Restricted nasal-only breathing stimulates ventilatory efficiency during low intensity training but does not avoid training intensity fluctuation

INTRODUCTION: Low-intensity endurance training is frequently performed at gradually higher training intensities than intended, resulting in a shift towards threshold training. By restricting oral breathing and only allowing for nasal breathing this shift might be reduced and ventilatory efficiency may be trained.
METHODS: N = 19 physically healthy adults (3 females, age: 26.5 ± 5.1 years; height: 1.77 ± 0.08 m; body mass: 77.3 ± 11.4 kg; V̇ O2peak: 53.4 ± 6.6 ml·kg−1·min−1) performed two 60 min sessions of self-paced low-intensity cycling with breathing restriction (nasal-only breathing; induced by a strip of tape applied over the mouth) and without restrictions (oro-nasal breathing) in a randomized order. During these sessions, heart rate, respiratory gas exchange data and power output data were recorded continuously. Furthermore, capillary blood lactate was obtained every ten minutes (T10-T60).
RESULTS: No significant condition x time-effects were found for power (F(1.5, 22.7) = 1.42, p[GG] = 0.26, ηp2 = 0.09) and cadence (F(3.0, 44.7) = 2.27, p[GG] = 0.09, ηp2 = 0.13). For blood lactate concentrations, a significant and large condition x time-interaction effect was found (F(3.2, 57.1) = 3.61, p[GG] = 0.02, ηp2 = 0.17) with lower values during the nasal-only compared to the oro-nasal breathing condition towards the end of the session (T50: 1.21 ± 0.52 vs. 1.48 ± 0.59 mmolꞏl-1, p = 0.01, SMD = 0.49 & T60: 1.21 ± 0.47 vs. 1.45 ± 0.52 mmolꞏl-1, p = 0.02, SMD = 0.48). VO2 showed significant and large main effects for both time (F(1.7, 31.1) = 5.73, p[GG] = 0.01, ηp2 = 0.24) and condition (F(1, 18) = 5.49, p = 0.03, ηp2 = 0.23), indicating higher values for the oro-nasal training session. In terms of gross efficiency, simple main effect analysis for time revealed large effect sizes (F(1.9, 29.2) = 37.9, p < 0.001, ηp2 = 0.72). Although main effect analysis for condition did not show statistical significance (F(1.0, 15.0) = 3.7, p = 0.075, ηp2 = 0.20), pairwise comparison between time points indicated small to moderate effects with higher values for the nasal-only condition (0.24 ≤ SMD ≤ 0.31). Nevertheless, heart rate based calculations of the time in training zones did not reveal significant effects (Zone 1: (F(1, 18) = 0.03, p = 0.85, ηp2 = 0.00); Zone 2: (F(1, 18) = 0.14, p = 0.71, ηp2 = 0.01); Zone 3: (F(1, 18) = 0.19, p = 0.67, ηp2 = 0.01).
CONCLUSION: Although nasal-only breathing seems to stimulate ventilatory efficiency, it does not prevent participants from performing low-intensity training at higher intensities than intended. Longitudinal studies are warranted to evaluate longitudinal responses of changes in breathing patterns.