Ulviye Uğur ÖZYILMAZ, Erkan ÖZYILMAZ, Tuğçe Duman ÖZKAN, Seyit ÇİTAKER, Abdullah Yener İNCE
The Injector - 2026;5(2):73-85
Objective: This pilot study aimed to compare the acute effects of Accentuated Eccentric Loading (AEL) jump squat exercise performed with modified and neutral foot positions on muscle stiffness and performance outcomes in adolescent footballers. Methods: Ten male footballers aged 13-17 years, training at least three days per week, were included in the study. Participants performed an AEL jump squat protocol of 3x10 repetitions with free weights corresponding to 30% of body weight in both foot positions, one day apart. Muscle stiffness was measured using MyotonPRO(R) in the vastus lateralis (VL), gastrocnemius medialis/lateralis (GM/GL), and biceps femoris (BF) muscles; performance was assessed before and after exercise using the vertical jump, single-leg forward jump, Y Balance Test (YBT), and T-Test. Results: In muscle stiffness measurements, a significant decrease was observed only in the VL after neutral AEL (Delta=-48.4 +/- 64.15 N/m; p=0.037), while no significant change was observed after modified AEL (p=0.906). Vertical jump-related variables increased following both conditions; however, the increase in maximum concentric phase velocity (CPV) following modified AEL was not statistically significant (p=0.050). Neutral AEL led to a significant increase in the modified reactive strength index (RSI-mod) (Delta=+0.04+/-0.07; p=0.037) and a marked decrease in landing force (Delta=-1178.7+/-643.48 N; p=0.005). T-Test completion time increased significantly only after neutral AEL (Delta=+0.28+/-0.27 s; p=0.013), indicating impaired agility performance. In the YBT, right-leg posterolateral reach distance increased significantly after modified AEL (Delta=+5.43+/-6.57 cm; p=0.012). For the left leg, significant increases were observed in the posteromedial direction after modified AEL (p=0.028) and in the posterolateral direction after neutral AEL (p=0.037). No significant between-condition differences were detected for the changes in the assessed outcomes. Conclusion: AEL jump squat exercise produced outcome-specific acute responses in adolescent footballers. Neutral AEL was associated with decreased VL stiffness, increased RSI-mod, reduced landing force, and increased T-Test completion time, whereas modified AEL was associated with improvements in selected YBT reach directions. However, because no significant between-condition differences were detected, the findings do not demonstrate the superiority of either foot position. Rather, the results suggest that AEL may elicit task-specific acute responses, which should be confirmed in adequately powered studies.
