This study examined the effects of a short-duration supplementary strength–power training program on neuromuscular performance and sport-specific skills in adolescent athletes. Twenty-three female “Gymnastics for All” athletes, aged 13 ± 2 years, were divided into a training group (TG, n = 12) and a control group (CG, n = 11). Both groups underwent a test battery before and after 10 weeks of intervention. TG completed, in addition to gymnastics training, a supplementary 7–9 min program that included two rounds of strength and power exercises for arms, torso, and legs, executed in a circuit fashion with 1 min rest between rounds, three times per week. Initially, six exercises were performed (15 s work–15 s rest), while the number of exercises was decreased to four and the duration of each exercise was increased to 30 s (30 s rest) after the fifth week. TG improved countermovement jump performance with one leg (11.5% ± 10.4%, p = 0.002) and two legs (8.2% ± 8.8%, p = 0.004), drop jump performance (14.4% ± 12.6%, p = 0.038), single-leg jumping agility (13.6% ± 5.2%, p = 0.001), and sport-specific performance (8.8% ± 7.4%, p = 0.004), but not 10 m sprint performance (2.4% ± 6.6%, p = 0.709). No change was observed in the CG (p = 0.41 to 0.97). The results of this study indicated that this supplementary strength–power program performed for 7–9 min improves neuromuscular and sport-specific performance after 10 weeks of training.