To investigate autonomic adaptation to subalpine environment and exercise load. Methods: Thirteen middle-distance runners were studied and trained for 6 weeks in a subalpine plateau at an altitude of 1,770 m. TRIMP was applied to monitor the exercise load and to detect HRV indexes during the training period. Results: ① Compared with week 1, TRIMP values increased significantly at week 4 and week 6 in the subalpine (P<0.01); ② Compared with baseline data, HRV indexes showed a significant decrease in SDNN and RMSSD at week 1 in the subalpine (P<0.05); and LF and LF/HF increased significantly at week 1 (P<0.05); compared with week 1: RMSSD increased significantly in week 3 (P<0.01), LF decreased significantly in week 3 (P<0.01), LF/HF decreased significantly in weeks 3 and 6 (P<0.05); compared to week 3: RMSSD, HF decreased significantly in week 4, (P<0.05); LF/HF increased significantly in week 4 (P<0.05); compared to week 4: HF significantly increased at week 6 (P<0.01), LF/HF significantly decreased at week 6 (P<0.01), and SD2 changes during the 6-week subaltern training period are not statistically significant. Conclusion: In the initial phase of sub-plateau training, athletes experience an increase in sympathetic nervous system activity, leading to autonomic nervous system imbalance; however, this improves after two weeks. During the mid-phase, increasing exercise load and implementing adaptive recovery significantly enhances vagus nerve activity, which helps better cope with exercise demands. |