To investigate the differences in physical fitness and physiological indexes of male soldiers stationed at different altitudes and to analyze the determinants of physical fitness of these soldiers.

A total of 13648 male soldiers at different altitudes were included, whose results of annual military physical assessment and physiological indexes in 2023 were collected and comparatively analyzed.

The 3000-meter running performance,30-meter × 2 serpentine running performance and resting blood oxygen saturation of high-altitude soldiers gradually declined with the increase of altitudes. The pull-up performance dropped significantly when the altitude > 2000 m. Soldiers ≥30 years old demonstrated a marked decline in physical fitness across different training programs. Moderate altitude acclimatization was conduciveto the recovery of physical fitness of soldiers, while exposure to high-altitude environment ≥5 years led to overall deterioration.

The high-altitude environment significantly impacts the aerobic endurance, speed, agility, and strength of soldiers. Altitude ≥4000 m, age ≥30 years, and prolonged exposure ≥5 years may contribute to the decline in physical fitness of soldiers.

To explore the changes in biochemical indicators among soldiers with different endurance qualities after high altitude exposure and their adaptation to plateau environment.

A status survey was carried out on 253 young male soldiers who were planned to station in Malone, Yunnan Province（2 100 m）for 4 weeks from July to August, 2018. The sampling method is cluster sampling. The endurance quality and biochemical indicators were assessed and measured before exposure and after 4 weeks' training. Their endurance quality was evaluated with grading 3-km armed cross-country. The included biochemical indicators were levels of creatine kinase, hemoglobin, average hemoglobin and cardiac troponin, and counts of blood red cells, lymphocytes and basophils.

Based on the results of the 3-km armed cross-country, the participants were divided into excellent（12%）, good（21%）, passing（40%）and failing（27%）groups. Except for basophil counts, levels of creatine kinase, cardiac troponin, hemoglobin and average hemoglobin, and counts of red blood cells and lymphocyte changed significantly in all the 4 groups before and after high altitude exposure（P<0.01）. While, obvious changes were observed in cardiac troponin level and lymphocyte count among the 4 groups after they were stationed at high altitude（P<0.01）, and these changes were correlated with endurance quality（cardiac troponin: r_s=-0.409, P<0.01; lymphocytes: r_s=0.205, P<0.01）.

There are some differences in blood biochemical indicators in soldiers with different endurance qualities at high altitude. Our results suggest that soldiers with higher endurance quality have a relatively lower risk of myocardial injury and stronger immune function after entering high altitude.