## 3 Results and Discussion
### Forefoot Bending Stiffness  
Bending stiffness is the resistive force during metatarsophalangeal (MTP) joint flexion, and the unit of measurement can be Nm/degree, Nm/rad, or N/mm [22]. Forefoot bending stiffness (FBS) refers to the resistance of the forefoot region to flexion around a mediolateral axis, incorporating both upper and midsole structural properties. In badminton, this characteristic plays a crucial role in controlling metatarsophalangeal (MTP) joint motion and distributing ground reaction forces (GRFs) during rapid directional changes. However, existing studies present inconsistent findings regarding its influence on performance and injury risk.  
[PERSON] et al. [10] reported that increased FBS significantly reduced foot torsional range and knee adduction during forward lunges, suggesting a potential protective effect against excessive medial knee loading. However, in high clears, stiffer shoes led to increased knee adduction, indicating possible compensatory movement strategies. In contrast, [PERSON] et al. [14] tested a shoe with a full-length midsole that was 2 mm thinner while maintaining the same back-to-forefoot offset and found no significant differences in agility time, peak shoe torsion, bending angles, or total ankle joint motion during forward lunges.  
These inconsistencies highlight the complex interactions between forefoot stiffness, midsole properties, and movement execution. While increased stiffness has been associated with reduced energy loss at the MTP joint [23], excessive stiffness may limit elastic energy storage and return, particularly in dynamic sports such as badminton [24]. Furthermore, the inclusion of high clears by [PERSON] et al. [10], a movement that engages MTP dorsiflexion more actively, may explain the observed torsional and knee adduction changes. In contrast, the non-significant findings by [PERSON] et al. [14] may be attributed to differences in study design, including midsole thickness, participant sample size, and the specific movement tasks assessed.  
Beyond footwear characteristics, individual athlete variability plays a crucial role in movement biomechanics [25]. Differences in muscle strength, joint flexibility, skillexecution, and movement strategies may significantly impact the effectiveness of footwear modifications. In high clears, for example, variations in hitting point height, swing speed, and directional control can alter lower-limb loading patterns, influencing how forefoot stiffness interacts with player mechanics [26]. Additionally, laboratory-based studies may not fully replicate real-game conditions, where fatigue, court surface compliance, and opponent positioning introduce additional biomechanical constraints.  
The role of gender-specific biomechanics must also be considered. Women's broader forefoot width, higher prevalence of hallux valgus, and distinct plantar pressure distribution suggest a potentially greater sensitivity to forefoot stiffness variations [15]. Additionally, greater knee valgus angles in female athletes may modulate FBS effects on lower-limb loading patterns, underscoring the need for gender-stratified research to refine footwear recommendations.  
While current studies provide valuable insights, further investigations are needed to clarify the interplay between FBS, midsole rigidity, and other shoe parameters under game-replicating conditions. Advances in wearable motion capture systems, force-sensitive insoles, and AI-driven biomechanical modeling will enhance the ecological validity of future research. Moreover, incorporating longitudinal studies with elite and sub-elite athletes will offer deeper insights into the adaptive effects of FBS variations on movement efficiency and injury prevention.