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=What is Lactate?=
''Main article: [[Lactate]]''
At one time [[Lactate]] was viewed as a harmful waste product due anaerobic exercise, but research since the early 2000s has shown that Lactate is an intermediate fuel in the metabolism of carbohydrates. Muscles will burn Lactate in preference to Glucose, and will convert Lactate back to Glucose at rest. The level of Lactate in the blood is primarily dependent on exercise intensity. Note that Lactate forms Lactic Acid in the blood, and the terms are used interchangeablyrather like [[Heart Rate]]. Lactate is used as a fuel source by working muscles, and injecting extra lactate into the blood results in increased lactate metabolism and carbohydrate sparing<ref name="MillerFattor2002"/> without impairing performance<ref name="EllisSimmons2009"/>. Note that Lactate forms Lactic Acid in the blood, and the terms are used interchangeably.
=What is the Lactate Threshold?=
The Lactate Threshold (LT) is the point at which the lactate level in the blood will rise even if the work intensity is kept constant. This is sometimes referred to as the Anaerobic Threshold (AT), or the Onset of Blood Lactate Accumulation (OBLA), though the most accurate term is Maximal Lactate Steady State (MLSS). Even within the scientific community terminology is confusing<ref name="Binder-2008"/>. It is sometimes believed that the MLSS represents the maximum clearance of Lactate, but this may not be the case<ref name="EllisSimmons2009"/>. Note that Lactate is normally measured in the blood stream, so the Lactate level reflects the net of the muscles releasing and absorbing Lactate.
Lactate Threshold is important as it is an excellent good predictor of race performance<ref name="Billat-1996"/><ref name="Palmer-1999"/><ref name="Baldari-2000"/><ref name="Jones-2000"/><ref name="Lehmann-1983"/><ref name="Tanaka-1984"/>, and may be a better predictor than [[VO2max|V̇O<sub>2</sub>max]]<ref name="Allen-1985"/>. Lactate Threshold can be thought of as the percentage of VO2max that can be maintained for a protracted time<ref name="Costill-1973"/>, though it's not clear what the limiting factor is for exercise above the Lactate Threshold<ref name="Baron-2008"/>.=Lactate Threshold Training =''Main article: [[Tempo Runs]]'' There is good evidence that endurance training changes Lactate Threshold. However, the idea that training at threshold intensity, such as [[Tempo Runs]], is particularly effective has no evidence<ref name="Beneke-2011"/>"/><ref name="Guellich-2010"/>, and polarized training is a better approach<ref name="StögglSperlich2014"/><ref name="Muñoz-2014"/>. For trained athletes, Tempo runs are ineffective<ref name="Londeree-1997"/> and may actually be counterproductive<ref name="Evertsen-2001"/><ref name="Guellich-2010"/>. See [[Tempo Runs]] for more details. Detraining shifts will reduce the Lactate Threshold<ref name="Coyle-1985"/>, and Lactate levels can be higher at a given intensity after just a few days without training<ref name="Mujika-2001"/>, suggesting rapid detraining effects. =The Usefulness of Lactate Threshold=One of the primary goals of Lactate Threshold testing is to determine the correct pace for [[Tempo Runs]]. However, even if Tempo training is ineffective there are two good reasons for knowing your Lactate Threshold. Firstly, monitoring Lactate Threshold is a great way of evaluating the effectiveness of a training regime. Secondly, Lactate Threshold can be used to validate race pace goals. If your Lactate Threshold suggests a much faster race pace than you've been able to achieve, it suggests either a lack of resistance to muscular damage or a lack of mental fortitude. If the Lactate Threshold suggests a race pace that is slower than your target goal, it suggests you objective is wrong and you should aim for a slower finish time. This is especially important in the marathon, where "hitting the wall" is a common issue.
=Lactate Curve=
It is common to plot exercise intensity against lactate level to produce a blood lactate curve similar to the one below, showing an exponential rise in lactate level with intensity. It's generally accepted that a shift of the curve to the right indicates an improved athletic performance<ref name="Bosquet-2002"/><ref name="Yoshida-1990"/>, and training can improve performance because of this shift without a change in aerobic capacity ([[VO2max|V̇O<sub>2</sub>max]])<ref name="Acevedo-1989"/>. There is some limited evidence from radio-isotope studies in animals that a benefit of endurance training may be in Lactate clearance<ref name="Donovan-1983"/>. Note that above the Lactate Threshold the Lactate level is not at a steady state, but rises even though the intensity remains constant, so the typical curve that is shown is rather misleading. Some Lactate Curves are plotting Blood Lactate against time during an Incremental Power Test (see below), which is more reasonable, but can still be rather misleading.
[[File:LactateThreshold.png|none|thumb|500px|A blood lactate curve with lactate level plotted against intensity. Note that above the Lactate Threshold there is no fixed relationship between Lactate and work intensity, so the curve is misleading at best. ]]
=Determining Lactate Threshold=
There are various ways of determining the Lactate Threshold, each with their own problems.
Because MLSS is time consuming and expensive, a shortcut is often used to estimate MLSS by assuming that it occurs at a fixed Lactate Level (Fixed Blood Lactate Accumulation, or FBLA)<ref name="De SouzaGrossl2012"/>, unusually 4.0 mmol/l<ref name="Heck-1985"/> though sometimes 3.5 mmol/l<ref name="DenadaiFigueira2004"/><ref name="Denadai-2005"/>. However, while the MLSS may average around 4.0 mmol/l<ref name="Denadai-2005"/>, there are significant differences for individuals<ref name="Mamen-2009"/>, with variations between 3.0 and 5.5 in small sample sizes<ref name="Heck-1985"/> and has been shown to have a range as wide as 2.0 to 10.0 mmol/l<ref name="Faude-2009"/><ref name="Stegmann-1981"/>. This approach also typically uses a blood test, but in some sports (like running), the athlete has to pause to have a pinprick blood sample taken, further confusing the test<ref name="Heck-1985"/>. The term "Individual Anaerobic Threshold" (IAT) has been used to emphasize that the Lactate Threshold is specific to each individual rather than using a FBLA, though this can refer to a specific protocol for estimating MLSS<ref name="Stegmann-1981"/>. The Fixed Blood Lactate Accumulation is sometimes called "Onset of Blood Lactate Accumulation" (OBLA)<ref name="Mamen-2009"/>, a particularly misleading term in this context.
==Lactate Threshold Estimation From Lactate Patterns==
There have been several approaches to determining MLSS without the difficulty of the full protocol<ref name="Billat-1994"/><ref name="Harnish-2001"/><ref name="Palmer-1999"/><ref name="Tegtbur-1993"/><ref name="Dickhuth-1999"/><ref name="Urhausen-1993"/>, but their validity is limited<ref name="Kilding-2005"/><ref name="De SouzaGrossl2012"/><ref name="Beneke-1995"/><ref name="Jones-1998"/>. These approaches generally look for some pattern in the change of Lactate level.
For example, one approach called the "Lactate Minimum Speed Test" (LMST) uses an initial sprint to elevate blood lactate followed by an incremental power test<ref name="SoteroPardono2009"/><ref name="Sotero-2009"/><ref name="MiyagiLeite2013"/>. However, the effectiveness of the LMST is profoundly impacted by the starting speed of the incremental portion of the test<ref name="Carter-1999"/>and so the results may be coincidence<ref name="Carter-2000"/>. This is not entirely surprising given the initial sprint phase disrupts the metabolism<ref name="Carter-2000"/>.
Some trivial approaches have been tried, such as looking for a 1 mmol/l increase followed by another 1 mmol/l increase<ref name="CTS"/>. So for an athlete performing an incremental load test with [[Lactate]] readings of 1.7, 2.3, 2.6, 3.7, & 5.6 the conclusion would be their Lactate Threshold is 3.7 (3.7 is more than 1.0 more than 2.6 and followed by another increment of more than 1.0.) However, given that most portable Lactate meters have a Typical Error of 0.4-1.0 mmol/l<ref name="Tanner-2010"/>, a fractional error in the reading gives a different result. In the previous example, if the 2.6 reading was 2.8, then the Lactate Threshold would jump from 3.7 to 5.6.
Part of the problem with these approaches may be that MLSS may not represent the point of maximum lactate clearance<ref name="Beneke-2003-2"/>, as injecting additional lactate into the blood of athletes exercising above MLSS did not significantly increase lactate levels<ref name="EllisSimmons2009"/>.
Some of the tests could be "p-hacking", where the study looks at a sufficiently large number of variables that some correlation occurs randomly<ref name="HeadHolman2015"/>.
<ref name="Donovan-1983">CM. Donovan, GA. Brooks, Endurance training affects lactate clearance, not lactate production., Am J Physiol, volume 244, issue 1, pages E83-92, Jan 1983, PMID [http://www.ncbi.nlm.nih.gov/pubmed/6401405 6401405]</ref>
<ref name="Gleeson-1998">M. Gleeson, AK. Blannin, NP. Walsh, CN. Field, JC. Pritchard, Effect of exercise-induced muscle damage on the blood lactate response to incremental exercise in humans., Eur J Appl Physiol Occup Physiol, volume 77, issue 3, pages 292-5, Feb 1998, doi [http://dx.doi.org/10.1007/s004210050336 10.1007/s004210050336], PMID [http://www.ncbi.nlm.nih.gov/pubmed/9535593 9535593]</ref>
<ref name="Jones-1998">AM. Jones, JH. Doust, The validity of the lactate minimum test for determination of the maximal lactate steady state., Med Sci Sports Exerc, volume 30, issue 8, pages 1304-13, Aug 1998, PMID [http://www.ncbi.nlm.nih.gov/pubmed/9710874 9710874]</ref>
<ref name="CTS">The Performance Benefits of Lactate Threshold Testing and Training - CTS, http://trainright.com/the-performance-benefits-of-lactate-threshold-testing-and-training/, Accessed on 22 August 2015</ref>
<ref name="Tanner-2010">RK. Tanner, KL. Fuller, ML. Ross, Evaluation of three portable blood lactate analysers: Lactate Pro, Lactate Scout and Lactate Plus., Eur J Appl Physiol, volume 109, issue 3, pages 551-9, Jun 2010, doi [http://dx.doi.org/10.1007/s00421-010-1379-9 10.1007/s00421-010-1379-9], PMID [http://www.ncbi.nlm.nih.gov/pubmed/20145946 20145946]</ref>
<ref name="Tanaka-1984">K. Tanaka, Y. Matsuura, Marathon performance, anaerobic threshold, and onset of blood lactate accumulation., J Appl Physiol Respir Environ Exerc Physiol, volume 57, issue 3, pages 640-3, Sep 1984, PMID [http://www.ncbi.nlm.nih.gov/pubmed/6490453 6490453]</ref>
<ref name="Lehmann-1983">M. Lehmann, A. Berg, R. Kapp, T. Wessinghage, J. Keul, Correlations between laboratory testing and distance running performance in marathoners of similar performance ability., Int J Sports Med, volume 4, issue 4, pages 226-30, Nov 1983, doi [http://dx.doi.org/10.1055/s-2008-1026039 10.1055/s-2008-1026039], PMID [http://www.ncbi.nlm.nih.gov/pubmed/6654546 6654546]</ref>
<ref name="Allen-1985">WK. Allen, DR. Seals, BF. Hurley, AA. Ehsani, JM. Hagberg, Lactate threshold and distance-running performance in young and older endurance athletes., J Appl Physiol (1985), volume 58, issue 4, pages 1281-4, Apr 1985, PMID [http://www.ncbi.nlm.nih.gov/pubmed/3988681 3988681]</ref>
</references>
