Purpose: Lower-limb strength assessment is essential for talent identification, training program design, and return-to-play decisions. However, the influence of biological maturity on test reliability remains unclear, particularly in prepubertal players whose motor coordination is still developing. This study examined the test-retest reliability of dominant-limb abduction, adduction, and anterior and posterior chain tests in elite youth football players, and compared reliability across maturity stages and movement types. Methods: Seventy academy players were divided into 3 groups: 24 prepubertal, 18 pubertal, and 28 postpubertal. Following at least 2 familiarization sessions, players performed 5 maximal isometric strength tests on 2 occasions 1 week apart. The coefficient of variation (CV) and intraclass correlation coefficient (ICC) were calculated for each test, and statistical comparisons between maturity groups were performed using the Modified Signed-Likelihood Ratio Test (for CVs) and Fisher Z transformation (for ICCs). Results: Most tests demonstrated good to excellent reliability across all maturity levels (CV < 10%, ICC > .90). However, postpubertal players exhibited significantly lower CVs and higher ICCs than prepubertal players in several tests, particularly for polyarticular standing posterior chain movements (P < .05). No significant differences were observed between prepubertal and pubertal players. Conclusions: These results indicate that test reliability improves with biological maturity, likely due to enhanced motor coordination and movement control. Consequently, the reliability of lower-limb strength assessments is not interchangeable between maturity categories, and results should be interpreted with caution when used for talent identification or long-term player monitoring in elite youth football players.
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