Effects of exercise interventions in hypoxic environment on cardiovascular function and maximal power output in obese or overweight individuals: a systematic review and meta-analysis

To compare the effects of normobaric hypoxic exercise versus normoxic exercise on improving cardiopulmonary and cardiovascular function and maximal power output in overweight and obese individuals, thereby providing evidence-based support for exercise prescription and public health interventions. Following the PRISMA guidelines, randomized controlled trials examining the effects of exercise interventions under hypoxic conditions on cardiopulmonary and cardiovascular function or exercise capacity in individuals with overweight or obesity were retrieved from databases comprising PubMed, the Cochrane Library, Ovid, Web of Science, Embase, and ClinicalTrials.gov. The search period extended from the inception of the databases to February 15, 2025. Stata was used to assess publication bias, heterogeneity, and data synthesis and generate funnel plots and forest plots. The DerSimonian–Laird random-effects model was applied for the meta-analysis. The I² statistic was used to quantify heterogeneity and subgroup, and sensitivity analyses were conducted to explore potential sources of heterogeneity and influencing factors. A total of 19 randomized controlled trials with 523 participants were included. A meta-analysis revealed that hypoxic training significantly enhanced maximal oxygen uptake (VO2max) and maximal power output (MPO) compared to normoxic training. The standardized mean differences (SMDs) were 0.42 (95% CI: 0.16–0.67, 95% PI: -0.10, 0.94, P < 0.01, I2 = 15.4%) for VO2max and 0.43 (95% CI: 0.01–0.85, 95% PI: -0.80,1.67, P < 0.05, I2 = 56.0%) for MPO. The corresponding weighted mean differences were 191.88 mL/min for VO2max (95% CI: 75.66–308.10; 95% PI: 31.68–352.08; P = 0.001) and 14.53 W for MPO (95% CI: 1.40–27.66; 95% PI: -3.51–32.57; P = 0.030). Subgroup analyses revealed that VO2max (SMD = 0.498, 95% CI: 0.077–0.919, P = 0.020, I2 = 0%) and MPO (SMD = 0.431, 95% CI: 0.012–0.851, P = 0.044, I2 = 0%) were significantly improved compared with the control group when the intervention duration exceeded 8 weeks. Additionally, significant improvements in VO2max were observed under the following conditions: fraction of inspired oxygen (FiO2) ≧ 15% (SMD = 0.420, 95% CI: 0.057–0.784, P = 0.024, I2 = 12.1%), training frequency of more than three sessions per week (SMD = 0.534, 95% CI: 0.002–1.065, P = 0.049, I2 = 0%), high-intensity protocols (SMD = 0.532, 95% CI: 0.108–0.956, P = 0.014, I2 = 0%), session duration of less than 45 min (SMD = 0.420, 95% CI: 0.047–0.793, P = 0.027, I2 = 0%), and high-intensity interval training (HIIT) as the intervention (SMD = 0.532, 95% CI: 0.108–0.956, P = 0.014, I2 = 0%). Female participants showed significantly greater improvements in VO2max compared to the control group (SMD = 0.571, 95% CI: 0.128–1.014, P = 0.012, I2 = 0%). Hypoxic exercise interventions effectively improved VO2max and MPO in individuals with overweight or obesity, with greater VO2max gains observed in women. Exercise interventions in hypoxic environments are recommended to last for longer than 8 weeks, with no more than three sessions per week of HIIT lasting less than 45 min.