## 4 Discussion
### Effects of Subalpine Training on the Athletic Performance of Cross-Country Skiers  
#### 4.2.1 The Effect of Subalpine Training on Athletes' Specific Sport Performance Abilities  
The V2 technique is very important for cross-country skiing in freestyle and is also a technique that is used more often in cross-country skiing competitions [44]. To better control the speed, slope, and test time of the athletes, the V2 technique was chosen to test the athletes' ability to glide at nine levels before and after the subalpine, with the average heart rate, immediate blood lactate, and RPE for each level completed. The accumulation of blood lactate is a product of anaerobic metabolism during exercise and its accumulation can cause a certain degree of decline in muscle performance [45; 46]. The elimination of lactate is mainly through oxidative metabolic pathways and the rate of elimination is somewhat reflective of the athlete/s aerobic metabolic capacity [47]. After subalpine training, the blood lactate concentration of both male and female athletes showed a significant decrease under the same intensity of special training on treadmill roller-skiing, indicating that the athletes' ability to disperse blood lactate and lactate tolerance had greatly improved [48].  
After long-term subalpine training, for the same special roller-skiing intensity, the average heart rate of both male and female athletes showed a significant difference, the male athletes' heart rate increased at the 2 nd-5 th level, and then the heart rate slowly stabilized, indicating that the athletes had a lower heart rate response than before in special training, and can grasp the rhythm of special training at different intensities. This helps athletes not to be disturbed after overtaking their opponents in a competition and to be able to distribute their energy rationally and optimize their performance. After subalpine training, female athletes showed a significant decrease in average heart rate between levels 1-6, indicating that female athletes have improved their ability for this level and the athletes had a lower heart rate response than before subalpine training.  
There was no significant difference in RPE values between male and female athletes after subalpine training, however, we can see from Figure 5 that the change in RPE values was the same as the change in blood lactate, indicating that the athletes had a more accurate assessment of themselves, which would be of great help in controlling their training load in the following training.  
.2.2 The Influence of Sub-Altitude Training on Athletes' Performance in Strength and Speed Endurance  
After subalpine training, in terms of strength, the absolute value of 1 RM' squat of both male and female cross-country skiers showed a significant increase, indicating that during subalpine training, the lower limb strength of athletes improved significantly; the 1 RM' bench press of male athletes increased significantly, while that of female athletes increased only slightly and was not statistically significant, indicating that subalpine training improved the upper limb strength of male athletes much more than that of female athletes. It is much higher than that of female athletes. The change was significantly higher in male athletes than in female athletes, an idea also argued by [PERSON] et al., who found the male athletes demonstrated 87%, 97%, and 103% higher power output than the female during whole-body (WP), upper-body (UP), and arm poling (AP) respectively [49].  
For the 30 m fast sprint, after subalpine training, there was no significant change for male or female athletes, indicating there was no impact on speed or explosive power; however, there was a significant increase in the 10 km endurance run for male and female athletes, indicating that the endurance training of athletes was greatly improved after subalpine training. This view is also evident from the significant decrease in blood lactate concentration immediately after special training.