Leg stiffness and countermovement jump performance in young male soccer athletes: Insights into maturation effect

Determining leg stiffness and countermovement jump (CMJ) performance as soccer athletes mature may provide valuable insights into the mechanisms of CMJ during the developmental period and may help soccer trainers target specific objectives and design more effective training programs. This study aimed to examine in young male soccer athletes of different maturity levels (a) CMJ performance and leg stiffness, and (b) the relationship between CMJ performance and leg stiffness. Fifty-six young soccer athletes characterized as pre- (n = 25), circa- (n = 17), and post-peak height velocity (PHV) (n = 14), according to their maturity offset, performed three CMJs, and, to evaluate leg stiffness, submaximal hops at a frequency of 2 Hz. Circa-PHV athletes did not differ from post-PHV in CMJ performance and leg stiffness values, but both groups presented higher CMJ height and leg stiffness values than pre-PHV athletes. There was a strong correlation between leg stiffness and CMJ performance only in post-PHV soccer athletes. In conclusion, both vertical jump performance and leg stiffness of young male soccer players increase upon entry into adolescence. Furthermore, the fact that the vertical jump performance of more mature players (post-PHV) is related to greater leg stiffness could be attributed to the maturation process. These findings suggest that adapting training strategies to focus on building leg stiffness for fast movements early in the maturation process, while integrating these benefits into slow SSC tasks like the CMJ later in the post-PHV phase, may optimize physical development and performance outcomes for young soccer athletes.