Dose-response relationship of normobaric hypoxia training on body composition and metabolic health in obese adults: a systematic review and meta-analysis.

backgroundNormobaric hypoxia training (NHT) has emerged as a potentially superior exercise intervention for obesity management, theoretically offering enhanced metabolic stress and body composition benefits compared to normoxic exercise. However, optimal dose-response parameters remain undefined, limiting clinical translation and standardization of hypoxic exercise protocols.

objectiveTo comprehensively investigate dose-response relationships between NHT parameters and body composition/metabolic outcomes in adults with obesity through systematic review and meta-analysis.

methodsA systematic search of five databases (PubMed, Web of Science, Scopus, SPORTDiscus, CINAHL) was conducted from January 2014 to June 2025. Inclusion criteria comprised randomized controlled trials comparing NHT versus normoxic exercise in adults with BMI ≥ 25 kg/m². Primary outcomes included body weight, body fat percentage, BMI, fat mass, and waist circumference. Random-effects meta-analysis and univariate/multivariate meta-regression were employed for dose-response modelling. Dose parameters included fractional inspired oxygen (FiO₂), session duration, training frequency, intervention duration, and composite hypoxia dose scores.

resultsTen studies involving 301 participants were included. Contrary to theoretical expectations, NHT demonstrated no superior body composition benefits compared to normoxic exercise across primary outcomes: body weight (MD = 0.12 kg, 95% CI: -1.99 to 2.22, p = 0.89), body fat percentage (MD = 0.21%, 95% CI: -3.00 to 3.41, p = 0.87), BMI (MD = -0.34 kg/m², 95% CI: -0.16 to 0.85, p = 0.15), and waist circumference (MD = -1.26 cm, 95% CI: -9.38 to 6.87, p = 0.66). Fat mass increased in NHT groups (MD = 1.10 kg, 95% CI: 0.24 to 1.95, p = 0.02). None of the primary outcomes achieved pre-defined clinical significance thresholds. Comprehensive dose-response meta-regression examining six hypoxia parameters (FiO₂, session duration, frequency, intervention weeks, total exposure hours, composite dose score) revealed no statistically significant relationships with any body composition outcome (all p > 0.05, all R² = 0.0-15.5%). Moderate multicollinearity among dose variables (r = 0.688-0.995, max VIF = 6.45) precluded reliable multivariate modelling, though univariate analyses consistently demonstrated null dose-response effects across all parameter-outcome combinations, indicating absence of clear dose-response gradients within examined ranges. NHT showed a non-significant trend toward improved cardiovascular fitness (VO₂peak: MD = 1.43 mL/kg/min, 95% CI: -0.86 to 3.72, p = 0.16) though with moderate heterogeneity across studies (I² = 62%).

conclusionsThis systematic review and meta-analysis found no evidence that normobaric hypoxia training produces superior body composition outcomes compared with equivalent normoxic exercise in adults with obesity. The absence of superior body composition benefits, combined with paradoxical dose-response relationships and increased intervention complexity, suggests that NHT cannot be recommended as a superior alternative to conventional exercise training for obesity treatment. The non-significant trend toward cardiovascular benefits with inconsistent responses across studies indicates that further research is needed to determine whether NHT may have value for specific applications focused on aerobic capacity enhancement. These findings emphasize the importance of rigorous evidence evaluation before widespread implementation of novel exercise interventions.