Introducing auto-calculated Critical Power: Accelerate your improvements by running in the perfect power zone.

Introducing auto-calculated Critical Power: Accelerate your improvements by running in the perfect power zone.

What is new?

Today, we are introducing a new feature that will bring near-clairvoyant predictions and coach-like precision to your daily training recommendations: auto-calculated Critical Power.

Why is auto-calculated Critical Power important?

Auto-calculated Critical Power accelerates your improvements by setting the perfect power zones to train in.


Manual testing takes a snapshot of your fitness at a single point in time. Even though your fitness capabilities were constantly changing, your training zones would remain static until you completed another test.

Now, auto-calculated Critical Power will adapt your power zones to your changing fitness.

What are the new features in the Stryd ecosystem?

  • Stryd's ecosystem will now auto-calculate your Critical Power from your recent training data.
  • Android, iOS, and PowerCenter will show your most up-to-date Critical Power and power zones after every run.

What are the benefits?

Here is a list of benefits you can immediately expect to see from this new tool.

1. Your power zones are always accurate and up-to-date.

Always up-to-date power zones will allow you to gain maximal adapations from your training.

2. You will have a realistic understanding of your current fitness heading into race day.

The Stryd mobile app will tell you the correct power target for race day so you can run with the confidence that you are leaving it all out on the course.

3. The manual Critical Power test is no longer necessary.

Your training routine just became more convienent. You no longer have to find time for a difficult and training-disrupting manual Critical Power test. As long as your training plan prescribes you a wide variety of workouts, auto-calculated Critical Power will be sufficient to determine your power zones.

4. You will have a complete idea of your overall running training load due to more accurate Running Stress Scores (RSS).

How well does auto-calculated Critical Power work?

We took a three-pronged approach to test the auto-calculated Critical Power tool. We tested our new toolset against a set of competitive marathoner data from the 2019 Boston Marathon, a widespread user study, and some elite runner data.

Boston 2019


Figure 1. Manually set Critical Power vs marathon power at the 2019 Boston Marathon


Figure 2. Auto-calculated Critical Power vs marathon power at the 2019 Boston Marathon

We analyzed every Stryd data set from the 2019 Boston Marathon. We compared the average power from each race result against the Stryder’s manually-set Critical Power and their auto-calculated Critical Power. The average marathon power ended up being 86.7% of manually-set Critical Power and 88.6% of auto-calculated Critical Power. We generally recommend that marathon distance races are executed at 89-91% of Critical Power. This result means that auto-calculated Critical Power did a better job of predicting marathon performance compared to the manual method.

Additionally, the auto-calculated Critical Power target gave more realistic expectations of race performance for more people. It prescribed fewer "outlier" targets compared to manually-set Critical Power.

Beta Testing

We conducted a beta test of 150 Stryders on the new auto-calculated Critical Power feature and we received positive feedback from the real-world testing. Here are some select success stories from the beta testing phase:

  • “Stryd calculated my Critical Power to 343 watts. This is where Xert (343 watts) and WKO4 (345 watts) has me, so it is looking pretty dialed in now.”
  • “Last weekend, I ran 15 kilometers at 272 watts. Stryd calculated my Critical Power to 277 watts. Stryd did a good job of predicting my race performance.”

Elite Athlete Testing

We tested this feature on a select number of elite athletes to ensure that auto-calculated Critical Power worked at the highest level of the sport. The results were great here too. In all the cases we analyzed, Stryd accurately predicted performance for elite athletes within 1%.

How can I ensure that my auto-calculated Critical Power is accurate?

It is important to train at a variety of intensities and durations so Stryd can accurately predict your Critical Power .

Specifically, you should do three types of runs on a regular basis:

  • Short distance running such as sprinting or fast strides (10-30 seconds in duration)
  • Middle distance running such as a 10-20 minute fast tempo run or runs at 5k/10k intensity
  • Long, slow running (50+ minutes of duration)

Additionally, a short run in the 3-5 minute duration can be helpful in building your Power Duration Curve and ensuring an accurate Critical Power.

You should strive to do one run of each type on a regular basis as it fits into your training plan. Your Critical Power will be more reflective of your capabilities if you have recently done a run of each type.

How to enable auto-calculated Critical Power

You can enable auto calculated Critical Power on your Android or iOS phone.


Please download the latest version of the Stryd app from the Google Play Store before enabling auto-calculated Critical Power.


Please download the latest version of the Stryd app from the App Store before enabling auto-calculated Critical Power.

After you have enabled auto-calculated Critical Power on the phone, you can also view it on the PowerCenter.


How much data do I need for Stryd to auto-calculate my Critical Power?

In the last 3 months, you must have at least 12 runs in the PowerCenter and at least one of these runs must be longer than 50 minutes. This amount of data will give Stryd enough information to calculate an auto-calculated Critical Power for you.

How often will Stryd auto-calculate my Critical Power?

Your Critical Power will recalculate whenever you upload a new run. After the auto-calculation process is finished, you will receive a notification on your phone about the change in your Critical Power, if your Critical Power changes.

How will I know that my Critical Power has been updated?

The Stryd mobile app will send you a push notification whenever your Critical Power has been updated.

If you would like to check the last update to your Critical Power, you can open up the Critical Power menu in the Stryd mobile app and you will find the time and date of when your Critical Power was last updated.

How can I improve my auto-calculated Critical Power?

The best way to improve your Critical Power is to improve your fitness by consistently following a training plan.

You will see your auto-calculated Critical Power improve after completing high quality runs. Stryd will learn more about your current capabilities after you import these activities into the PowerCenter and adjust your Critical Power accordingly.

What does the algorithm behind auto-calculated Critical Power look like?

Stryd predicts the power you can hold at your fatigue threshold to determine your Critical Power. Stryd makes this prediction by looking at your recent training data and the maximum power you can hold at different durations. In order for Stryd to effectively determine your Critical Power, it is crucial that you do a wide variety of training including short distance, medium distance, and long distance running.

How does a race affect my auto-calculated Critical Power?

Since races are typically done at your best effort, a race is more likely to reflect your fitness than a typical training run.

Is a higher Critical Power better? Is it bad if my Critical Power went down when I switched on auto-calculated Critical Power?

With a more accurate Critical Power, you can make better training decisions and realistic race plans.

Can I try out auto-calculated Critical Power and revert back to manually-setting Critical Power if I would like?

If you would like to switch back to manually-setting Critical Power, you only need to toggle "auto-calculate" off inside of the Stryd app and you will be able to manually-set your Critical Power again.


“For me, running is both exercise and a metaphor. Running day after day, piling up the races, bit by bit I raise the bar, and by clearing each level I elevate myself.” - Haruki Murakami

Critical Power is the key to precision in training and max performance on race day. With the introduction of auto-calculated Critical Power, you can now run with the perfect power target during every training run and race. This new innovation will allow you to accelerate your training progress because you will always be running to your potential.

If you are a current Stryder, please update your Stryd mobile app and then open up your app to enable auto-calculated Critical Power. If you are not yet a Stryder, please click here if you would like to learn about and purchase the new Stryd.

The Stryd Team