The influence of age and maturation on trajectories of stretch shortening cycle capability in male youth team sports

Purpose: To examine the the influence of growth and maturation in the trajectory of stretch shortening cycle (SSC) capability. Method: Using a mixed longitudinal design absolute and relative leg stiffness, and reactive strength index (RSI) were measured three times over a three-year period in 44 youth team sport players. Maturation was determined as maturity-offset and included within the Bayesian inference analysis as a covariate alongside chronological age. Results: Irrespective of age and maturation there was no change in absolute leg stiffness, however relative leg stiffness decreased over time. Maturation and age reduced this decline, but the decline remained significant (BF10 = 5097, model averaged R2 = 0.61). RSI increased over time and more so in older more mature youth players (BF10 = 9.29e8, model averaged R2 = 0.657).. Conclusion: In youth players who are at/post peak height velocity, relative leg stiffness appears to decline, which could have an impact on both performance and injury risk. However, RSI increases during this period, and these data reinforce that leg stiffness and RSI reflect different components of SSC capability. Practitioners should consider these differences when planning training to maximise SSC capability during growth and maturation in athletes on the developmental performance pathway.