Lactate Threshold

Lactate threshold (LT) is an exercise intensity identified from a systematic rise in blood lactate concentration during progressively harder exercise. At lower intensities, lactate is continuously produced and removed, and its blood concentration remains relatively stable. As exercise intensity increases, blood lactate eventually begins to rise above its previous level, producing a detectable transition in the lactate response .^1,2

The rise in blood lactate does not mean that exercising muscles have suddenly become anaerobic or run out of oxygen. Lactate is produced and used even when oxygen is readily available. Its concentration in blood reflects the balance between lactate appearance, including production and release by tissues, and lactate removal through oxidation or conversion into other metabolites. Increasing glycolytic activity during harder exercise contributes to the changes observed around lactate thresholds .²

Lactate threshold is usually determined during an incremental exercise test by measuring blood lactate at successive workloads. However, there is no single universally accepted method for defining or calculating it. Some methods identify an initial sustained increase above baseline, often referred to as the first lactate threshold (LT1), while others identify a later, steeper rise or use a fixed blood lactate concentration. These different methods can produce different threshold values and should not be treated as interchangeable .^1,3

Lactate threshold is related to, but distinct from, ventilatory threshold. Lactate thresholds are derived from blood lactate measurements, whereas ventilatory thresholds are identified from changes in ventilation and respiratory gas exchange. The corresponding transitions often occur near one another but are not physiologically or methodologically identical .^2,3