Understanding the Biomechanical Profiles of MTP Joint in Badminton Players during Split-Step of Directional Lunges

This study aimed to investigate the biomechanical influence of the split-step (SS) on the metatarsophalangeal (MTP) joint during the initiation of multi-directional lunges in badminton. Fourteen right-foot-dominant male badminton athletes performed lunges at 0°, 45°, 90°, and 135° under SS and no split-step (nSS) conditions. The kinematics of the knee, ankle, and MTP joints and ground reaction force data were collected using a Vicon 3D motion capture system and a force platform. Joint angles and joint moments were calculated as intermediate biomechanical variables to derive joint range of motion (ROM) and MTP quasi-static stiffness(ΔM/Δθ; hereafter referred to as stiffness). Joint ROM and MTP joint stiffness were analyzed using repeated-measures ANOVA across movement directions and conditions. A significant direction×condition interaction was found for MTP stiffness (p < 0.05), with SS showing directionally modulated stiffness values, although post-hoc comparisons did not reach statistical significance. SS significantly reduced sagittal-plane MTP ROM at 0° and increased it at 135° (p < 0.05). In contrast, the nSS condition demonstrated greater MTP ROM and variability, particularly in frontal and transverse planes. Several joint angles showed the direction versus condition interactions, suggesting that the effect of SS varies across lunge directions. The SS enhances distal joint control by increasing MTP joint stiffness and reducing excessive ROM, promoting more efficient propulsion and multiplanar joint stability during directional movements.