Foot orthoses alter lower limb biomechanics but not jump performance in basketball players with and without flat feet

Background: Flat-footed individuals are believed to have poorer jump performance compared to normal-arched individuals. Foot orthoses are commonly used to support the deformed foot arch, and improve normal foot function. However, it is unclear if foot orthoses use affects jump performance in athletes. Our study aims to investigate if foot type and/or foot orthosis influence countermovement jump (CMJ) and standing broad jump (SBJ) performance and lower limb biomechanics. Methods: Twenty-six male basketball players were classified into normal-arched (n = 15) or flat-footed (n = 11) groups using the Chippaux-Smirak index, navicular drop test, and the resting calcaneal angle measurement. They performed jumps with and without prefabricated foot orthoses. We measured jump height and distance for CMJ and SBJ, respectively. Hip, knee and ankle joint angles, angular velocities, moments and powers during take-off were also measured. Results: For CMJ, the flat-footed group exhibited less ankle plantarflexion (F1,24 = 8.407, p = 0.008, ηp 2 = 0.259 large effect) and less hip joint power (F1,24 = 7.416, p = 0.012, ηp 2 = 0.244 large effect) than the normal-arched group. Foot orthoses reduced ankle eversion in both groups (F1,24 = 6.702, p = 0.016, ηp 2 = 0.218 large effect). For SBJ, the flatfooted group produced lower peak hip angular velocity (F1,24 = 7.115, p = 0.013, ηp 2 = 0.229 large effect) and generated lower horizontal GRF (F1,24 = 5.594, p = 0.026, ηp 2 = 0.189 large effect) than the normal-arched group. Wearing foot orthoses reduced ankle eversion (F1,24= 5.453, p = 0.028, ηp2 = 0.185 large effect), peak horizontal GRF (F1,24 = 13.672, p = 0.001, ηp2 = 0.363 large effect) and frontal plane ankle moment (F1,24 = 4.932, p = 0.036, ηp2 = 0.170 large effect). Conclusion: Foot type and the use of foot orthoses influence take-off biomechanics, but not actual CMJ and SBJ performances in basketball players. Compared to the normal-arched individuals, flat-footed athletes generated smaller propulsion GRF and lower hip flexion velocity and power, which suggests possible compensatory movement strategies to maximise jump performance. Future studies may investigate whether these altered biomechanics, taking into consideration their respective magnitude and effect sizes, may have implications on lower limb injuries. The use of foot orthoses resulted in biomechanical changes in both the normal-arched and flat-footed groups but does not enhance jumping performance.