## 4 Discussion
### Predictive Validity  
The current study found that the step frequency during both the acceleration phase and the steady-state phase, along with the glide length obtained during the steady-state phase, were the most important kinematic metrics in predicting the maximal skating velocity. Since there have been no regression models conducted yet to predict the maximum skating velocity from spatiotemporal parameters obtained using skate-mounted IMUs, it is only possible to compare our results with those of studies that aimed to identify biomechanical characteristics that differentiate between high- and low-caliber hockey players, leading to a faster skating performance [5; 14; 15; 48; 49].  
Specifically, [PERSON] et al. [5] showed that faster skaters had similar step lengths, but shorter skate contact and double support times, with a higher stride frequency during the skate start. Likewise, [PERSON] et al. [14] reported a higher skating velocity, stride propulsions, and lower contact time (i.e., higher step frequency) in high-caliber than low-caliber players. Given that power is the product of stride frequency and the amount of force applied on the ice by each stride, logically, a faster forward propulsion and speed could be attained by maximizing the frequency and distance over which the force is exerted [32]. The optimal way to do it is to move the lower-body limbs as far as possible through the range of motion, while keeping a high stride frequency [15; 32; 49; 50; 51]. Previous studies have demonstrated that this can be achieved through high activation of the hip flexors and relaxation of the antagonist muscles (e.g., the gluteus maximums), along with fast and large hip abduction, which together results in a rapid swing phase (i.e., a higher step frequency) and a longer glide [15; 48; 50; 51].  
In addition, our study corroborates with the findings by [PERSON] et al. [49] regarding the importance of stride frequency in forward skating during the steady-state phase. According to their research, faster skaters could be differentiated from slower skaters based on their stride frequency during the steady-state phase. However, the comparison between our results and theirs may be debatable since they carried out their research on a skating treadmill. Moreover, glide length obtained only during the steady-state phase significantly determined the maximal velocity. This can be attributed to faster skaters having better reactive strength, a larger ankle plantar flexion and knee extension at push-off, and a larger hip range of motion (i.e., increased hip flexion and abduction) and concentric force development during the glide phase [5; 15; 48; 49; 52].  
Consequently, this could provide them with increased glide length and, thus, a longer distance at which the force is applied. If this is accompanied by a high step frequency, and a faster forward propulsion, ultimately an increase in speed can be expected. Furthermore, it is worth noting that [PERSON] et al. [14] showed a stronger correlation between stride propulsion velocity and the total sprint time registered during the acceleration phase than that obtained during the steady-state phase, which demonstrates the importance of the acceleration phase in achieving the maximal skating velocity. This is in line with our findings, which showed that while step frequency determines the maximal velocity, a greater contribution was made by the step frequency obtained during the acceleration phase rather than the steady-state phase.