## 3 Results and Discussion
### Shoe Sole Effect  
The shoe sole plays a crucial role in modulating foot-ground interactions, influencing force transmission, shock absorption, and movement efficiency [19; 38]. In badminton, where rapid directional changes and high-impact lunges are frequent, the structural properties of the sole affect both performance and injury risk. Modifications such as midsole stiffness, tread patterns, and wedge structures alter the distribution of ground reaction forces (GRFs) and influence foot stability [23]. A well-designed sole can enhance propulsion efficiency and stability by optimizing force redirection during braking and push-off phases, while excessive rigidity may constrain foot motion, increasing stress on the lower limbs [39].  
[PERSON] et al. [19] examined the effects of a lateral forefoot wedge sole on badminton lunge biomechanics, comparing standard badminton shoes with those featuring an integrated 5\({}^{\circ}\) forefoot wedge. The study assessed lower-limb kinematics and kinetics during lunge movements, measuring how sole modifications affect GRF, stance time, and force application mechanics. The findings demonstrated that forefoot wedge soles significantly improved mechanical performance. Specifically, the horizontal ground reaction force (GRFh) increased by 7.8% in forward lunges, while the H/V ratio increased by 6.4% in backward lunges, indicating that the wedge facilitates more efficient force redirection [19; 40]. These improvements can be attributed to the wedge's ability to redistribute plantar pressure toward the lateral forefoot, enhancing push-off efficiency--aligning with previous research on footwear stiffness and pressure distribution [14; 39]  
The subjective preference for wedge shoes in stability and comfort further supports the idea that proprioceptive feedback plays a critical role in footwear design. Enhanced ankle stability may stem from increased lateral support, reducing excessive inversion moments and potentially lowering the risk of lateral ankle grains [41]. The 5\({}^{\circ}\) wedge incline in this experiment alters foot contact dynamics, mimicking the mechanical advantage seen in inclined sprint start positions, which amplify horizontal force output by modifying foot placement angles [42]. However, whether these biomechanical principles directly translate to lateral movements in badminton remains to be further validated.  
While this study provides valuable insights, several limitations must be acknowledged. The added mass from the external wedge prototype may have influenced GRF measurements, necessitating further research using integrated wedge designs to minimize weight discrepancies [19]. Additionally, testing only a single wedge angle (5\({}^{\circ}\)) limits generalizability, as previous research on lateral shuffle movements suggests that a 10\({}^{\circ}\) incline may better balance performance gains with joint loading concerns [39]. The exclusion of female and elite athletes further limits the applicability of these findings to broader badminton populations.  
The lateral forefoot wedge sole presents a promising innovation for optimizing badminton lunge biomechanics, particularly in multidirectional force generation and footwork stability. However, long-term safety considerations, adaptive responses, and commercial footwear integration require further study to ensure performance benefits do not come at the expense of increased musculoskeletal stress.