Nasal breathing (NB) during aerobic exercise has gained attention due to its potential benefits to physical performance and health adaptations. However, it is unclear how an NB-induced increase in the partial pressure of CO2 (PetCO2) affects the enzymatic activity of glutathione peroxidase (GPX). PURPOSE: To determine the activity of GPX after 1-month of transient hypercapnic training induced by NB. METHODS: Fourteen males (age = 20.57 ± 1.22 yrs) were randomized to either the NB (n = 8) or combined breathing (CB, n = 6) group. Participants performed supervised aerobic training 4 times per week at ~70% of VO2max for one month. During baseline (V1) and post-intervention (V2) visits, participants completed a maximal aerobic exercise test (VO2max) on a recumbent bike and plasma samples were collected at pre- and immediately post-VO2max. Plasma GPX enzymatic activity was examined at 1-minute intervals from zero to 8 minutes following NADPH oxidation. A Pearson correlation analysis examined the relationship between respiratory performance during the VO2max test. A one-way ANOVA was utilized to examine respiratory differences between the NB and CB groups. RESULTS: The post-exercise GPX enzymatic activity was negatively associated [r(6) = -0.850, p = 0.007] with PetCO2 at 100% VO2max during V1 only in the NB group. Moreover, there was a significant difference (p = 0.013) in PetCO2 between the NB (31.59 ± 4.18 mmHg) and CB (25.65 ± 3.17 mmHg) groups at 100% VO2max during V1, where the post-exercise GPX activity of the NB (130.85 ± 25.28 nmol/min/mL) and CB (125.22 ± 23.47 nmol/min/mL) groups showed an apparent difference although it did not reach statistical significance. At V2, both NB (141.35 ± 33.04 nmol/min/mL) and CB (139.23 ± 30.42 nmol/min/mL) significantly increased (p = 0.039) the post-exercise GPX activity from their respective V1 values. Lastly, the association between post-exercise GPX activity and PetCO2 seen during V1 in the NB group was no longer present at V2, suggesting a potential adaptation to the training. CONCLUSION: Though bouts of transient hypercapnic aerobic exercise might negatively affect GPX activity, we present preliminary evidence indicating that the potential link between an increased PetCO2 and GPX inhibition may be blunted or no longer a factor of concern following 1-month of NB training.



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