Effects of Different Moments of Inertia on Neuromuscular Performance in Elite Female Soccer Players During Hip Extension Exercise to Prevent Hamstring Asymmetries and Injuries: A Cross-Sectional Study

Background/Objectives: High-intesity actions such as accelerations and decelerations are essential for elite female football performance and are often executed unilaterally, increasing the risk of interlimb asymmetries and injuries. Flywheel resistance training has gained popularity for its ability to enhance eccentric strength, but evidence on how specific inertial loads influence mechanical outputs in unilateral exercises remains limited. This study aimed to examine the effects of altering moments of inertia (0.107 kg·m² and 0.133 kg·m²) on the peak and average power, acceleration, speed, and bilateral asymmetry during a hip extension exercise in elite female football players. Methods: A repeated-measures cross-sectional design was used. Eighteen (27 ± 4 years, 59.9 ± 6.5 kg, 168,2 ± 6.3 cm; 21.2 ± 1.8 IMC) professional female football players performed unilateral hip extension on a conical flywheel device under two inertial conditions. A high-resolution rotatory encoder recorded peak and average values for power, acceleration, and speed, as well as the eccentric-to-concentric (E:C) ratio. Bilateral asymmetry was analyzed between dominant limb (DL) and non–dominant limb (NDL). Paired t-tests were applied, and Cohen’s d effect sizes were calculated. Results: Higher inertia (0.133 kg·m²) significantly decreased peak and mean acceleration and speed compared to lower inertia (0.107 kg·m²) (p < 0.001, d > 0.8. No significant differences were found in concentric peak and mean power for either limb, whereas eccentric peak power significantly increase only in the NDL limb (p < 0.001, d = 3.952). E:C ratios remained stable across conditions. Conclusions: Increasing inertial load during unilateral flywheel hip extension decreased significantly peak and mean acceleration and speed, while eccentric peak power only in the NDL. These findings suggest that manipulating inertia can help regulate neuromuscular training and manage performance asymmetries in elite female football players.