Standardized z-score visualization for identifying ventilatory threshold in incremental talk test

Purpose: Ventilatory threshold (VT) is an indicator of cardiopulmonary function used to prescribe exercise intensity. Although not accessible to most, gas exchange analysis is the gold standard to detect VT. Other estimation methods, such as heart rate (HR) deflection point, Talk Test (TT), Ratings of Perceived Exertion (RPE), are used despite the influence of subjective factors, individual fitness or scale interpretation. The aim is to develop a standardized visual method for identifying VT during incremental exercise. Methods: Young adult (13 males) performed a TT, consisting of 3-min warm-up (1% grade fixed) at comfortable speed with 1 km/h speed increases every 2-min. At the end of each stage subjects recited the ‘‘Olympic Oath’’ and were asked if ‘‘Could speak comfortably?’’ with 3 possible answers: yes, not sure, no. Test ended at 95%HRmax or fatigue. During each stage %HRmax and RPE were measured (internal load), while speed and stage as external loads. Equivocal (EQ) TT stage ‘‘not sure’’ was used to estimate VT. 6 stages were performed by each subject. To visually assess VT, subjects %HRmax and RPE were first averaged for each stage, resulting in stage-specific identifiers, as RPEX(STAGE N) and %HRX(STAGE N) where ‘‘N’’ represents the stage (1 through 6). Mean and Standard Deviation (SD) for these variables across all stages were calculated to establish a normalization baseline. Z-scores were computed for each stagespecific average using the formula Z = (X-Mean)/SD, where ‘‘X’’ represents the stage-specific identifier. A scatter plot combining Z-score trend lines of %HRmax and RPE in relation to each TT stage was designed with a centerline showing all stages, and two distinct polynomial lines representing Z-scores. Results: The lines were concurrently plotted to show curvilinear relationships (R2 = 0.99), which mirror the internal load responses over the TT, with an intersection between %HRmax and RPE Z-scores lines at the 5th stage. At the intersection, data points showed an average speed of 11 km/h, 86%HRmax and 5RPE, with 9 subjects providing an EQ answer. Conclusions: According to literature, VT might occur in the 80–90%HRmax range or RPE4-5. Given the intersection point among Z-scores lines and confirmation of the EQ during TT, it can be assumed that the estimated and plotted intersection might visually confirm VT. Findings suggest using standardized Z-scores lines plot as a graphical method to easily detect VT.