV = 2.7-5.7%). Asymmetries were deemed small across both test sessions with the highest value reported in the SLCMJ (6.12%). Conclusion: Results highlight that unilateral jump tests can be considered a reliable test protocol in elite youth female soccer players, which is important considering youth athletes likely do not have a vast plyometric training age. Furthermore, inter-limb differences appear small in the present sample which may also be explained by their limited training age, given that asymmetries have previously been highlighted to be a product of limb function over time