Purpose:The aim of this study was to compare VO₂ kinetics during constant power cycle exercise measured using a conventional facemask (CM) or a respiratory snorkel (RS) designed for breath-by-breath analysis in swimming.Methods:VO₂ kinetics parameters—obtained using CM or RS, in randomized counterbalanced order—were compared in 10 trained triathletes performing two submaximal heavy-intensity cycling square-wave transitions. These VO₂ kinetics parameters (ie, time delay: td1, td2; time constant: τ₁, τ₂; amplitude: A₁, A₂, for the primary phase and slow component, respectively) were modeled using a double exponential function. In the case of the RS data, this model incorporated an individually determined snorkel delay (ISD).Results:Only td₁ (8.9 ± 3.0 vs 13.8 ± 1.8 s, P < .01) differed between CM and RS, whereas all other parameters were not different (τ₁ = 24.7 ± 7.6 vs 21.1 ± 6.3 s; A₁ = 39.4 ± 5.3 vs 36.8 ± 5.1 mL·min⁻¹·kg⁻¹; td = 107.5 ± 87.4 vs 183.5 ± 75.9 s; A₂' (relevant slow component amplitude) = 2.6 ± 2.4 vs 3.1 ± 2.6 mL·min⁻¹·kg⁻¹ for CM and RS, respectively).Conclusions:Although there can be a small mixture of breaths allowed by the volume of the snorkel in the transition to exercise, this does not appear to significantly influence the results. Therefore, given the use of an ISD, the RS is a valid instrument for the determination of VO₂ kinetics within submaximal exercise.