Objective To analyze the relationship between hypoxic cardiopulmonary endurance and normoxic physiological indicators of firefighters in order to investigate the physiological characteristics of firefighters'adaptation to hypoxia.

Methods From March to June 2024, a total of 42 active-duty firefighters from Dongcheng District, Beijing, were recruited as study subjects. Resting physiological indicators-including blood pressure, heart rate, and blood oxygen saturation-were measured under normoxic and two simulated hypoxic conditions equivalent to altitudes of 1 800 m and 2 800 m. Assessed the maximal oxygen uptake (VO_{2, max, 2 800}) in the hypoxic environment at 2 800 m, investigating the relationship between the VO_{2, max, 2 800} percentage of predicted VO_{2, max}, and physiological indicators at rest under a normoxic environment.

Results Blood pressure (both systolic and diastolic) and oxygen saturation of firefighters at rest showed a decreasing trend with increasing simulated altitude, while heart rate increased gradually with increasing altitude. The VO_{2, max} test in the hypoxic environment at 2 800 m showed that firefighters' systolic and diastolic blood pressure, as well as heart rate, increased with exercise intensity, whereas oxygen saturation decreased. Stepwise multiple linear regression analysis revealed that for each 1-year increase in age, 1 kg/m² increase in BMI, and 1 bpm increase in resting heart rate under normoxic, the VO_{2, max, 2 800} percentage of predicted VO_{2, max} changed by +0.54%, -0.86%, and -0.26%, respectively.

Conclusions Age, body mass index, and resting heart rate under normoxic conditions were significant predictors of an individual's endurance in hypoxic environments. These three indicators may serve as a composite criterion for selecting firefighters suited to high-altitude or hypoxic working conditions.