## 3 Results and Discussion
### Midsole Hardness Effect  
Midsole hardness plays a critical role in impact attenuation, energy return, and force transmission, especially in sports involving frequent jumping and landing [43]. The midsole serves as a cushioning and supportive layer between the insole and the outside, influencing how forces are absorbed and redistributed across the lower limbs [21]. Footwear design in badminton must balance propulsion efficiency during takeoff and impact mitigation upon landing, as excessive stiffness may compromise shock absorption, while excessive softness may reduce energy transfer efficiency [44]  
[PERSON] et al. [21] investigated the effects of midsole hardness, comparing 62C (soft) and 68C (hard) midsoles using temporal-spatial and ground reaction force (GRF) analyses during badminton scissor jumps. Their study found no significant differences in jump height or GRF variables during takeoff, indicating that midsole hardness does not substantially affect propulsion performance. However, during landing, the harder midsole condition resulted in a significantly higher vertical impact peak (\(p\) = 0.008), suggesting that shock attenuation may be reduced with increasing stiffness. The study also reported a longer time-to-vertical impact peak (\(p\) = 0.007) and a lower loading rate (\(p\) = 0.013) in the harder midsole condition, which may indicate a different force dissipation strategy rather than a straightforward cushioning deficit.  
These findings align with previous research on midsole hardness in various sports. [PERSON] et al. [45] demonstrated that softer midsoles in basketball footwear improved impact attenuation, reducing peak GRF and loading rates during unanticipated landings. Similarly, [PERSON] [44] emphasized that cushioning properties are essential for minimizing impact forces, particularly in sports with repeated jump landings. However, a study by [PERSON] et al. [21] highlights that while harder midsoles do not necessarily enhance propulsion, they do alter shock absorption mechanics, as evidenced by higher impact peaks and prolonged force application times.  
A longer time to vertical impact peak is often associated with improved impact attenuation, yet the interaction between midsole hardness and force dissipation remains complex. A harder midsole may delay force dissipation, which could alter lower-limb loading strategies and increase localized stress on the heel and forefoot. This is particularly relevant for male athletes, who exhibit a significantly higher incidence of heel pain compared with female athletes [15]. A stiffer midsole could exacerbate such injuries by increasing localized plantar pressures, necessitating the adoption of gradient midsole hardness designs, such as a softer heel for impact absorption and a firmer forefoot for energy return.  
Further research should explore how emerging cushioning technologies, such as rotational shear-cushioning structures, can optimize both performance and safety in badminton footwear. Additionally, understanding how midsole properties interact with athlete-specific factors, such as body weight, foot arch structure, and playing style, will be essential for developing customized footwear solutions that enhance both jumping performance and impact protection.