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Demystifying the lactate threshold

There aren’t many athletes who haven’t come across the phrase ‘lactate threshold’: it’s a commonly cited parameter in training articles from magazines, books, and online resources. These articles all explain how it’s a better predictor of performance in trained athletes than the maximal oxygen uptake and how it’s an important intensity to train at. But, underlying these principles is one presumption – that people really understand what it is, and more importantly where it lies in the range of exercise intensities.

If scientists are confused, what hope for the athlete and coach?

The phrase ‘lactate threshold’ means many different things to people. Ask a coach about the threshold and the one he / she talks of will probably occur at an intensity you can sustain for around an hour. Ask a sport scientist, and he / she will ask “which one?”! And here lies the issue. The original concept of a ‘threshold’ was popularised in the early 1970s with important work by the group of Karl Wasserman1, a forefather of modern exercise physiology. Essentially, Wasserman and colleagues described how when a person engages in progressively harder exercise, a point is reached where effort can no longer be sustained by aerobic sources alone. Concentrations of blood lactic acid rise and respiratory changes occur. However, what many scientists overlooked was how Wasserman and colleagues explained that this threshold was in fact secondary to one occurring at a lower intensity, the ‘lactate threshold’. There are numerous terms used to describe the lactic acid and respiratory responses to gradually increasing exercise intensity. Table 1 attempts to summarise those used in the science and coaching literature, and also splits them into groups according to where they lie along the intensity continuum.

Table 1: Common phrases associated with the ‘threshold’ response

Lower threshold

(40 – 60% of VO2max)

Upper threshold

(60 – 80% of VO2max)
Lactate threshold onset of blood lactate accumulation (OBLA)
Ventilatory threshold individual anaerobic threshold (IAT)
Aerobic threshold lactate turnpoint
Lactate minimum Maximal lactate steady state

 


The ‘real’ lactate threshold

Lactate_ThresholdBefore we explain why there are essentially two points of interest on the exercise intensity continuum, it’s probably worth explaining the protocol for LT determination. The test consists of successive stages of exercise on a treadmill, bicycle ergometer, rowing machine etc. Initially the exercise intensity starts very low (30- 40% of the VO2 max). Each stage generally lasts about 3 to 5 minutes. Near the end of each stage, heart rate is recorded, oxygen consumption is measured, and a sample of blood is withdrawn, using a needle prick of the finger or earlobe in order to determine blood lactate concentration. After each stage, the workload is increased and the steps repeated. After 6 stages or more, we would expect to achieve a blood lactate profile similar to that in the figure below. Our lactate threshold is the first sudden and sustained increase in blood lactate concentration – here occurring at 150W and a heart rate of 150bpm.

The LT falls between 40% (in sedentary people or patients) and 75% (elite athletes) of VO2max. Despite being a concept long associated with endurance performance, it is still hotly debated as to what causes the LT response: some scientists arguing its related to hypoxia (a lack of oxygen) in the muscle necessitating anaerobic metabolism and therefore lactic acid production; others suggesting it is related to the recruitment of the type II (fast twitch) muscle fibres that use the lactic acid producing system of glycolysis. You’ll find a more detailed account of the possible LT mechanisms in another of our PBscience factsheets.

 

So, what is the difference in the two thresholds

The second threshold is most correctly described as the ‘Maximal lactate steady state’ concept – MLSS is defined as the highest running speed or power output at which blood lactate concentration remains stable between 10 and 30 minutes of constant intensity exercise2 (see Figure on the right). We tend to observe this at intensities of 75 to 85% VO2max, again dependent on fitness levels. MLSS corresponds to intensities associated with 25 mile time trial performance or 10 mile running pace i.e. events of ~1 hour in duration. There is lactic acid in the blood, but it is elevated and stable - the athlete will be able to tell us subjectively that its hard, but they are still in control, just! As to what causes this phenomenon, again research is unclear. However, whereas the LT is probably fundamentally caused by lactic acid production, the MLSS represents the upper limit of the rate of blood lactate clearance. Working above MLSS will lead to blood lactate accumulation and is related to a fatiguing state.

Why is it important to clarify which threshold people are referring to?

Quite simply, if a coach prescribes training using the phrase ‘lactate threshold’, the athlete needs to understand what intensity this refers to. If confused terminology is in place, training sessions set as ‘at threshold’ could refer to an intensity we could hold for 3 to 4 hours (the first LT) or one only sustainable for 1 hour (MLSS). How these parameters are related to the exercise training zones is explained in another of our PBscience factsheets.

How do I have my LT and second threshold measured?

MLSSThe lactate threshold, along with VO2max, is the most common of lab tests you can have performed. As described above, the protocol is quite straight forward – the hardest part is for the sport scientist to interpret where your LT is on the blood lactate / power graph: not all graphs give a nice, clear LT! It is very common for gas analysis to be performed during these tests too, as by looking at the respiratory data can help the sport scientist pinpoint the LT. It also allows an indirect measure of the second threshold without the need to complete a series of 30 minute trials to determine the MLSS (see figure right).

In practise it is almost unheard of for an athlete to have their MLSS identified in an applied setting. Much more useful is to use the concept of the functional threshold power (FTP) as popularised by Coggan and Allen in 'Training and Racing with a power meter', or in the lab by using gas exchange criteria to identify the second threshold (more specifically the respiratory compensation point) during a ramp test.

How can I use this data in my training?

Once you have had the tests done, the sport scientist can provide the power output and associated heart rate at which your LT occurs. Being the upper boundary of zone 2, it’s a very important marker for your training, and indeed, is often the hinge upon which the rest of your training zones can be structured.

 


REFERENCES

1.   Wasserman, K. et al. J Appl Physiol 1973, 35, 236-243.

2.   Philp, A. et al. Int J Sports Med 2008, 29, 475-479.

 

 

Lower threshold

(40 – 60% of VO2max)

Upper threshold

(60 – 80% of VO2max)

Lactate threshold

onset of blood lactate accumulation (OBLA)

Ventilatory threshold

individual anaerobic threshold (IAT)

Aerobic threshold

lactate turnpoint

Lactate minimum

Maximal lactate steady state

 
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