Athlete development is considered a multi-factorial and dynamic overtime process. Thus, understanding what factors and behavioural activities contribute most to development is important. The present study examined longitudinal relationships between training time and maturity status with physical performance indices in youth volleyball players. Prospective mixed longitudinal tracking over 3 years. Participants were N = 78 selected male volleyball players, aged 11-15 years (M = 13.81, SD = 1.20 years) from N = 41 competitive Swiss clubs. Alongside coach-reported weekly training time, participants completed standardised anthropometric and physical performance tests (e.g., standing long jump [SLJ]; 9-3-6-3-9 agility sprint). Linear mixed models (LMM) examined longitudinal independent and interacting relationships between training time and maturity status (years from peak height velocity; PHV) with physical performance. For SLJ, both training time and maturity status explained curvilinear longitudinal performance development, but nonlinear maturation status interactions were most influential, moderating relationships. In agility sprint, similar trends were apparent, with training time influences diminishing when maturity status was added in LMM analyses. Across time points of maturational growth, increased training engagement was not associated with enhanced physical performance benefits, whereas maturational status progression better accounted for performance differences and development. For coaches and sports-science practitioners, findings question the rationale for heightened training engagement at circa-PHV directed towards physical performance development purposes, a recommendation aligned with the need for maturational-growth associated injury prevention. Instead, due to musculoskeletal and proprioceptive disturbance during maturational growth, training emphasis on technical/biomechanical skill acquisition remains important. Summary Coaches and sports-science practitioners need to recognise that a significant proportion of physical performance development could be attributed to inter-individual maturity-related processes rather than training hours in standard volleyball field test performance. Coaches and sport-science practitioners should understand that, during maturation and the associated heightened growth period (PHV), comparable rates of physical performance improvement may be achieved with reduced training hours. As a result, findings question practitioner decision-making and rationale for increasing training time for physical performance development purposes at circa-PHV. Early sporting engagement intensification (i.e., associated with higher training hours in a single sport context) focused on physiological capabilities (not skill acquisition per se) during maturation may be less valuable for longitudinal progression.
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