Endurance training is full of buzzwords and performance metrics. Terms like VO2 max, lactate threshold, and aerobic base often get thrown around in training plans and athlete conversations.
While VO2 max (your maximum oxygen uptake) is a well-known indicator of aerobic potential, it’s not the only number that matters when it comes to endurance performance. Another important concept for runners and other endurance athletes is the anaerobic threshold.
The anaerobic threshold marks the point during exercise when your body shifts from primarily using aerobic energy systems (which rely on oxygen) to relying more on anaerobic processes to generate energy.
This shift happens because the intensity becomes high enough that your muscles require energy faster than oxygen can be delivered. As a result, lactate begins to accumulate in the blood, and if intensity continues to rise, fatigue sets in quickly.
But what does this actually mean for your training? How do you measure or increase your anaerobic threshold? And why does it play such a big role in race performance?
I’ll break down the science behind it to show you how to train smarter and push it higher.
What Is Your Anaerobic Threshold?
The anaerobic threshold refers to the intensity of exercise at which your body shifts from being able to produce energy through primarily aerobic metabolic pathways to the need to produce more energy through anaerobic glycolysis, resulting in a significant accumulation of blood lactate, metabolic acidosis, and an increase in respiration rate to exhale excess carbon dioxide.
According to researchers, the anaerobic threshold is one of the most significant physiological variables in endurance sports. It may also be referred to as Lactate Threshold, Ventilatory Anaerobic Threshold, Onset of Blood Lactate Accumulation, Onset of Plasma Lactate Accumulation, Heart Rate Deflection Point, and Maximum Lactate Steady State.1Ghosh, A. K. (2004). Anaerobic threshold: its concept and role in endurance sport. The Malaysian Journal of Medical Sciences : MJMS, 11(1), 24–36. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3438148/
All of these essentially refer to the same point in exercise intensity or pace from a practical perspective, but are looking at slightly different physiological measures of what changes at this point.
Ultimately, when you cross the anaerobic threshold, you will experience a significant rise in blood lactate concentration due to increased lactate production, so you can generally only sustain efforts above this threshold for a short duration before significant fatigue sets in.
Typically, for most endurance sports, your anaerobic threshold is the key predictor of your performance potential because the pace that you can sustain at or just below your anaerobic threshold is the pace that you will be able to maintain for endurance races.
Pushing beyond this pace and crossing the anaerobic threshold will result in rapid and significant fatigue, causing you to “crash“ or run out of steam, with your legs burning and your body screaming to stop or slow down.
According to research, the anaerobic threshold, a concept introduced by Karlman Wasserman, is defined as the point at which blood lactate concentration sharply increases with an excess of pulmonary carbon dioxide output during a progressive exercise test.
The physiological principle underlying the anaerobic threshold is that when exercise intensity increases to a certain point, you are unable to take in and deliver enough oxygen to your working muscles at the rate at which they need it.
This relative lack of oxygen requires the muscles to increase the rate of anaerobic glycolysis. This, in turn, increases the rate of lactate and hydrogen ion production and subsequent concentration in the muscles.
The presence of hydrogen ions decreases the pH in your muscles and blood, which requires more buffering in the blood by plasma bicarbonate and carbon dioxide release.2Anaerobic Threshold – an overview | ScienceDirect Topics. (2018). Sciencedirect.com. https://www.sciencedirect.com/topics/medicine-and-dentistry/anaerobic-threshold
When carbon dioxide concentration (VCO2) increases, more must be exhaled, so you have to breathe harder and faster.
How to Measure Your Anaerobic Threshold
There are several methods for measuring your anaerobic threshold or lactate threshold, some of which are estimates, while others are more direct laboratory assessments.
#1: Steady-State Heart Rate
If you are a trained endurance athlete, one of the best ways to approximate your anaerobic threshold is to take the mean heart rate, or average heart rate, during a longer-duration race, such as a 10 km or half-marathon.
#2: Graded Exercise Test
The gold standard for measuring your anaerobic threshold (lactate threshold) is to undergo a graded exercise test in an exercise physiology lab with blood lactate measurements.
This is an invasive procedure that involves running on a treadmill at increasing intensity while blood samples are taken at different intervals. Then, the lactate concentration in your blood is plotted on a graph relative to the intensity of your exercise.
The point at which the increase in blood lactate concentration is no longer linear but instead hits a more exponential rise would be considered your lactate threshold, or for all intents and purposes, your anaerobic threshold.
Variations of this protocol, such as the Mader Test, also exist where your lactate threshold is automatically “reached“ and determined once your blood lactate levels reach four mmol/L.
#3: Conconi Test
This graded exercise test doesn’t directly measure anaerobic or lactate threshold because no blood lactate samples are taken. Of course, this makes the test far less invasive and easier to perform, but the results will be less accurate.
Rather than relying on actual blood lactate concentration data, the Conconi Test measures your heart rate at different intervals as the exercise intensity increases.
The “anaerobic threshold“ is determined by plotting your heart rate versus workload on a graph and identifying the deflection point where the trend shifts from a linear relationship to one with a more pronounced slope.
#4: Estimation Formula
A very rough estimate of your anaerobic threshold can be made by taking 85-90% of your maximum heart rate.
Theoretically, this method is effective because the anaerobic threshold typically corresponds to this heart rate range for most trained individuals.
However, the accuracy of this method will largely depend on how accurately you determine your maximum heart rate.
If you have a true maximum heart rate measurement from a maximum heart rate field test, this will yield a reasonably accurate anaerobic threshold estimate.
However, using maximum heart rate estimation methods, such as the 220-age formula, will inherently be less accurate, as there’s a significant standard deviation or margin of error associated with these formulas.
What Is the Difference Between Anaerobic Threshold and Lactate Threshold?
Anaerobic threshold and lactate threshold are often used interchangeably and occur at about the same level of intensity, and they both represent the maximum pace that you can sustain for an extended duration before significant fatigue sets in.
The primary difference between anaerobic threshold and lactate threshold lies in the way they are measured.
Lactate threshold specifically looks at blood lactate concentrations during graded exercise, whereas anaerobic threshold looks at changes in oxygen consumption and carbon dioxide exhalation.
Most sports scientists and exercise physiologists take the lactate threshold to be the point at which blood lactate concentrations exceed four mmol/L.
What Is the Difference Between Anaerobic Threshold and VO2max?
VO2max (short for maximal oxygen uptake) refers to the maximum amount of oxygen your body can take in during exercise. It is measured in millilitres per kilogram per minute.
The anaerobic threshold is commonly expressed as a percentage of VO2 max.
In non-athletes, the anaerobic threshold is generally about 50-60% of VO2max. In athletes, the anaerobic threshold is 75% of VO2max or above.3Pennington, C. G. (2015). The Exercise Effect On The Anaerobic Threshold In Response To Graded Exercise.docx. Pennington, C. G. (2015). The Exercise Effect on the Anaerobic Threshold in Response to Graded Exercise. International Journal of Health Sciences, 3(1), 225-234. https://www.academia.edu/35153450/The_Exercise_Effect_On_The_Anaerobic_Threshold_In_Response_To_Graded_Exercise_docx
This is because athletes have better cardiovascular fitness, and their aerobic systems have undergone more adaptations to facilitate increased oxygen uptake.
Anaerobic respiration and VO2max are correlated in the sense that the higher your intensity of exercise and the greater your level of anaerobic respiration, the closer your oxygen consumption is to your VO2max.
How to Improve Your Anaerobic Threshold
There are basically two arms that need to be addressed to help increase your anaerobic threshold.
Essentially, you need to reduce the production of lactate—directly increasing your anaerobic threshold—and improve your body’s rate of removing and using lactate and buffering the acid (hydrogen ions), which is brought on by improving your anaerobic fitness and efficiency.
When addressing the first arm, the rate at which lactate is produced, you need to improve your aerobic efficiency such that you can take in, deliver, and utilize oxygen more efficiently and at a faster rate during higher-intensity exercise.
Essentially, this involves increasing your VO2 max or aerobic capacity.
If you can better meet the oxygen demands of your muscles at a faster pace, you will be able to continue supplying ATP, or cellular energy, through aerobic metabolic pathways rather than needing to switch over to anaerobic glycolysis, which in turn produces the hydrogen byproducts that ultimately cause fatigue.
When training to improve your anaerobic threshold, focus approximately 85-90% of your training efforts on enhancing your aerobic capacity and about 10-15% on anaerobic-specific workouts.
The anaerobic workouts should be intense and involve repeats of the same length (rather than a ladder or pyramid) with full rest in between.
These workouts should focus on increasing your anaerobic endurance over time, but increasing the duration during which you can exercise at maximum capacity.
To ensure that you are targeting only the anaerobic system, rather than playing around in the murky middle or “gray zone,” these intervals should be super intense, fast, and short in speed.
For example, a great workout to improve anaerobic endurance is to find a short, steep hill. After a warm-up, sprint at maximum effort up the hill for 10 seconds. Mark where you end on the hill at the end of the interval.
Take a full recovery and then go again.
Continue your repeats with full recovery until you can no longer reach your finish mark in the 10 seconds. This signals that your endurance training workout is over.
Once you do a workout where you can hit 10 reps at your distance, you are ready to progress to the next workout.
In the next session, increase the sprint time to 12 seconds while maintaining the same high intensity.
Again, once you can complete all 10 reps at maximum effort and reach your 12-second maximum mark, you can increase the following workout to 14 seconds.
Space these workouts at least one week apart.
Many coaches suggest that performing longer submaximal intervals, teetering just at or above your anaerobic threshold pace, is the best way to improve your muscles’ ability to remove lactate and buffer acid, allowing you to continue exercising at a high workload.
For these types of anaerobic threshold workouts, the rest period should be approximately as long as the interval itself for beginners and around 75% of the interval for advanced athletes.
Here are some examples:
- 6 x 800 meters with 3 minutes rest
- 4 x 1000 meters with 3 minutes rest
- 4 x 1200 meters with 4 minutes rest
- 5 x 4 minutes with 3 minutes rest (4 minutes for beginners)
- 4–5 x 5 minutes with 4 minutes rest
Anaerobic threshold training should be incorporated into your weekly training (typically once a week), but don’t neglect the importance of building your aerobic base as well.
To read up on improving your aerobic base, check out our guide Run Slow To Run Fast:
FAQs
Is HIIT Aerobic or Anaerobic?
High-intensity interval training is a combination of aerobic and anaerobic metabolism, with high-intensity intervals being anaerobic and low-intensity periods being aerobic.
What is the Difference Between Lactate and Lactic Acid?
In terms of chemistry, lactic acid has an extra hydrogen atom bound to it.
Immediately after lactic acid is produced in your muscles through anaerobic respiration, the hydrogen atom and the rest of the molecule split, creating lactate, the substance that accumulates in your blood.
Whilst you may have heard people say that lactic acid accumulates in the blood with increased anaerobic energy production, this is technically incorrect, as it is actually lactate that accumulates. However, the two terms are often used interchangeably.
