Zone 2 Training

Zone 2 training is defined as low-intensity exercise below the lactate threshold. ^[1] The lactate threshold marks the upper limit of moderate-intensity exercise and can be estimated from gas exchange during whole-body exercise, so training below it corresponds to the moderate-intensity domain. ^[2]

The rationale for Zone 2 training stems largely from observational data on elite endurance athletes, who perform large volumes of low-intensity training and possess high mitochondrial and fatty acid oxidative capacity. ^[1] When exercise is performed below the lactate threshold, oxygen uptake rises to a steady-state level and lactate production and elimination remain in equilibrium, whereas above it a slow component and progressive lactate accumulation appear. ^[3]

A 2025 narrative review critically examined the current evidence and concluded that it does not support Zone 2 training as the optimal intensity for improving mitochondrial or fatty acid oxidative capacity, arguing that higher intensities are critical to maximize cardiometabolic benefits, particularly at lower training volumes. ^[1] The framing of Zone 2 relative to the lactate threshold reflects a long-debated field, with a review locating 25 distinct lactate-threshold concepts divided into three categories, underscoring that the intensity anchor for Zone 2 is not standardized. ^[4]

The speed at lactate threshold integrates VO2max, running economy, and fractional utilization of VO2max and is the best physiological predictor of distance-running performance, which is why low-intensity work below that threshold is prominent in endurance training. ^[5]