The relative force in squat jump is the best laboratory predictor of sprint performance in adolescent soccer players

Purpose
The aim was to determine the relationships between linear sprint performance and different outcomes relating to isokinetic strength, jump performance, and intermittent Wingate test performance in well-trained young (U19) soccer players.

Methods
The total of 18 elite male soccer players (age: 17.6 ± 0.8 years; body mass: 73.3 ± 5.9 kg, height: 180.8 ± 4.8 cm) performed a 20-m sprint test, countermovement jump, squat jump (SqJ), isokinetic measurement of knee flexors and extensors strength, and intermittent anaerobic test on a bicycle ergometer (IAnTB E10×6s with a 30-s rest interval). The strength and power outcomes of laboratory tests served as possible predictors of sprint performance in multiple regression analyses.

Results
The correlation analyses showed a significant relationship between all sprint lengths and relative maximum force measured by SqJ (r value: from –0.48 to –0.67) and between all sprint lengths and peak power (PP) measured by IAnTB E10×6s (r value: from –0.47 to –0.55). The average power measured by IAnTB E10×6s was associated with sprint lengths of 10, 15, and 20 m (r value: from –0.45 to –0.49). The SqJ predicted the 5-m sprint (R = 0.48; R2 = 0.18) and 10-m sprint (R = 0.55; R2 = 0.26). The PP together with the relative force (RF) predicted the 15-m (R = 0.65; R2 = 0.51) and 20-m (R = 0.77; R2 = 0.64) sprint performance.

Conclusions
The RF in SqJ can be used as a parameter relevant to linear 5-m, 10-m, 15-m, and 20-m sprint. Together with PP, it can be applied as a parameter relevant to linear 15-m and 20-m sprint.