High-intensity exercise has more beneficial effects than lower intensities, but exercise above the lactate (La-) threshold (LT) accumulates muscle metabolites, including La-, that causes fatigue. This must be inhibited to facilitate further exercise. Active rather than passive recovery is more effective for this purpose, but no optimal intensity of active recovery has yet been established. Therefore, the aim of this study was to identify the optimal intensity of active recovery for La- removal relative to the LT. 24 men aged 18-30 years volunteered. Initially, subjects (n=6) ran 5-minute exercise bouts to raise blood [La-] to ~3.9±0.3mM (Mean±SEM), followed by active recovery intensities ranging 100-0% (rest) of the LT running velocity (VLT). This showed that active recovery at 80-100% VLT caused a faster fall in blood [La-] than recovery intensities <60% VLT, as measured by repeated La- recordings (p<0.05, repeated measures general linear model) and as determined by higher peak La- removal rates and shorter time constants (p<0.05 for both comparisons, 1-way ANOVA). In a different set of experiments (n=6), similar intensity-dependence of active recovery and La- removal was also confirmed after raising initial blood [La-] to ~10mM by 30-second all-out exercise bouts. Next, we investigated this phenomenon during and after high-intensity interval training sessions utilising 4-minute high-intensity running bouts (ON-transients) that were separated by 4-minute active recovery periods (OFF-transients). Firstly, we established the highest sustainable ON-transient intensity during a 4×4-minute interval training protocol (n=6). Running at 95% of maximal oxygen uptake (VO2max) was the highest intensity at which the protocol could be completed, whereas at 100% VO2max, only ~40% of the interval protocol could be sustained until intensity dropped (p<0.05, 1-way ANOVA). In a final set of experiments, subjects (n=5, 6 were recruited, but one withdrew), subjects ran interval training protocols with 4-minute ON-transients at 95% VO2max interspersed by 4-minute OFF-transients at active recovery intensities ranging 70-100% VLT. First, the interval training protocol resulted in blood La- accumulating to >7mM. However, none of the active recovery intensities removed La- during the OFF-transients. In fact, prolonged recovery after the intervals was required to remove [La-], during which active recovery at 90% VLT had a faster peak rate of La- removal (12±1%/min vs 6±1%/min; p<0.05, 1-way ANOVA), whereas the time constant tended to be smaller (6±2 vs 15±5 minutes; p=0.065). In conclusion, this suggests that La- removal during active recovery is intensity-dependent, with peak efficiency at or close to VLT. However, during interval training, extended recovery periods are required to fully remove La-, though 4-minute recovery periods may limit accentuated La- accumulation.