Ventilatory thresholds are detectable using DFA-α1 at group level but not individual level during swimming, cycling and running

Background: Ventilatory thresholds (VT1 and VT2) determined from gas-exchange criteria during cardiopulmonary exercise testing (CPET) provide reference points for exercise-intensity prescription, but their routine use is limited in applied settings. Detrended fluctuation analysis alpha 1 (DFA-α1) has emerged as a potential non-invasive marker of physiological transitions during exercise. Objective: To quantify and compare DFA-α1 values against CPET-derived ventilatory thresholds and between exercise modes during constant-load swimming, cycling, and running in trained triathletes. Methods: Seventeen triathletes (13 men, 4 women) completed maximal incremental CPETs in swimming, cycling, and running, after which constant-load trials were undertaken at VT1 and VT2, as determined from CPET using standard ventilatory criteria. R-R intervals were recorded with a Polar V800 and Polar H10 and processed in Kubios HRV Scientific v4.2.0. DFA-α1 was calculated using a 120-s moving window with 5-s updates. Between-modality comparisons were performed using repeated-measures ANOVA. Results: At VT1, V˙ O2, heart rate, and PetCO2 differed by modality, whereas DFA-α1 did not differ significantly between swimming, cycling, and running (0.74 ± 0.30, 0.75 ± 0.21, and 0.65 ± 0.20, respectively; P = 0.456). At VT2, V˙ O2 and heart rate again differed by modality, whereas DFA-α1 showed no significant differences between modalities but wide between participant variability (0.42 ± 0.13, 0.37 ± 0.11, and 0.47 ± 0.13, respectively; P = 0.061). Conclusion: At the group level, mean DFA-α1 values were numerically close to previously proposed values for VT1 (∼0.75) and VT2 (∼0.50). However, the marked inter-individual dispersion across modalities limits the use of fixed DFA-α1 values for individual identification of VT1 and VT2. These findings indicate descriptive group-level correspondence rather than individual-level validity or agreement.