Ventilatory threshold : VT1 and VT2
LoadTwo respiratory breakpoints delimiting the three main intensity zones, detectable without blood draws using the talk test.
VT1 (first ventilatory threshold) corresponds to the onset of significant lactate accumulation: ventilation accelerates, conversation becomes difficult : the 'talk test' reveals VT1: you can still say 3-4 words per exhalation. VT2 (second ventilatory threshold, respiratory compensation point) marks CO₂ rising sharply: hyperventilation, no conversation possible. Between VT1 and VT2 = the 'threshold' zone (tempo/sweetspot). Ventilatory and lactate thresholds are close but not identical: gas analysis is lab-based, the talk test is field-based.
In TriPaced:
In TriPaced, VT1 corresponds to the upper boundary of Z2 (moderate aerobic) and VT2 to the upper boundary of Z4 (threshold). These thresholds are calculated from your FTP and HRmax. Most long sessions in base phase target Z2 : you should be able to speak in full sentences.