Background Basketball requires a solid foundation of lower limb strength and explosive power. Unilateral and bilateral resistance training modes may differ in improving sport-specific performance, but their relative effects and potential advantages in trained adolescent athletes remain unclear. This pilot study aims to explore the application effects of these two methods on specific performance indicators. Objective This exploratory study aimed to compare the effects of a seven-week unilateral eccentric training (UET) and bilateral eccentric training (BET) on lower limb maximal strength, jump, and sprint performance in trained adolescent male basketball players. Methods Twelve participants (n=12) were randomly assigned to either a UET or BET group. In addition to completing six hours of regular basketball training per week, both groups performed unilateral or bilateral eccentric resistance training three times a week for seven weeks. Three categories of performance indicators were comprehensively assessed pre- and post-intervention: 1) lower limb maximal strength (estimated values: Advantage Unilateral Bulgarian Squat [AUBS], Advantage Unilateral Deadlift [AUD], Bilateral Squat [BS], and Bilateral Deadlift [BD]); 2) jump performance (Standing Triple Jump [STJ], Standing Advantage Unilateral Reach Height [SAURH], and Standing Bilateral Reach Height [SBRH]); and 3) sprint performance (30-meter sprint). A Bayesian mixed-effects model was used for an exploratory analysis of the posterior probabilities of performance changes. Results One. Between-group analyses revealed that neither the UET nor the BET group demonstrated a statistically significant between-group advantage across all tested indicators (posterior probabilities < 97.5%). 2. Regarding lower limb maximal strength, within-group exploratory analyses indicated that only the UET group showed a high probability of improvement in the estimated AUD (98.25% probability, g = 12.01,95% CrI [1.04 - 22.87]). The other strength indicators (AUBS, BS, BD) did not exhibit clear high-probability improvement trends in either group. 3. Regarding jump performance, the UET group demonstrated extremely high improvement potential in SAURH (99.74% probability, g = 9.12, 95% CrI [3.41 - 14.81]) and SBRH (98.43% probability, g = 7.60, 95% CrI [0.96 - 14.29]). Concurrently, the BET group also showed a high probability of improvement in SBRH (97.56% probability, g = 6.76, 95% CrI [0.04 - 13.79]). However, neither group displayed a high-probability adaptive enhancement in the STJ metric. 4. Regarding sprint performance, only the UET group exhibited a high probability of improvement in the 30-meter sprint time (99.03% probability, g = 0.27, 95% CrI [0.05 - 0.48]), whereas the BET group did not present a similar high-probability trend. Conclusion Although both UET and BET interventions demonstrated within-group potential to improve specific sports performance metrics (e.g., partial maximal strength, jump, and sprint capabilities) in trained adolescent basketball players, neither modality established a statistically significant absolute between-group advantage. Future large-scale studies, strictly controlling for training volume and concurrent sport-specific loads, are required to further validate these exploratory findings. Trial registration (Retrospectively registered): Chinese Clinical Trial Registry, Registration number: ChiCTR2500114472, Reg Date: 2025-12-12.
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