Robustness and Validity of Ventilatory Parameters of the Tymewear Vital Strap Pro: A Comparative Study with the VO₂ Master across Different Exercise Intensities and Breathing Routes

Background. The Tymewear Vital Strap Pro (TWP) is a wearable device measuring respiratory frequency (RF) and an internal dimensionless parameter named 'circumference change', reflecting the amplitude of thoracic expansion. Within the Ventilatory Strategies Training (VST) program, the ability of the circumference change to estimate true tidal volume (Tv) and its sensitivity to breathing route (nasal vs. oral) had not yet been rigorously evaluated. Objectives. (1) Validate RF-TWP against the VO₂ Master via Bland-Altman analysis. (2) Characterize the circumference change-RF and circumference change-Tv relationships. (3) Quantify the effect of nasal vs. oral breathing on the circumference change. (4) Propose a Tv prediction model. Methods. An elite athlete performed an incremental test on a cycle ergometer (calibration, VT2, all-out) with simultaneous TWP and VO₂ Master measurements. A VT1 condition with pure nasal and oral breathing was compared. 16 measurement pairs and 2 oro-nasal conditions were analyzed using regressions, Bland-Altman analysis, and multiple regression. Results. RF-TWP showed near-perfect agreement with reference RF (r = 0.9996; bias = −0.10 bpm; LoA: [−0.55; +0.35]). Nasal breathing produced a significantly higher circumference changethan oral breathing at equivalent intensity (72.8 vs. 61.2; Δ = +11.5; +18.8%), as did the TIDAL signal (289 vs. 267; Δ = +8.2%). The bivariate circumference change+RF model explained 54% of Tv variance (R² = 0.54; RMSE = 0.20 L). Conclusion. The TWP measures RF with exceptional precision. The circumference change is strongly influenced by breathing route, constituting a differential nasal/oral marker applicable within the VST framework. These findings open perspectives on differential respiratory biomechanics and personalized ventilatory training prescription.