Critical Power up: that creates expectations!

Our John is training for the Rotterdam Marathon on April 16 with a schedule from Klaas and a Stryd power meter. He was one of the runners who participated in our first Critical Power Opkrik Day. With result!

When I get out of the car at ProRun in Amsterdam, I am quite early. There is a strong wind. That doesn’t bode well. Before we start boosting our Critical Power with a whole group of Stryders, I talk to Klaas Boomsma. I am very curious about the how and why of this day, with that special name. Because what is that, boosting your Critical Power? And what’s the use of that? And that wind, does that indeed not bode well?

It’s a number

Your Critical Power is a number that indicates the maximum power at which you can run approximately 10 km. This maximum endurance performance is different for each person. You can compare it with your VO2max or your FTP (Functional Threshold Power). Without going into details here, it’s about determining a number, or your threshold value.

At Stryd, this Critical Power can be determined in various ways. For example, by doing a targeted test. Stryd can also estimate your Critical Power based on a number of runs. This estimate becomes more and more accurate as you run more and more with the Stryd power meter. But… there is also a thing. And that thing is that measurements are always taken over a certain period.

Every 90 days

After 90 days, the values ​​of training sessions that determined your Critical Power until then expire. Suppose you train for a marathon and especially do a lot of slow endurance runs, it can just happen that your Critical Power suddenly drops a lot one day. That happened to me, coincidentally, a few weeks before the Critical Power Jack Up Day was announced. At first I thought it was my new Stryd, but during the jacking day it became clear to me where that lowering suddenly came from.

The impact of lower Critical Power

What difference does such a reduction in Critical Power make, you may think. This reduction has an impact if you use a training schedule that you run on wattage via the Stryd app. The values ​​of the training sessions are determined on the basis of percentages in relation to your Critical Power. After all, this is your ‘threshold’ or tipping point. In other words: Your Critical Power is the 100% value for determining your training zones.

Why is correct Critical Power so important?

That beautiful number determines the power at which you train within the different zones. If you are training for a specific distance and a related performance, you want to train as optimally as possible. Especially if you train using a schedule, those values ​​must be as accurate as possible and preferably update automatically when your performance changes. This allows you to optimally adjust the training and set realistic goals.

Race calculation

Stryd’s strength is that its power can be used for race calculations. This allows Stryd to give you a prediction about the end time of a race in advance. This goes a long way. Parameters such as altitude, humidity, temperature and GPS can be used for the calculation. You can do such a race calculation in the Stryd Power Center. In the most recent update of the Stryd App you can get these global predictions for the common distances.

Surfing the lactate wave

When I first saw such a forecast, it seemed impossible to run that pace continuously. In this article you can read how I did that. Klaas actually has the same experience. He describes it very nicely as: You continuously run at a certain capacity. You actually surf the lactate wave, so to speak, the art is not to fall off. During the race, this is quite a special experience. That apparently simple number ensures that I can run relatively fast without becoming sour.

What Klaas particularly notices about the Stryd, both for himself and for other runners, is that the Stryd is challenging and motivating. He has done several tests to determine the tipping point for his heart rate and has run several marathons with it. “If I had kept running purely on heart rate, I would never have passed the Sub-3,” says Klaas.


Klaas ran with the Stryd power meter during the Berlin Marathon. In advance the race prediction seemed on the high side. Nevertheless, Klaas decided to run on this ability, if only to see if it was correct. That turned out to work out well. Stryd predicted 2:53:02, he ended up running 2:53:17!

As long as your Stryd is right

Back to the Critical Power Jacking Day. The participants are now trickling in. First, a check is done to see if the Stryd is properly attached to the shoe. Several generations of Stryd are represented. The Next Gen and the Wind are the most common today. Klaas explains that we will first do a warm-up, by walking about 2.5 kilometers towards the Bosbaan.

Back and forth

The route turns out to be simple. 2.5 kilometers there and then back. How hard can that be now? Well… that turns out to be a nice float. The wind is, let’s say: quite present. We will also see this later in the data. I notice this myself when I just experience a floating moment and for my feeling, hanging still in the air. All participants go hard, each at their own pace. Some groups form and some hide behind a back to stay out of the wind. I keep walking in the wind myself. On my Stryd I have programmed 5 blocks that are well above my Critical Power of 319 Watt. With this I hope to be able to boost my Critical Power for a while.


A few days ago, I happened to have a fast 5K workout on my marathon schedule. Apparently Klaas had done this deliberately to boost my Critical Power. That also had the desired effect. My Critical Power went from 309 Watts to 319 Watts. After the training, the reward came through an App notification from Stryd. ‘Your Critical Power has been updated’. When I texted this to Klaas, he thought it would be a nice job for me to do this again that Sunday.

The wind gift

After about two kilometers, I see the first runners turn back. How fast are those guests! Mark stands at the turning point and shouts that it is going very well. At that moment I realize that I also have to go back. It seems like an almost impossible task. But… Stryd says it can be done, so it should be possible, right? The first 2.5 kilometers I only ran well above the set power of the three blocks. Can I still keep that up? That turns out to be true. I catch up with a few participants in front of me and I even feel able to accelerate considerably. The last, last piece. Really and truly. I promise myself and it is even confirmed by Richard, one of the participants I can now join. Only 1 kilometer left, he shouts. At that moment it gets very heavy, but I can still keep up. I cross the invisible finish line quite exhausted. It’s taking me a while to get to it. As I grab my phone, I see a message from Stryd. “Your Critical Power has been updated,” it says. I show it to Klaas and I open the message. My Critical Power appears to have increased to 333 Watt! A huge improvement. I’m sure the strong wind here has made a big contribution. Because of that enormous back pressure, you simply need more power to move forward.

In fact, everyone has a similar story to tell after their return. So it turns out to be a very good method to get the Critical Power up to date again. This day is definitely worth repeating.

What does this mean for me in practice?

My goal is to be able to run the marathon under three hours. Stryd is an important tool for me to achieve this goal. Klaas writes the schedule for me, which is based on the Stryd Wattages and my Critical Power. I set up the blocks in my digital training schedule via the Training Peaks platform, which then synchronizes fully automatically with my Stryd app. Now that my Critical Power has had a big boost, I immediately notice it in my Stryd workouts. The different zones have been adjusted and automatically the training sessions that I can perform. All in all, it is seriously going a lot faster and that gives me confidence in achieving my goal. The global race calculation currently reads 3:13:24. This was 3:26:14 a few months ago. These are calculations that do not take the aforementioned parameters into account.

Realistic predictions?

How realistic the forecast will be, I will see in the coming weeks. Of course I’m not fixated on these numbers. You have to work really hard to even get close. Although… If Stryd says it can be done, it must be possible. The marathon, on the other hand, remains a difficult distance. Everything has to be right that day. The schedule, the training kilometers and my own discipline will certainly not lie down!

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