Assessment of Lower Limb Asymmetry in Elite U16 Football Players Using Jump Tests and Kineo Technology

Abstract

Inter-limb asymmetry is recognized as a key factor influencing performance and injury risk in elite youth football. This study aimed to assess lower limb asymmetry in U16 players using vertical jump tests—Squat Jump (SJ) and Countermovement Jump (CMJ)—and isokinetic assessments via the Kineo Intelligent Load system. Eighteen elite U16 male players (age 15.9±0.3 years) performed SJ and CMJ tests on a contact platform, with the Elasticity Index (EI) calculated. Isokinetic tests (leg extension and curl) at 60°/s and 300°/s were conducted using Kineo. Asymmetry was determined for each variable using standard formulas, with >10% considered clinically significant. Paired t-tests and correlation analyses compared limbs and explored links between strength and jump performance. No significant group-level differences between limbs were found (p>0.05), but several players exceeded the clinical threshold, especially in hamstring strength. EI values fell within normal reference ranges (≈15–25%) and correlated moderately with isokinetic strength at certain velocities (e.g., r=0.51 for leg extension at 60°/s). Correlations between jump height and absolute strength were weak (r=-0.15 to 0.13), indicating the multifactorial nature of jump performance. Combining jump and isokinetic testing provides valuable insights into asymmetry and neuromuscular function. While no significant group-level asymmetries were observed, several players exceeded the clinical threshold, particularly in hamstring strength, highlighting the need for individualized monitoring to prevent injuries and guide performance training.