How many times have you looked at your power meter or heart rate monitor and wondered if you were going too far above your threshold? Although it is reasonable not to kill yourself ‘just because’ when you’re out training and racing, you might be surprised by how little you actually know about one of the most discussed – and misunderstood – performance metrics: the Anaerobic Threshold (AT) or Functional Threshold Power (FTP).

Let’s first start with answering the question: what is the anaerobic threshold? Click here if you want to skip this part and scroll down to “why you might be overthinking it”.

The anaerobic threshold

We define the anaerobic threshold as: the max intensity at which lactate combustion matches lactate production. That means that in steady state, there is no increase or decrease in lactate concentration, at this intensity.

There are other terms that try to describe the same phenomena, like maximal lactate steady state (MLSS), lactate threshold and functional threshold power (FTP). Watch the video to learn about the similarities and differences:

When AT is the max intensity at which lactate combustion matches lactate production, then wouldn’t it be interesting to look at those separately? This means we don’t only look at the result (lactate concentration) but also at the cause. Here’s how that works:

Summarized: there is a lactate production in the glycolysis and a lactate combustion in the aerobic energy system. Increase the performance of the aerobic energy system (VO2max) and you’ll increase the anaerobic threshold (left/first image). Increase the performance of the anaerobic glycolytic energy system (VLamax) and you’ll decrease the anaerobic threshold (right/second image).

How anaerobic threshold depends on VO2max - INSCYD
By increasing your VO2max, you increase your AT (all other things equal)
How anaerobic threshold depends on VLamax - INSCYD
By increasing your VLamax, you decrease your AT (all other things equal)

But (when) does the anaerobic threshold really matter in the first place? Let’s continue!

The anaerobic threshold is a blurred line

AT/FTP is conceived as the highest workout intensity at which the concentration of lactate in your blood reaches a steady state. At this intensity, the lactate stabilizes at a certain concentration and does not increase over time. Athletes are normally so afraid of passing that single power unit (or heart rate beat) they have been told is their AT/FTP, that as soon as they get close to that limit, they start to back off. But what they – and maybe you – don’t know is that AT/FTP is not a fixed value – it’s actually a blurred line.

If your AT / FTP  has been determined by a test at 300 watts, for example, what you should know is that you can increase your power output slightly above that 300 watt limit and – for example – go higher to 308 watts without blowing up just yet. The most interesting thing here, is that your body may actually find another lactate steady state where you can exercise for a pretty long period of time.

Do you prefer to watch a video instead of reading this article? Watch our webinar recording, with many extra details and training applications:

Because of the small increase, the lactate levels in your blood will initially increase too, but not so much to make you “blow up” and force you to drop the intensity. This is due to the fact that a slight accumulation of lactate can be associated with a negative feedback on the lactate production itself. A controlled accumulation of lactate can actually be associated with slowing down the lactate production itself, up to the extent where the concentration reaches another steady state and stabilizes!

“A slight accumulation of lactate can be associated with a negative feedback on the lactate production itself”

The second “steady state” is an intensity where you can stay at for quite a long time. This is possible because your AT is not a fixed value. Again, it’s a blurred line within which you can move around and over (and up to a certain extent of course).

Clearly, there is an upper limit where exercising at a specific output is not a “steady state” anymore, and if you spend too much time in that area you eventually “blow up”. And that is why it’s so important to test yourself regularly and know where the blurred line is. The same rule applies to any sport: in swimming and running, for instance, you just replace the power in watts with speed and pace and the mechanisms are the same. These are also blurred lines within which you can “play around”.

AT/FTP: most popular – least ever used

The other very important thing you maybe didn’t know about AT is that it doesn’t really come to use in any specific race or distance. If you run a 10k race for example, you will never run at AT, but your average intensity/speed would be higher (and the same will be even more true in a 5k race). Even in a half-marathon or a full-marathon, you will be hardly running at your AT speed, as you will be running below that threshold. And even when Peter Sagan is attacking on the Oude Kwaremont in the Tour of Flanders or Marcel Kittel is sprinting in the Tour de France, they’re not riding at their AT. There is almost no scenario where you actually ride at AT.

The only event where an athlete might really be at threshold for the majority of the race is a long time trial that lasts around one hour, and even in this event the athlete will be racing at AT just in part. The majority of every other competition in swimming, running, cycling, etc. are decided in situations where the athlete is well above AT! But in long-distance events like marathons and triathlons, the intensity will be well below AT/FTP for the majority of the time.

“The majority of races in swimming, running, cycling, etc. are decided in situations where the athlete is well above AT / FTP!”

So why does AT matter so much? Well, people are using it because the intensity (power or pace depending on the discipline) correlates pretty nicely with the performance in a lot of events. Statistically, if you know your threshold, you will have a pretty good idea of how you will perform in every kind of scenario. But AT is only a statistical indicator and you should bear in mind that it is possible to run significantly above or below AT intensity – possibly even more than what you’d thought.

What might surprises you the most is that the majority of the amateurs can stay above AT /FTP more easily than professional athletes. Professional endurance athletes may have a higher anaerobic threshold, but once they exceed it, the accumulation of lactate and fatigue is – in most cases – much quicker than in amateurs. Even more specifically, some pro riders can stay above it more than others: according to their specific physiology and specialization; Sagan can stay above it for a longer period of time compared to Froome for example.

Should you use the anaerobic threshold to describe training zones?

AT/FTP has been historically used to prescribe training intensities, and of course it’s not bad for this purpose. However, it is not the most efficient and precise way to prescribe training intensities and training zones. The fuel utilization, such as FatMax, below AT/FTP can be vastly different and a simple extrapolating from the AT/FTP to a lower intensity isn’t valid.

INSCYD Training Zone Builder - cycling
Here's an example of cyclists riding at the same %FTP, while experiencing very different training effects.

The same is true for high intensity efforts: the ability to ride above threshold is not directly correlated to the power at AT/FTP, and it can differ quite a lot.  For example, the only valid way to plan a VO2max interval training session is to base the intensity of an interval on the VO2max itself = the physiological system you are targeting with this specific training. Consequently, this training should be based on the specific VO2max, and not extrapolated from AT/FTP.

“The only valid way to plan a VO2max interval training session is to base the intensity of an interval on the VO2max itself”

So why should you base training intensities on anaerobic threshold or FTP, when you can also base them on the system your training to improve? Here’s how you can easily do that, using our Training Zone Builder.

Wrap up

Yes it can be important to know your anaerobic threshold, but don’t overthink it. Focus more on the actual cause/mechanism behind your AT, since that is also the only way to improve it.

Infographic: increasing FTP power with INSCYD

With INSCYD you can learn more about your lactate production and combustion rates. Simply do an INSCYD test to get the data.

To fully understand the practical application of the anaerobic threshold, we highly recommend watching our (free) webinar recording.