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.