## 4 Discussions
### Velocity Effects  
Regarding the increased velocity effects, hip ROM and ankle ROM increased to varying extents [37], while the bionic shoes and neutral shoes also yielded different results. In our study, from 10 km/h to 14 km/h, knee ROM while wearing the bionic shoes showed a greater decrease than for the neutral shoes. Previous studies have implied that in bionic shoes, a reduction in joint ROM served to strengthen muscle control, which may increase the activation of relative muscle groups and reduce the risk of falling [38]. Other studies [39; 40] have also found that the unstable element of the midsole could strengthen muscle control. In our study, the peak angular velocity of the knee joint showed a significant increase, which indicated a shorter time to complete the running gait. As explained by previous studies, at higher gait velocities, a greater amount of power is required to propel the body forward, leading to this outcome [41]. Another finding is that ankle ROM and knee ROM in the bionic shoes showed greater decreases, while ankle ROM increased, and knee ROM showed a smaller decrease in the neutral shoes. Hence, we observed a magnitude decrease in the proportional contribution of ankle ROM in the bionic shoes compared with the neutral shoes when the velocity increased. Previous studies have also associated sprinting ability with specific ankle plantar-flexor properties [42]. These characteristics contributed to enhanced force generation and power output in the bionic shoes during the propulsion phase of sprinting, allowing for greater velocity and acceleration. Simultaneously, the neuromuscular system, sensorimotor system, and proprioception were enhanced passively to adjust the ROM of the low limbs, especially for ankle ROM, to an inherently safer range to avoid injury [43]. From V2 to V3, hip ROM in the neutral shoes showed a magnitude increase, while no significant differences were found in this regard in the bionic shoes. This finding may indicate that from jogging running to training running, the bionic shoes brought a more stable condition for the hip joint for runners to achieve their training effect. With increasing running velocity, the peak ankle moment increased more than the peak knee moment. Recent indications suggest that as running velocity increases, there is a greater burden placed on the plantar flexors of the ankle joint compared to the extensors of the knee joint [44]. This finding suggests that when running at an excessive pace, the structures located in the posterior part of the lower leg and underneath the foot are potentially more vulnerable to injury compared to the structures in the anterior part of the knee [16]. In general, the maximum power and the positive work and negative work of the hip and ankle joints were affected by increases in running velocity. In particular, the maximum power of the hip and ankle, hip positive work, and ankle work (both positive and negative) were all significantly affected by running velocity under all the conditions tested. When running velocity increased, the positive work performed by the hip and ankle showed a significant increase, while no significant changes were observed in the knee joint. Previous studies have also found that accelerated velocity appears to be particularly dependent on the performance of the hip and ankle joints [45]. Furthermore, for the ankle joint in the bionic shoes, positive work, negative work, and maximum power showed larger values than in the neutral shoes at slower velocities but showed little differences compared with the neutral shoes at faster velocities. This may indicate that the bionic shoes were good at absorbing power and that they are more suitable for running at a training velocity or a faster velocity since the ankle plantar-flexor muscles play a significant role in generating the primary contribution among the major muscles of the lower limbs to vertical and forward acceleration during the stance phase of sprinting [46; 47].