The effect of exercise training status during acute Hypoxia on substrate metabilism

Abstract

Substrate metabolism fluctuates at rest and during exercise, with further changes as exercise intensity increases. During hypoxia, the reduction in available oxygen (O2) will cause further alterations to substrate metabolism from the challenge that is placed on the metabolic pathways. It is currently unclear whether training status influences changes in substrate metabolism during exercise in hypoxia. The purpose of the study was to investigate the effect of training status during hypoxia on substrate metabolism at rest and during exercise. Twenty healthy male participants were used for the study; 8 untrained (20 ± 1.5 yr, 1.78 ± 0.08 m, 82.1 ± 11.2 kg, VO2max 32.6 ± 4.9 ml·kg-1·min-1), 8 endurance trained (28 ± 5 yr, 1.81 ± 0.06 m, 73.3 ± 7.5 kg, VO2max 46.4 ± 7.2 ml·kg-1·min-1) and 4 sprint trained (22 ± 3.3 yr, 1.83 ± 0.01 m, 74.8 ± 3.1 kg, VO2max 45.6 ± 1.9 ml·kg-1·min-1). Participants attended two separate laboratory visits. During the first visit a VO2max was completed on a supine tilt bike. The second visit comprised of four exercise stages lasting five minutes; rest, 30%, 40%, and 50% Wmax. Each of which was performed in normoxia (21% O2) and hypoxia (12% O2), which were separated by 45 minutes of rest in normoxia. Data for respiratory exchange ratio (RER) and minute ventilation (VE) were collected throughout each stage using breath by breath gas analysis on the Oxycon pro. A blood sample to measure lactate was taken in the last minute of each stage. A two-way repeated measures ANOVA was used to determine significance and a paired t-test was used to determine differences of RER, VE, blood lactate and heart rate between exercise conditions and training status groups. Analysis identified significant differences between the exercise intensities (p < 0.05) of all variables in both normoxia and during hypoxia, however no significance was found between the groups in any of the variables in either normoxia or hypoxia (p > 0.05). Differences between normoxia and hypoxia were seen in RER at rest (p = 0.001; p =0.041) and at 50% Wmax (p = 0.0006; p = 0.016) in endurance trained and untrained individuals respectively. There was a significant interaction for VE in normoxia (p = 0.018) and hypoxia (p = 0.005) with differences at 50% Wmax in untrained (p = 0.005) and enruance trained individuals (p = 0.002). A significant interaction was found for blood lactate during hypoxia (p < 0.0001) and during normoxia and hypoxia there were significant differences at rest and at 50% Wmax in all groups (p < 0.05). The findings indicate that RER increases during hypoxia at rest, and during exercise due to the greater challenge that is inflicted on metabolism.