Effect of maturity status on lower-limb strength testing reliability in academy football players from an elite professional club

Introduction: In top-level football, clubs seek to identify young talent. This identification requires using tests to notably evaluate the lower-limb strength, which is a decisive physical quality in football performance. However, the tests used are not always highly reliable to interpret results meaningfully, particularly among age categories since their reliability could differ according to maturity status (Ferrari et al., 2023). In addition, lower-limb strength testing reliability may also vary according to movements performed, whether these are mono- or poly-articular. In this sense, it is possible to suggest that pre-pubertal players exhibit lower scores of test-retest reliability during poly-articular movements than their older counterparts because of their poorer motor coordination due to immaturity of cerebellum. However, this remains to be further clarified. Therefore, the aim of this study was to examine the test-retest reliability of dominant lower-limb strength on abduction, adduction, anterior or posterior chain movements in football players from an elite professional club academy, and to compare the results depending on maturity status and movement performed. Our hypothesis is that strength testing reliability will be lower for pre-pubertal than pubertal and post-pubertal players, more particularly for poly- than mono-articular movements in pre-pubertal players. Methods: Seventy players from a professional club academy were recruited and divided into 3 groups : 24 pre-pubertal (Pre; 12.8±0.5 years, -1.9±0.5 years from Age at the Peak Height Velocity or APHV), 18 pubertal (Pub; 15.2±0.6 years, +0.3±0.5 years from APHV), and 28 post-pubertal (Post; 16.6±1.6 years, +2.4±1.1 years from APHV). After at least two familiarization sessions, they performed five maximum strength tests involving adductor, abductor, posterior or anterior chain muscles, each twice, one week apart. Intraclass correlation coefficient (ICC) and coefficient of variation (CV) were calculated for each test. Results: Most test-retest evaluations showed good statistical reliability for each group (CV<10% and ICC>0.90) (see Table below). However, the post-pubertal players systematically exhibited lower CV and higher ICC values than their pre-pubertal and pubertal counterparts. Discussion/Conclusion: Lower-limb strength testing reliability is influenced by the players’ maturity status, with pre-pubertal players showing higher CV and lower ICC than their older counterparts, notably for polyarticular movements involving posterior chain muscles in a standing position. Therefore, in young elite soccer players, lower-limb strength testing reliability is not interchangeable between age categories, and caution should be done when interpreting strength results for talent identification and long-term player development purposes. References Ferrari, A., Baquet, G., Blazevich, A. J., & Ratel, S. (2023). Influence of recovery time after warm-up on vertical jump performance in trained prepubertal and postpubertal male athletes. Journal of Strength and Conditioning Research, 37(10), 1985–1992. https://doi.org/10.1519/JSC.0000000000004487