Isokinetic Knee Strength and Multidirectional Jump-Landing Asymmetry in Professional Football Players After Anterior Cruciate Ligament Reconstruction: An Exploratory Cross-Sectional Study

Background/Objectives: Isokinetic testing is widely used after anterior cruciate ligament reconstruction (ACLR), but isolated knee strength may not reflect function during braking, re-acceleration, and stabilization. This study examined relationships between isokinetic strength and vertical and multidirectional performance in professional football players after ACLR and compared asymmetry across functional domains. Methods: Eleven male professional players, 12–40 months post-ACLR and back in unrestricted training and competition, completed isokinetic concentric knee extensor and flexor strength testing, single-leg countermovement and drop jumps, and unilateral and bilateral forward and lateral jumps on 3D force-plates. Limb differences, strength–performance associations, bilateral contributions, and domain-specific asymmetry were assessed. Results: No operated–non-operated limb difference remained significant after Holm correction. Knee extensor strength was positively associated with drop-jump reactive strength index (ρ = 0.612), countermovement-jump height (ρ = 0.491), anterior–posterior braking impulse during forward hop-in (ρ = 0.382), and propulsive impulse during forward hop-out (ρ = 0.442); however, none of the eight prespecified strength–performance correlations was statistically significant either before or after Holm adjustment. Median asymmetry differed across domains, reaching 20.9% for temporal control and stabilization and 14.7% for directional braking, compared with 9.9% for strength and 6.2% for vertical performance. Fifty percent of players had a median multidirectional-task asymmetry ≥20%. The operated limb contributed 49.9–53.0% of the total output during bilateral tasks. Conclusions: The absence of significant group-level differences in isokinetic strength and vertical jump outcomes did not exclude asymmetries in directional braking and stabilization. Isokinetic, vertical, and multidirectional assessments provide complementary, non-interchangeable information after ACLR. Multidirectional testing may therefore provide additional information on movement strategies that is not captured by strength and vertical jump tests alone.