## 4 Discussion
### Knee Joint Kinetic Performance: Eccentric Power, Concentric Power, and Extension Moment  
The present study revealed that both fast- and moderate-velocity flywheel resistance training significantly improved knee joint kinetic performance, as reflected in increases in the eccentric power (EP), CP, and EM. These improvements were predominantly observed within 4 to 12 min post-exercise, exhibiting a typical PAP profile. In contrast, slow-velocity training failed to produce similar effects, indicating suboptimal neuromuscular activation under such loading conditions.  
Moderate-velocity training elicited the greatest gains in EP. This result may be attributed to longer eccentric phase duration and more stable force production at moderate velocities, creating a favorable time-under-tension stimulus that enhances mechanical loading and structural adaptation. [PERSON] et al. emphasized the importance of eccentric tempo in maximizing neuromuscular efficiency [35]. Similarly, [PERSON] et al. highlighted that high mechanical loading during eccentric exercise activates muscle spindles and high-threshold motor units, facilitating enhanced force development [36]. In addition, [PERSON] et al. found that inertial training improved performance outcomes without additional motor unit recruitment, suggesting neuromechanical efficiency during eccentric-concentric transitions [37].  
CP increased significantly under both fast and moderate conditions, albeit through different mechanisms. High-velocity training emphasizes the rapid neural drive and preferential activation of type II fast-twitch muscle fibers, contributing to increased rate of force development. Conversely, moderate-speed training offers extended contraction durations, which may promote better force summation and efficiency of energy transfer. [PERSON] et al. identified similar patterns, noting that contraction duration is a critical factor in maximizing concentric output [38]. [PERSON] et al. found that flywheel resistance training produced greater improvements in power-related performance--such as the jump height and sprint speed--compared to volume-matched traditional strength training, despite similar gains in maximal strength [39].  
Regarding EM, improvements were more pronounced under moderate-velocity training. This finding suggests that moderate loads may be more effective in enhancing maximal strength development and joint torque capacity. [PERSON] et al. linked increased extension moment to enhanced quadriceps output and better joint stabilization [40]. Likewise, [PERSON] et al. found that eccentric training improves stress distribution and extension control at the knee joint, particularly when combined with appropriate structural loading [41].  
Physiologically, these adaptations are likely the result of both central and peripheral mechanisms. Centrally, flywheel training enhances the excitability of alpha motor neurons and promotes more synchronized motor unit recruitment, as demonstrated by [PERSON] et al. [42]. Peripherally, an increased sarcoplasmic calcium ion concentration and greater myosin light chain phosphorylation, as described by [PERSON] and [PERSON], improve excitation-contraction coupling and cross-bridge kinetics [43]. Moreover, chronic adaptations such as enhanced tendon stiffness and more efficient energy transfer, reported by [PERSON] et al., contribute to the observed improvements in force production quality [44].  
Moreover, accumulating evidence has emphasized the velocity-dependent nature of neuromuscular adaptations. [PERSON] et al. observed that high-velocity flywheel protocols are more effective in enhancing short-term peak power output, whereas moderate-velocity loading is more beneficial for improving sustained force output and neuromuscular tension regulation [25]. These findings are consistent with the present results and further reinforce the importance of tailoring velocity-specific loading strategies to match performance goals in training interventions.