Measuring Blood Lactate
Resource Page on Measuring Blood Lactate with Tim Egerton
Measuring Blood Lactate
INTRODUCTION
Measuring blood lactate is of interest to coaches, athletes and researchers. It can help us to assess the effectiveness of endurance training programmes. However, there are a number of different blood lactate variables that can be measured. There are also varying methods of measurement. This resource page provides a critical analysis of methods commonly used for the measurement of various blood lactate variables.
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Measuring Blood Lactate
Increasing the ability to perform repeated muscular actions for an extended duration of time is a goal of many training programs. Endurance performance is largely explained by three key factors: aerobic capacity, lactate threshold, and work economy. A great deal of research has therefore been devoted to the study of changes in measures in these areas in response to different interventions. Exercise scientists have developed many ways of measuring these variables and each has strengths and weaknesses, as well as different degrees of accuracy.
What does this page provide?
This page explains what methods for studying changes in lactate threshold are available, when they are used, why they are used, and how accurate they are. By the end, you will be able to critically appraise studies investigating these areas and understand their individual strengths and weaknesses.
Identifying key concepts - Measuring Blood Lactate
The following terms and concepts are key for an understanding of how lactate threshold is measured:
1. Anaerobic Threshold – this is the term used to describe the exercise intensity at which a sudden increase in carbon dioxide production is seen.
2. Blood lactate – this is the content of lactate in the blood and is the balance between muscle lactate production and lactate clearance.
3. Onset of Blood Lactate Accumulation (OBLA) – this is the minimum exercise intensity at which a rise, rather than a fall, in blood lactate occurs when that exercise intensity is maintained over an extended period of time.
4. Lactate Threshold – this is the exercise intensity at which blood lactate rises above its resting value.
5. Lactate Turn-point – this is the point at which a sudden and sustained increase in blood lactate occurs during incremental exercise.
6. Maximum Lactate Steady State (MLSS) – this is the highest power output at which the increase in blood lactate is less than 1.0mM/L across the last 20 minutes of a series of 30-minute trials.
7. Respiratory Exchange Ratio (RER) – this is the ratio of carbon dioxide production to oxygen consumption.
8. Ventilatory Breakpoint – this is the exercise intensity at which a disproportionate increase in ventilation occurs in an attempt to clear excess Carbon Dioxide.
MEASURING BLOOD LACTATE
Lactate Turn-point is defined as the point at which a sudden and sustained increase in blood lactate occurs during incremental exercise. It is determined through the identification of breakpoints in the lactate curve during incremental exercise tests. During an incremental exercise test, blood lactate initially remains close to its resting value. However, at a particular exercise intensity blood lactate rises above the resting value. The exercise intensity at which this occurs is called the Lactate Threshold.
The increase in blood lactate above resting levels that occurs at the Lactate Threshold is not a sustained increase. That is, if this exercise intensity were to be maintained for a prolonged period of time, blood lactate readings will remain fairly level. However, there is a second breakpoint in the lactate curve at a higher intensity during an incremental exercise test. This second increase in blood lactate is sudden. Moreover, if this higher exercise intensity is sustained for a prolonged period of time then we would see a continued increase in blood lactate readings. The exercise intensity at which this second breakpoint occurs is called the Lactate Turn-point.
Maximum Lactate Steady State
Lactate Turn-point provides a good approximation of the work rate or speed at the Maximum Lactate Steady State (MLSS) (Smith & Jones, 2001; Pringle & Jones, 2002). MLSS is the highest power output at which the increase in blood lactate is less than 1.0mM/L across the last 20 minutes of a series of 30-minute trials (Pringle & Jones, 2002). The assessment of MLSS is considered to represent the gold standard in terms of measuring the dynamics of blood lactate accumulation during exercise. However, it is a time and labour intensive method and so it is rare for it to be directly measured. Furthermore, running speed at Lactate Turn-point has been shown to predict endurance running performance with considerable accuracy (Jones, 2006). As such, Lactate Turn-point represents a valid and informative means of assessing the efficacy of endurance training interventions.
Onset of Blood Lactate Accumulation (OBLA)
The Onset of Blood Lactate Accumulation (OBLA) is the minimum exercise intensity at which a rise, rather than a fall, in blood lactate occurs when that exercise intensity is maintained over an extended period of time. Specifically, OBLA is determined by identifying the speed or power output that produces a lactate reading of 4mM/L during an incremental exercise test.
Lactate Turn-point
Lactate Turn-point is defined as the point at which a sudden and sustained increase in blood lactate occurs during incremental exercise. It is determined through the identification of breakpoints in the lactate curve during incremental exercise tests. During an incremental exercise test, blood lactate initially remains close to its resting value. However, at a particular exercise intensity blood lactate rises above the resting value. The exercise intensity at which this occurs is called the Lactate Threshold.
The increase in blood lactate above resting levels that occurs at the Lactate Threshold is not a sustained increase. That is, if this exercise intensity were to be maintained for a prolonged period of time, blood lactate readings will remain fairly level. However, there is a second breakpoint in the lactate curve at a higher intensity during an incremental exercise test. This second increase in blood lactate is sudden. Moreover, if this higher exercise intensity is sustained for a prolonged period of time then we would see a continued increase in blood lactate readings. The exercise intensity at which this second breakpoint occurs is called the Lactate Turn-point.
Approximation of Maximum Lactate Steady State
Lactate Turn-point provides a good approximation of the work rate or speed at the Maximum Lactate Steady State (MLSS) (Smith & Jones, 2001; Pringle & Jones, 2002). MLSS is the highest power output at which the increase in blood lactate is less than 1.0mM/L across the last 20 minutes of a series of 30-minute trials (Pringle & Jones, 2002). The assessment of MLSS is considered to represent the gold standard in terms of measuring the dynamics of blood lactate accumulation during exercise. However, it is a time and labour intensive method and as such it is rare for it to be directly measured. Furthermore, running speed at Lactate Turn-point has been shown to predict endurance running performance with considerable accuracy (Jones, 2006). As such, Lactate Turn-point represents a valid and informative means of assessing the efficacy of endurance training interventions.
Lactate Threshold
During an incremental exercise test, blood lactate initially remains close to its resting value. However, at a particular exercise intensity (or, more properly, a particular metabolic rate), blood lactate rises above the resting value (Jones et al., 1999). The exercise intensity at which this occurs is called the Lactate Threshold. It is possible to predict endurance running performance with some accuracy from running speed at lactate threshold (Jones, 2006). Lactate Threshold can also explain inter-individual differences in time-to-exhaustion at vVO2max (Billat & Koralsztein, 1996). As vVO2max is another variable that is known to accurately predict endurance performance, there would appear to be real value in looking at these two variables together when evaluating the efficacy of a training intervention.
Anaerobic Threshold
When exercise reaches a certain level of intensity, oxygen delivery to the muscles is no longer able to support the energetic demands of exercise and so more energy is derived from glycolysis. This results in the increased production of lactic acid, which is then broken down into various by-products. One of these by-products is carbon dioxide. This has led to the notion that a sudden increase in carbon dioxide during exercise represents a shift towards anaerobic metabolism. As a result the term Anaerobic Threshold was coined to describe this purported phenomenon.
Respiratory Exchange Ratio
The Respiratory Exchange Ratio (RER) was originally used to determine the anaerobic threshold. The RER is the ratio of carbon dioxide production to oxygen consumption, and so an increase level of carbon dioxide production would be expected to result in an increased RER. However, this method is now outdated. Current best practice for the determination of Anaerobic Threshold is the identification of the point at which the ventilatory equivalent for oxygen shows a sudden increase while the ventilatory equivalent for carbon dioxide remains relatively stable. The ventilatory equivalent for oxygen is the ratio of ventilation to oxygen consumption. Similarly, the ventilatory equivalent for carbon dioxide is the ratio of ventilation to carbon dioxide produced. The increase in the ventilatory equivalent for oxygen indicates that the increase in ventilation to remove carbon dioxide is disproportionate to the body’s need to provide oxygen.
When Anaerobic Threshold is determined in this way, it seems to occur at the same time point as Lactate Threshold during incremental exercise tests. As such it may be thought of as a useful non-invasive estimate of Lactate Threshold. Furthermore, in certain populations and under certain conditions a test of Anaerobic Threshold should actually be used in favour of Lactate Threshold. For example, individuals with McArdle’s disease are unable to increase blood lactate and Hydrogen ion levels during exercise. A clear anaerobic threshold can be determined in these individuals but the measurement of Lactate Threshold is not possible as blood lactate remains at resting levels.
Ventilatory Breakpoint
With progressively increasing exercise intensity, ventilation increases in direct proportion to the rate of work being performed. That is, up until the ventilatory breakpoint, at which point there is a disproportionate increase in ventilation in an attempt to clear excess Carbon Dioxide. This is because the ventilatory threshold corresponds with the exercise intensity at which oxygen delivery to the muscles is no longer able to support the energetic demands of exercise and so more energy is derived from glycolysis. This results in the increased production of lactic acid, which is then broken down into various bi-products. One of these by-products is carbon dioxide, which stimulates chemoreceptors that signal the inspiratory center to increase ventilation.
Ventilatory breakpoint has actually been shown to be superior to Lactate Threshold in its ability to predict cycling time trial performance (Amman et al., 2006). Whether this holds true across a range of different exercise modalities is not known. However, it does suggest that it may be unwise to disregard research findings that have made use of the ventilatory breakpoint as a means of measuring the efficacy of endurance training interventions. Care should be taken, however, when evaluating the findings from different studies as conflicting findings can sometimes be attributed to differing methods of measurement.
SUMMARY - Measuring Blood Lactate
Blood lactate represents the balance between muscle lactate production and lactate clearance. There are many different measurements of blood lactate levels. Lactate threshold is the exercise intensity at which blood lactate values rise above resting levels. Lactate Turn-point is the exercise intensity at which a sudden and sustained increase in blood lactate readings is seen. Both of these variables are able to predict endurance performance with considerable accuracy.
The gold standard measurement is considered to be Maximum Lactate Steady State (MLSS), which is the highest power output at which the increase in blood lactate is less than 1.0mM/L across the last 20 minutes of a series of 30 minutes trials. While this is perhaps a more robust measurement, it is time and labour intensive, and as such rarely used. By contrast, Onset of Blood Lactate Accumulation (OBLA) is much easier to determine but is less precise in comparison with the other measures.
Additional Note
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References
- Jones, A. (2006). ‘The physiology of the world record holder for the womens marathon’. International Journal of Sports Science and Coaching, 1 (2), pp. 101-16
2. Jones, A. M., Carter, H. & Doust, J. H. (1999). ‘A disproportionate increase in VO2 coincident with lactate threshold during treadmill exercise’. Medicine and Science in Sports And Exercise, 31, pp. 1299–306
3. Jones, A. (2006). ‘The physiology of the world record holder for the womens marathon’. International Journal of Sports Science and Coaching, 1 (2), pp. 101-16
4. Pringle, J. S. M. and Jones, A. M. (2002). ‘Maximal lactate steady state, critical power and EMG during cycling’. European Journal of Applied Physiology, 88 (3), pp. 214-26
5. Smith, C. G. and Jones, A. M. (2001). ‘The relationship between critical velocity, maximal lactate steady-state velocity and lactate turnpoint velocity in runners’. European Journal of Applied Physiology, 85, pp. 19-26
6. Amman, M., Subudhi, A. W. & Foster, C. (2006). ‘Predictive validity of ventilatory and lactate thresholds for cycling time trial performance’. Scandinavian Journal of Medicine and Science in Sports, 16 (1), pp. 27-34