The Effects Of Exercise Training In Hyperoxia Compared To Normoxia On Cardiorespiratory Fitness: A Meta-analysis

Abstract

PURPOSE: Previous studies have indicated that supplemental oxygen (i.e. hyperoxia) may acutely enhance exercise performance, providing benefits for patients with limited physical capacity. However, the evidence for superior long-term adaptations of regular hyperoxic exercise in clinical populations is limited. Therefore, this systematic review and meta-analysis aimed to evaluate the effects of chronic exercise in hyperoxia compared to normoxia in patients diagnosed with chronic diseases. METHODS: Databases were systematically searched for randomized controlled trials in accordance with PRISMA until May 20th, 2019. Eligibility criteria included adult patients with various chronic diseases (i.e. cardiovascular, pulmonary, neurological, metabolic, musculoskeletal or cancer) engaging in regular supervised exercise training in hyperoxia compared to an exercising normoxic control group. The outcome of interest included maximal power output (PO), peak oxygen consumption (VO2peak) and maximal distance in the 6-minute walk test (6MWD). Standardized mean differences (SMD) were calculated and a random-effects model was used to pool effect sizes using R (3.6.1). RESULTS: Out of the identified 4038 studies, 11 articles were deemed eligible. A total of 132 patients (64.3 ± 3.2 yrs., 36% women) and 131 patients (64.9 ± 3.6 yrs., 33% women) were included in hyperoxia and normoxia groups, respectively. The majority of patients were diagnosed with chronic obstructive pulmonary disease (COPD, 94.1%) while 18 patients were diagnosed with coronary artery disease. The average duration of interventions was 8.9 ± 5.1 weeks. The observed effects for PO (SMD -0.33; 95% CI -0.67, 0.01; p = 0.06), VO2peak (SMD -0.24; 95% CI -0.54, 0.05; p = 0.11) and 6MWD (SMD -0.21; 95% CI -0.78, 0.36; p = 0.46) showed no statistical significant difference between the two conditions. CONCLUSION: There is no evidence for beneficial chronic adaptations in cardiorespiratory fitness, when exercise is performed in hyperoxia. However, the studies to date have only examined patients diagnosed with COPD and coronary artery disease. Future studies should identify the optimal dose-response mechanisms to bridge the gap between acute responses and chronic adaptations in hyperoxic exercise.