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Common physiological terms

This is a listing of common terminology and definitions used in the physiological and metabolic space. 


(Maximal Lactate Steady State): the highest blood lactate concentration (MLSSc) and work load (MLSSw) that can be maintained over time without a continual blood lactate accumulation (1)

Aerobic Threshold

the intensity at which blood lactate increases above resting levels. This is the point at which your anaerobic energy system begins to contribute (slightly) more to overall energy production. Often used interchangeably with VT1 or LT1. 

Anaerobic Threshold

the level of work or Oxygen consumption just below the point at which metabolic acidosis and the associated changes in pulmonary gas exchange occur (Wasserman et al., 1973). It represents the transition during which anaerobic means of energy supply becomes important during exercise. (2)

Ventilatory Threshold 1

a marker of intensity that can be observed in a person's breathing at a point where lactate begins to accumulate in the blood. As the intensity of the exercise begins to increase, VT1 can be identified at the point where the breathing rate begins to increase. (3)

Lactate Threshold 1

the lowest intensity at which there is a sustained increase in blood lactate concentration above resting values. (4)

Ventilatory Threshold 2

VT2 is the second threshold (above Vt1) which the rhythmic and controlled breathing pattern tends to break down, and an athlete is under significant stress. This threshold can also be associated with what has been called an anaerobic threshold or lactate threshold and is highlighted with a large increase in minute ventilation.

Lactate Threshold 2

the intensity that causes a rapid increase in blood lactate indicating the upper limit of equilibrium between lactate production and clearance. This can sometimes occur around 4 mmol/l, but this range can vary from person to person. Also commonly called the anaerobic threshold. (5)

VO2 max

VO2 max, or maximal oxygen consumption, refers to the maximum amount of oxygen that an individual can utilize during intense or maximal exercise. This measurement is generally considered the best indicator of cardiovascular fitness and aerobic endurance. (6)


1. Billat VL, Sirvent P, Py G, Koralsztein JP, Mercier J. The concept of maximal lactate steady state: a bridge between biochemistry, physiology and sport science. Sports Med. 2003;33(6):407-26. doi: 10.2165/00007256-200333060-00003. PMID: 12744715.

2. Wasserman K, Whipp BJ, Koyl SN, Beaver WL. Anaerobic threshold and respiratory gas exchange during exercise. J Appl Physiol. 1973 Aug;35(2):236-43. doi: 10.1152/jappl.1973.35.2.236. PMID: 4723033.

3. Reybrouck T, Ghesquiere J, Weymans M, Amery A. Ventilatory threshold measurement to evaluate maximal endurance performance. Int J Sports Med. 1986 Feb;7(1):26-9. doi: 10.1055/s-2008-1025730. PMID: 3082780.

4. Faude O, Kindermann W, Meyer T. Lactate threshold concepts: how valid are they? Sports Med. 2009;39(6):469-90. doi: 10.2165/00007256-200939060-00003. PMID: 19453206.

5. Ghosh AK. Anaerobic threshold: its concept and role in endurance sport. Malays J Med Sci. 2004 Jan;11(1):24-36. PMID: 22977357; PMCID: PMC3438148.d

6. Hawkins MN, Raven PB, Snell PG, Stray-Gundersen J, Levine BD. Maximal oxygen uptake as a parametric measure of cardiorespiratory capacity. Med Sci Sports Exerc. 2007 Jan;39(1):103-7. doi: 10.1249/01.mss.0000241641.75101.64. Erratum in: Med Sci Sports Exerc. 2007 Mar;39(3):574. PMID: 17218891.

1. Billat Reference
Wasserman 2
VO2 max
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