<p>This study aimed to compare the effects of complex training (CT) and resistance training (RT) on lower-limb strength and power performance in adolescent long jumpers. It was hypothesized that complex training would result in more significant improvements in performance compared to traditional resistance training. A total of 36 male adolescent long jumpers (mean age 15 years) participated in an 8-week randomized controlled trial. Participants were randomly assigned to either a complex training group (<i>n</i> = 18) or a resistance training group (<i>n</i> = 18). Strength and performance were measured before and after the intervention, including tests for one-repetition maximum (1RM) squat, isometric mid-thigh pull (IMTP), vertical jump (VJ), standing long jump (SLJ), pre-stretch augmentation percentage (PSAP), and reactive strength index (RSI). Significant group × time interactions were observed for 1RM squat (<i>p</i> = 0.002, Partial η² = 0.965), IMTP (<i>p</i> &lt; 0.001, Partial η² = 0.909), VJ (<i>p</i> &lt; 0.001, Partial η² = 0.798), SLJ (<i>p</i> &lt; 0.001, Partial η² = 0.894), and RSI (<i>p</i> = 0.001, Partial η² = 0.667). PSAP showed no significant interaction (<i>p</i> = 0.156), but a main effect of time was detected (<i>p</i> = 0.030). Complex training is a more effective strategy than resistance training for improving lower-limb strength and power in adolescent long jumpers. The combination of resistance and plyometric exercises in complex training leads to better performance outcomes, making it an optimal training method for long jumpers.</p>