Relationships between knee muscle strength and functional performance in professional soccer players.

Introduction: Functional tests such as the Modified Star Excursion Balance Test (mSEBT), hop tests, and jump tests are widely used to monitor performance, neuromuscular function, and readiness in soccer players; however, their relationship with knee muscle strength remains unclear. Methods: This cross-sectional study investigated the associations between commonly used functional test outcomes and isokinetic quadriceps and hamstrings peak torque at 60°/s in professional male soccer players. Forty asymptomatic athletes completed the functional test battery, and isokinetic data were available for 38 players. The assessment included the mSEBT, single-leg hop for distance, bilateral hop, bilateral vertical jump, and single-leg vertical jump. Concentric isokinetic peak torque of the quadriceps and hamstrings was assessed at 60°/s using a Biodex System 4 dynamometer. Limb Symmetry Indices were calculated for strength and functional measures. Results: Bilateral vertical jump height showed moderate correlations with quadriceps peak torque, whereas single-leg vertical jump performance showed weak, side-specific associations with right hamstrings torque and left quadriceps torque. No meaningful correlations were found between single-leg hop performance and knee muscle strength. Strong inter-limb associations were observed for the mSEBT and single-leg hop test, but these tests were not significantly associated with one another. Functional symmetry indices were high, although they were not associated with quadriceps strength symmetry. Discussion: These findings indicate that functional tests reflect distinct neuromuscular attributes and should not be considered interchangeable with isolated measures of knee muscle strength. Therefore, return-to-sport and performance-monitoring decisions should integrate task-specific functional testing with objective strength assessment.