The Talk Test and Aerobic Threshold for Runners
There are lots of ways runners traditionally track improvements in their fitness, such as testing pace over a 5km or park-run or during repeats on the track. However, when it comes to long-distance running, these relatively short and intensive measures are not all that relevant, and improvements over these distances don’t always translate to improvements over an hour or more of running.
What matters more for many fell and trail runners; particularly those competing for 2-3 hours or more, is pace at the so-called ‘aerobic threshold’. This is a very good marker of general aerobic fitness, and particularly the ability to use fats for fuel and conserve precious muscle glycogen in order to enhance endurance.
The aerobic threshold also marks an important physiological tipping point, above which metabolic stress, catecholamine levels (hormones produced by the adrenal glands) and muscle activation increases markedly (Seiler & Kjerland, 2006). This threshold is typically used to differentiate key training intensity zones. More specifically, it demarcates the boundary between Zones 2 and 3 in a Seven-Zone system and between Zones 1 and 2 in a Three-Zone system, as described here.
Having an awareness and understanding of the aerobic threshold and a way to test this is therefore a key tool for many endurance runners, since it allows training zones to be set more accurately, and for progress to be measured in a more valid way.
In this article, we’ll take a more detailed look at what the aerobic threshold is, and how to determine where this sits using a simple protocol known as the ‘talk test’, including some audio recordings to help you understand this threshold in practice.
What is the aerobic threshold?
You may be familiar with the term ‘threshold’ or ‘lactate threshold’ in the context of running intensity, pace or heart rate. For example, you may have seen people referring to a ‘threshold run’ or a session performed at ‘threshold heart rate’.
In fact, there are two key physiological thresholds that demarcate different metabolic conditions within the body. These can be determined in different ways (such as by measuring lactate, or the amount of oxygen and carbon dioxide in expired air). These are shown in the chart below, in the context of lactate levels:
The second threshold is the one we hear the most about, and is generally what people are referring to when they describe ‘threshold pace’ or ‘threshold heart rate’. The second threshold (sometimes referred to as the ‘anaerobic threshold’ or ‘maximal lactate steady state’) is the highest intensity at which blood lactate levels remain constant (there are also slightly different ways this can be defined, but we won’t cover those here). Above this threshold, the energy demand exceeds the rate at which oxygen can be supplied and processed by the muscles, and this causes a build-up of fatiguing metabolites, which leads to fatigue much more rapidly than if the intensity is maintained just slightly below this threshold.
The first threshold, on the other hand, is spoken about much less. This is the threshold we’re focussing on in this article, and is referred to as the ‘aerobic threshold’.
Contrary to what the name might suggest, the aerobic threshold is not an intensity where you switch between aerobic or anaerobic energy systems!
As a quick physiology refresher, the body has several mechanisms through which it can produce energy. The two main ones that are used to during long-duration, aerobic exercise are the break-down of fats and carbohydrates.
The break-down of carbohydrates (also known as ‘glycolysis’) is a really efficient system that can supply energy quickly. However, the body only has sufficient carbohydrate stores (in the form of muscle and liver glycogen, and blood glucose) to fuel all-out exercise lasting roughly 90-minutes. At most race-like intensities, even if you consume carbohydrates while running, there will almost always come a point where the body’s glycogen stores are substantially depleted, and you’ll find yourself ‘bonking’ or ‘hitting the wall’. Indeed, glycogen depletion is thought to be the key cause of fatigue in endurance running (Ørtenblad et al., 2013).
In addition, glycolysis produces metabolic byproducts that are linked with fatigue. While the body is capable of using oxygen to help ‘hoover' these byproducts up to a certain extent, there is still some ‘leakage’ of these metabolic byproducts, and so broadly speaking, the more you rely on carbohydrates, the more fatigue you accrue, and the harder the effort feels.
In contrast, the break-down of fats is a preferable system for the body during lower-intensity activity, firstly because this system is very sustainable (even the leanest cyclist has ample stores of fat to fuel exercise for days!). Secondly, unlike carbohydrates, the fat oxidation system does not produce any fatiguing byproducts; just water and carbon dioxide, which the body can easily remove if in excess.
The key draw-back of fat oxidation is that it’s a slower process, so as you ramp up your pace, your metabolism is forced to shift to rely more on carbohydrate oxidation in order to supply energy quickly.
The aerobic threshold, is the intensity where you begin to need to draw on your carbohydrate stores to a notable extent (Spurway, 1992).
In effect, below your aerobic threshold, exercise is sustainable ‘indefinitely’ (in practice, this isn’t true because factors other than glycogen depletion come into play).
Above the aerobic threshold (but below the second threshold), exercise is still sustainable for several hours, but the point of fatigue will be strongly determined by muscle glycogen stores, and at some point you’ll hit a wall where exercise cannot be continued due to glycogen depletion.
Importance of the Aerobic Threshold
The aerobic threshold is important for runners because it indicates the ability to use fats for fuel, and is a very strong indicator of endurance abilities.
Having a higher aerobic threshold means that you’ll be able to sustain a higher pace for multiple hours.
Indeed, long endurance events such as trail or fell races lasting 3 or more hours, or ultras will be completed at an intensity that’s very close to the aerobic threshold, and this is arguably the main physiological variable you want to try to improve through training.
Even among races that are shorter and/or more stochastic in terms of intensity (e.g. short, hilly fell races), it can be important to have a well developed first threshold.
This is firstly because the ability to produce hard efforts after 1-2 hours of racing is a key requirement, and having a higher first threshold means that you’re better able to conserve muscle glycogen for these determinative parts of the race.
Secondly, the ability to use fats efficiently for fuel strongly impacts the location of the second threshold, because it leads to a lower rate of lactate production for a given power output. Thus spending time developing your first threshold is a necessary part of raising your second threshold.
This is often why endurance runners of all disciplines undertake a “base” training phase, where a key goal is to lift the aerobic threshold.
How to determine the aerobic threshold?
There are three key ways that you can determine the location of your aerobic threshold.
Perform a lactate ramp test. This can be performed in a lab, or if you have a lactate analyser it could also be performed at home. We have a testing protocol article here in the context of cycling. We’ll be creating a running version of this article soon, but in the meantime, just drop us an email if you need advice on adapting the protocol for running.
Visit a lab for gas analysis. This will involve running for short ~4-5-min stages while wearing a mask that will measure the amount of oxygen and carbon dioxide in the air you breathe out.
Perform a talk test. This is by far the most accessible method for most runners, and can be performed in your own time, without the need for any equipment or lab access! We’ve set out the talk test protocol below…
Talk Test Protocol
When you step over the aerobic threshold and there’s a notable increase in carbohydrate oxidation, we also see a concurrent break-point in breathing rate. This is caused by an increase in carbon dioxide production, which increases the so-called ‘ventilatory rate’.
With the talk test, we’re trying to identify this particular ventillatory break-point.
Pre-Test Requirements
You will need the following:
A Garmin watch/similar that can record time, pace and heart rate. Make sure you have your watch set up so that you can see all of these variables on one screen.
Ideally a heart rate chest or upper-arm strap. If you only have a heart rate monitor on your wrist watch, that will be less reliable but is ok if it’s all you have. In this case, you should make sure that your watch is done up tightly to minimise movement of the optical heart rate sensor on your wrist, and improve the quality of your heart rate data.
A mobile phone with an app to record your voice (e.g. Voice Memos on iPhone).
Somewhere flat that you can run continuously for roughly 20-30 minutes.
Protocol Steps
If wearing a chest strap, moisten the electrodes on your chest before beginning the test. This will help the strap pick up your heart rate correctly.
Warm up at a low intensity for around 10-mins. Take care to keep the intensity very low (subjectively no more than a 2/10 or no more than 65% of threshold heart rate). Keep an eye on your heart rate during this warm-up, so you can reposition/re-moisten your heart rate strap if the readings are looking incorrect (e.g. very high).
Press the lap button on your watch once you’re ready to begin the test.
Begin running at a slow pace that you’re confident is well below your aerobic threshold. This should feel very easy, and your breathing should be very comfortable. For some people might even be at or close to walking pace. A good rule of thumb is to start this test roughly 4 min/mile slower than your 5km pace.
Run for 4-mins holding your pace as consistent as possible.
In the last minute, say the following paragraph, filling in the gaps according to the information you see on your watch, and recording yourself on your phone as you speak, trying not to slow down while you do this(!):
“I’m doing the talk test to help me determine the top end of my Zone 2, which is also known as the ventilatory threshold or the aerobic threshold, and is an important indicator of endurance.
My heart rate is ____ beats per minute.
My pace is _____ minutes per mile (or kilometre*).
My perceived effort level is a score of ___ out of 10”
Once the 4-minutes is finished, press your lap button and repeat steps 3-6 again, but at a slightly faster pace (we’d recommend 30-seconds per mile faster for experienced runners, or 20-seconds per mile faster for less experienced runners), recording the paragraph above each time. Continue this process, increasing your pace every 4-minutes, and making sure you press your lap button at the start of each 4-minutes.
Stop the testing when your breathing makes it hard to read the sentences above, or if your effort level feels like an 8/10 or more.
* Select miles or kilometres depending on which units you prefer to use.
Try to read the paragraph in full, without shortening any sections and without taking long pauses between sentences. This will help you properly detect changes in your breathing and ability to speak. Otherwise, it’s possible to mask any changes in your breathing (e.g. by reading the paragraph quickly, and then catching up on your breathing after you’ve finished reading, or by taking deep breaths between sentences).
For guidance on what the different effort levels feel like, see table below. You can also print out our talk test print-out, which will help remind you of the paragraph above and the perceived effort levels below.
Analysis
Once you’ve finished the testing, you can listen back to your recordings one after another. You should be able to hear a marked difference in your ability to read the sentences at the transition between two subsequent stages of the test. For example, in stages 1-3, you may notice that you’re able to read the sentences without much trouble, and you’re able to take a breath at a normal point in the sentence. Your breathing may be more audible than it would be if you were at rest, but your breathing rate is similar to what it would be at rest.
When you get to stage 4, you may then notice that you’re having to speak in broken sentences, because your breathing rate has increased. You’ll notice that speaking isn’t as comfortable at this point, and that this is also true of subsequent stages (e.g. stages 5 and 6, if you went that far).
The top end of your Zone 2 should be set as the highest heart rate you achieved while your breathing rate was comfortable and ‘unbroken’. In the example above, this would be stage 3.
You can also make a note of your pace for this stage. When you test in the future, you would hope to see an improvement in the pace you can hold while your speaking remains comfortable and unbroken. This reflects an improvement in the pace you should be able to sustain over several hours.
Don’t confuse the second threshold…
It’s worth noting that we also have a second ventilatory breakpoint (i.e. change in breathing rate), which occurs at the second threshold described above. When you step over this second threshold, you’ll transition from being able to speak in broken sentences to finding it hard to speak more than one or two words at a time. Make sure you don’t confuse these two thresholds, as they are quite different!
As a rule of thumb, the aerobic threshold will sit at an effort level that feels something like a 3-5/10. If you think you’ve identified your ventilatory break-point, but it feels more like a 6-8/10 you’re probably detecting the second threshold!
At all stages of the talk test, you should be able to talk. The distinction we’re looking for is whether this talking is easy and unbroken, or a bit harder and more broken!
Talk Test Examples
Here we’ve included some example recordings so you can get a sense of what your breathing may sound like at different stages of the talk test.
In this first example, I’m well below my first ventilatory threshold. I can speak the sentences without any trouble at all:
In this second example, I’m still below my first ventilatory threshold. You may notice that my breaths are a little deeper and more audible. However, the breathing frequency is similar, and I’m still able to speak in full sentences.
In this final example, I’ve just crossed my first ventilatory threshold. You’ll notice that my breathing frequency has increased, so that I’m now having to take breaths mid-sentence. This is the key sign that the first ventilatory threshold has been crossed. If I’d tried, I probably could have spoken a full sentence very quickly without needing to take a breath. However, I’d have probably have been out of breath from having done that. As mentioned above, it’s important to try to speak the sentences at a normal rate, and just allow yourself to breathe as you would do naturally if you were chatting to someone.
Talk test print-out
Finally, to help you on your way, here’s a print-out you can download and take with you on your runs and remind you what you need to say and what the different effort levels feel like.
References
Ørtenblad, N., Westerblad, H., & Nielsen, J. (2013). Muscle glycogen stores and fatigue. The Journal of physiology, 591(18), 4405-4413.
Seiler, K. S., & Kjerland, G. Ø. (2006). Quantifying training intensity distribution in elite endurance athletes: is there evidence for an “optimal” distribution?. Scandinavian journal of medicine & science in sports, 16(1), 49-56.
Spurway, N. C. (1992). Aerobic exercise, anaerobic exercise and the lactate threshold. British Medical Bulletin, 48(3), 569-591.
