Seasonal Associations Between Isometric Strength and Dynamic Performance in Elite Youth Soccer Players

To investigate within-player, longitudinal associations between global and hip-specific isometric strength and dynamic performance across a season in elite youth soccer players.

In a repeated-measures observational design, 25 elite U19 male soccer players were assessed at preseason, midseason, and end of season. Global isometric strength was evaluated using the isometric mid-thigh pull (IMTP), while hip adduction and abduction strength were assessed via fixed-frame dynamometry. Dynamic assessments included the countermovement jump (CMJ), single-leg CMJ, linear sprinting (5-30 m), 505 test, and Bronco test. Within-player associations were examined using repeated-measures correlation, accounting for the nonindependence of repeated observations.

Increases in IMTP absolute and relative peak force were associated with improvements in CMJ jump height and peak power (rrm = .50 to .62) and faster 505 change of direction time (rrm = -.32 to -.44). No meaningful associations were observed between IMTP strength and unilateral jumping, linear sprinting, change of direction deficit, or endurance performance. Changes in isometric hip abduction strength were associated with CMJ performance (rrm = .28 to .53) and 505 change of direction time (rrm = -.29 to -.41), whereas isometric hip adduction strength showed no significant associations with any dynamic outcomes.

Longitudinal changes in isometric strength were most strongly associated with dynamic tasks sharing similar biomechanical and kinetic demands, particularly those requiring high vertical or braking force production. These findings reinforce isometric testing as a low-fatigue indicator of force capacity and robustness, while indicating that such measures should complement, rather than replace, dynamic assessments within a comprehensive performance monitoring framework.