The two key lactate thresholds are commonly called LT1 and LT2. The first threshold, LT1, is the top of Zone 2 (in the five-zone model). It’s defined as, “the lowest intensity at which there is a sustained increase in blood lactate concentration above resting values.” A male professional cyclist weighing around 70kg is typically able to sustain around 300W at LT1 and can churn out this intensity for upwards of three hours. LT2 is reached at the top of Zone 4 and is often referred to as the lactate turnpoint. This is the point beyond which lactate accumulates rapidly. It roughly corresponds to FTP intensity. LT1 is often referred to as ‘aerobic’ and LT2 as ‘anaerobic’, which is a hangover from earlier, more rudimentary understanding.