Key result
The largest increases in knee extension and flexion torques and thigh muscle volume were observed between the U15 and U18 age groups, with predominant development of knee flexor muscles after late adolescence.
Cross-Sectional
In elite soccer players, the most significant development in knee strength and thigh muscle volume occurs between late adolescence (U18) and early adulthood (U21), highlighting the importance of muscle hypertrophy and neuromuscular adaptation during this transition.
May guide age-specific training in elite youth soccer; leaves open longitudinal effects on performance or injury.
The purpose of the study was to describe age-related changes in knee strength and thigh muscle volume on elite soccer players from late adolescence to adulthood. Totally 191 soccer player participated in the study and were divided into 5 age groups, i.e. under 16 (U15), 17 (U16), 19 (U18), and 22 (U21) yrs and over 22 (O22) yrs. All of U21 and O22 subjects were professional soccer players. Maximal knee extension (KE) and flexion (KF) concentric torque were measured using isokinetic dynamometer at velocities of 1.05, 3.14, and 7.85 rad/s in both of the dominant and non-dominant legs. Femur length and cross-sectional areas of the quadriceps femoris and hamstrings at the upper, middle, and lower range of the thigh were determined by magnetic resonance imaging, from which the volume of quadriceps femoris (esQF) and hamstrings (esHAM) were estimated. From U15 to U18 neither KE nor KF at 1.05 rad/s increased significantly, although those at the other faster velocities increased significantly regardless of whether the data were expressed as absolute or adjusted value to body weight. In addition, esQF and esHAM also did not increase significantly from U15 to U18. However, the largest increases were observed between U18 and U21 in KE and KF at all the velocities as well as esQF and esHAM. Furthermore, when KE and KF were divided to esQF and esHAM respectively, the values also increased significantly from U15 to U21, suggesting higher knee strength in the professional soccer players were attributed to the concomitant development of thigh muscle volume with the increased neural activation. The ratio of KF to KE and the ratio of esHam to esQF increased slightly from U15 to O22, indicating the predominant development of knee flexor muscles on soccer players after late adolescence. The data presented in this study implied that increasing knee strength with emphasis on both thigh muscle hypertrophy and adaptation of neuromuscular function was essential for younger players to achieve higher soccer playing standards.
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Hoshikawa et al. (2007) conducted a cross-sectional in Healthy soccer players. Age vs. Younger age groups was evaluated on Maximal knee extension and flexion concentric torque and thigh muscle volume. The largest increases in knee extension and flexion torques and thigh muscle volume were observed between the U15 and U18 age groups, with predominant development of knee flexor muscles after late adolescence.
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