Long-Term Effects of NASM-OPT Periodized Training on Lower-Limb Strength, Explosive Power, and Stretch-Shortening Cycle Function in Adolescent Athletes

Strength training plays an essential role in improving performance and lowering injury incidence among adolescent athletes. However, current training practices often involve premature specialization, insufficient load management, and adult-oriented programming. The periodized National Academy of Sports Medicine's Optimum Performance Training (NASM-OPT) model develops stability, strength, and lower-limb power in a progressive manner, but its long-term effects in adolescents remain unclear. This randomized controlled trial compared NASM-OPT with traditional periodized training to examine the effects on maximal lower-limb strength and explosive power among 42 adolescent athletes randomly allocated to the OPT and CON groups (n = 21 per group). A 26-week intervention was completed in both groups. Squat one-repetition maximum (1RM), countermovement jump (CMJ), squat jump (SJ), pre-stretch augmentation percentage (PSAP), and eccentric utilization ratio (EUR) were assessed at baseline and post-intervention. Repeated-measures ANOVA was used to analyze group×time interactions (α = 0.05). Compared with the CON group, the OPT group demonstrated greater post-intervention values in 1RM (133.1 ± 21.4 vs 119.2 ± 18.0 kg), CMJ (47.4 ± 5.8 vs 39.8 ± 4.0 cm), PSAP (10.63% vs 6.07%), and EUR (1.11 vs 1.06) post-intervention (p < 0.05). The OPT group maintained these improvements throughout the intervention, whereas the CON group showed plateaued values, potentially suggesting enhanced stretch-shortening cycle(SSC) function. Periodized NASM-OPT training efficiently promotes lower-limb strength, explosive power, and SSC function in adolescent athletes. These findings indicate that systematic and progressive programming can optimize performance while minimizing injury risk.