What Are Thresholds?
You may well have come across the terms ‘threshold’, ‘lactate threshold’ or ‘anaerobic threshold’ before. They’re the sort of phrases you hear coaches mention, or read about in magazines. In the world of sports science the concept of the threshold ‘phenomenon’ has been hotly debated over the last 30 or so years.
There has been a lot of discussion about the naming of these thresholds and whether clear breakpoints in the lactate/workrate relationships actually do exist.
Most commonly these thresholds are determined from assessing the changes in blood lactate concentration during an incremental exercise test - hence the term 'lactate threshold'.
If you have any questions about lactate thresholds or any aspect of triathlon training then please just ask us.
When your body uses carbohydrates as a fuel lactate is produced. This process is called anaerobic metabolism. When carbohydrate is metabolised, lactic acid is produced in the form of lactate ions and hydrogen ions. The greater the rate that carbohydrate is metabolised for energy, the greater the rate that lactate is produced.
In the early 1900s it was believed that lactate was a waste product occurring only during high intensity exercise. This view has been significantly challenged over the last 20 years. This is because aerobic and anaerobic glycolysis occur simultaneously, regardless of the intensity of exercise. The relative contribution of each process will vary depending on the intensity of exercise.
So at low intensities (plenty of oxygen available), aerobic metabolism will dominate, and the lactate produced from the small contribution of anaerobic metabolism will be cleared.
As the exercise intensity increases, the contribution of anaerobic metabolism to the production of energy increases, as less oxygen becomes available. More and more lactate will be produced, and eventually there will be more being produced than can be cleared.
So lactate is always produced, but when the exercise intensity is low enough, it is actually used as a fuel and therefore it does not accumulate.
When the rate of production exceeds the rate that it can be cleared (metabolised for further energy production and neutralised by other processes), lactate and hydrogen ions will accumulate in the blood and muscles. The accumulation of hydrogen ions makes the blood and muscle more acidic, which inhibits the functioning of the muscle, causing you to not be able to work as hard.
Hence lactate is associated with fatigue, without in itself causing fatigue.
Therefore the concentration of lactate in the blood gives an indication of the predominant type of energy metabolism being used. This gives an indication of your training status - the better you are able to use a higher proportion of fats rather than carbohydrate as fuel (therefore saving carbohydrates for later in the exercise or for higher intensity exercise) the lower your blood lactate concentration will be.
Nowadays the measurement of blood lactate levels during an incremental exercise test has become one of the main ways of assessing endurance performance. These tests usually determine the lactate thresholds or variations on this concept.
The term ‘threshold’ is commonly used to describe the point (or exercise intensity) when the energy source your body uses to fuel your activity changes significantly and measurably.
The proportion of these two fuels (fats and carbohydrates) that you use will depend on the intensity of the activity you are doing, and to a certain extent, the availability of these fuels. You have a much longer lasting supply of fats than carbohydrates, therefore the main aim of training for an endurance sport is to train your body to become better at using fats.
Blood lactate accumulation during a test where exercise intensity increases is often used to prescribe training intensities based on the 'lactate thresholds' as well as assessing endurance performance. Traditionally these two points were determined at set concentrations of lactate in the blood: 2 and 4mmol/l.
However a more individualised approach is now more common. The thresholds are generally determined by plotting blood lactate concentrations on a graph against workload (see below).
There are two transition points commonly used to assess training status and prescribe training. They can also be used to a certain extent to predict performance and racing intensities.
A downwards and/or rightwards shift in the lactate curve is generally accepted to indicate an improvement in endurance capacity. A shift in the opposite direction indicates a worsening in endurance capacity.
However interpretation of the data must be done with care. Low levels of carbohydrate stored in the muscles (seen when an athlete doesn’t consume enough carbohydrate following long, hard training sessions) means that the body won’t produce as much lactate as normal. This is because there isn’t enough carbohydrate available to be used as a fuel to result in much of an accumulation of lactate.
This is where a lot of the confusing terminology comes in, with people using the same term or phrase for these transitions to mean different things.
As mentioned, there are two typical breakpoints that are passed during incremental exercise. The first one is commonly called the aerobic threshold – so called because it marks the upper limit of exercise fuelled almost exclusively by aerobic metabolism. Exercise below or at this point can be maintained for hours.
Exercise intensities slightly above this threshold result in slightly higher concentrations of lactate in the blood, however this concentration stays at a constant level.
The highest intensity of exercise that results in a balance between the amount of lactate being produced and the amount being eliminated is the MLSS. Some call this the anaerobic threshold.
MLSS represents the upper border of constant load endurance training. Training at intensities above MLSS would be classed as interval training.
Between the first (aerobic/lactate) threshold and the second (anaerobic, MLSS) threshold is called by some the aerobic-anaerobic transition.
This is also referred to as the Lactate Threshold.
This is the point in exercise where lactate levels first start to rise above baseline. Ideally this will occur at a relatively high workload that would indicate a well-developed aerobic base. An adaptation to training which results in an improvement in base aerobic condition will be reflected by your lactate threshold occurring at a higher work load. This is due to an improved ability to burn fat as a fuel, saving carbohydrate stores.
How It Impacts On Performance:
The lactate threshold intensity can usually be sustained for around 3 hours, therefore if you are competing in an event that you will complete in around this time, then lactate threshold will be important for you.
How Do I Train It?
Training at or around lactate threshold intensity has been shown to be the best way to shift this point to a higher work load. Sessions would involve between 30 minutes and an hour, hour and a half of continuous exercise. See our Triathlon Training pages for more information.
This is also known as:
This is the point where there is a ‘sudden and sustained’ increase in blood lactate concentration.
Accumulation of lactate is associated with the onset of fatigue; therefore the higher the intensity this occurs at, the greater resistance you have to fatigue. This is the highest possible steady-state work intensity that can be maintained for a prolonged period of time.
Above this intensity you would begin to fatigue more rapidly. Like the lactate threshold, this can be improved with training. An increase in the exercise intensity at which the anaerobic threshold occurs could indicate an improvement in lactate buffering or lactate clearance.
How It Impacts On Performance:
The anaerobic threshold intensity can be sustained for around 30 - 60 minutes, so if you are competing in an event that will take you this duration to complete, then the anaerobic threshold is important for you.
How Do I Train It?
Continuous ‘tempo’ or ‘brisk’ running for 20 – 40 minutes at anaerobic threshold intensity. You can split the session into periods above and below the threshold intensity, see our Triathlon Training pages for more information.
MLSS, Maximal Lactate Steady State
This is the highest exercise intensity at which the production of lactate and its clearance are balanced.
Maximal Lactate Steady-State (MLSS), Lactate Threshold (LT) or Individual Anaerobic Threshold (IAT) have all been used synonymously to point to an almost physiological steady state.
The exercise intensity at which this occurs will be a key factor for performance in endurance based sports as an accumulation of lactate leads to muscle fatigue. An individual would be able to sustain this intensity for around 30 – 60 minutes.
The gold standard for determining MLSS is by performing several constant load trials of at least 30 minutes duration on different days. Blood lactate concentrations are monitored throughout the exercise.
The highest exercise intensity during which there is no increase in the blood lactate concentrations throughout the effort is the MLSS intensity.
This is not very practical so it is more common for athletes to have the second threshold determined as the point where there is a sudden and sustained rise in blood lactate levels during an incremental exercise test.
Onset of blood lactate accumulation. The name says it – the exercise intensity when lactate starts to accumulate in the blood. Essentially the same as MLSS.
Critical Velocity, Critical Power
These aren’t thresholds. Officially they are they are the highest speed or power output that you can sustain at MLSS (ie without an accumulation of lactate). However this term is increasingly being used to describe the highest speed/power output that can be sustained for any given duration – whether that be 3 minutes or 3 hours.
This term has been butchered since its original definition by Moder (1966). Officially Critical Power is a work rate that can be sustained indefinitely (i.e. not limited by the availability of energy). However many contemporary coaches and physiologists use this term to mean the highest work rate that can be sustained for a range of times.
Therefore you may hear people talk about ‘my CP60’. This basically means how much power you can sustain for 60 minutes. It will roughly equate to any of the other second threshold measures, particularly in swimming and cycling. If your race is going to last around 60 minutes it might be an interesting number to know and many of the software packages used for calculating load use this as a simple test that everyone can do to calculate a ‘threshold’ .
Whilst there is still a lot of confusion surrounding thresholds – how to interpret the data and what to call them – it is clear they relate to endurance performance. Therefore if the information is used correctly, knowing where your thresholds lie can help you train more precisely.
It must be remembered that the exercise intensity at which your thresholds occur will be different for running and cycling due to the different muscle mass involved.
For the sake of simplicity we refer to the two thresholds as Lactate Threshold 1 (LT1) (first or ‘aerobic’ threshold) and Lactate Threshold 2 (LT2) (second or ‘anaerobic’ threshold) in our other pages, not because we believe any term is actually more correct than any other, but using a number helps to avoid confusion about which comes first!
Got a question about lactate thresholds or your triathlon training?
Then ask us!