What is the difference between Anaerobic Threshold (AT), Lactate Threshold (LT) and Ventilatory Threshold (VT)?
Anaerobic Threshold (AT) was a term applied to the lactate inflection point, or the point at which the appearance of lactate in the blood accumulates faster that its rate of use. It was once thought (incorrectly) that a lack of sufficient oxygen to muscle shifted energy delivery to anaerobic metabolism, resulting in an increase in lactate production thus causing fatigue. Since lactate does not cause fatigue, nor does it determine anaerobic metabolism, the misnomer anaerobic threshold was rejected as a concept nearly two decades ago. Simply speaking, no “anaerobic” threshold exists.
Lactate Threshold (LT) is a more recent and descriptive term for the lactate inflection point described above. Due to the misconception about lactate as the source of fatigue, it was thought that the workload just below lactate accumulation in the blood reflected a maximum sustainable level of performance (typically measured as a one hour time trial). Despite the fact that LT is a more descriptive name for the lactate inflection point than AT, current research suggests that it tends to underestimate time trial performance. Perhaps more important to consider is that there are no fewer than four different established methods of measuring and interpreting LT. Since the exercise science field has not agreed upon a single method, and each method can produce a different set of results for a given athlete, LT has questionable reliability and accuracy in measuring performance.
Ventilatory Threshold (VT) describes the inflection point for ventilation during an incremental exercise test. Ventilation increases at about the same rate as oxygen consumption up to about 50 to 70 percent of VO2max (depending on one’s trained level). At this point (just beyond the ventilatory threshold) ventilation increases exponentially. Some researchers have identified two ventilatory thresholds. Although ventilation is not a limiter to performance, there is evidence suggesting that power at VT predicts average power for a 40km time trial. However, similar to LT tests, there are multiple VO2max test designs, and the validity of the results vary by test. More important to measuring performance and training application using a heart rate monitor, VT may not accurately and reliability predict time trial (threshold).