Critical Power is the threshold at which the dominant type of fatigue your body experiences changes. This number is used to determine your optimal training intensities (Power Zones) which trigger specific fitness gains and guide your race day effort.
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Your Critical Power is an estimate of your maximum metabolic effort for about 40 minutes. Critical Power by itself can seem advanced, but when you use your Critical Power to help you estimate different training efforts, it becomes your most valuable training tool!

Notice the above graph. This is a representation of the three main metabolic training targets. With an accurate Critical Power, you will be able to hone in on improving these areas of fitness.

The Stryd team has broken this metabolic graph into 5 training Power Zones. Each Power Zone has a percent Critical Power associated with it. Using these Power Zones to train will help you improve aspects of your metabolic capacity.

Above are the 5 Power Zones that an accurate Critical Power will provide. If you have more questions about the Power Zones, please see this article: Power Zones explained

Every run will be executed at a different % of your Critical Power. As you push yourself, Stryd will see your improvements and adjust your Critical Power and corresponding Power Zones accordingly. This makes for effortless training adjustments that can account for fitness improvements or fitness losses.

Whether you are new to Stryd or an existing user, it's never too late to get an accurate Critical Power!

Before you start testing or following any specific Stryd plan, please double-check that the weight and height settings are correct on your pod.

(Accurate, Easy)

This method is the best for people who don’t know what their Critical Power should be or have not raced in the last two weeks.

The Estimated Critical Power will be calculated with a single easy run. The Single Run CP Estimation is a short 17-minute easy run with two 60-second surges.

If you feel like your existing CP is inaccurate, or if you are new to Stryd and do not have a Critical Power, you can reset your Critical Power and choose the Single Run CP Estimation as your reset of choice.

Once you complete the Single Run CP Estimation, you will want to either begin a Stryd Training plan or complete one of the Testing Workout Sets. You can find more details on this process in the Estimated Critical Power support article.

(Somewhat Accurate, Difficult)

Users can do a variety of workouts over a longer time to accurately calculate their Critical Power. Please note that these workouts must include

It will take up to five runs total for the Stryd system to calculate a Critical Power. If you do not complete maximum effort tests every 90 days, your Critical Power will become less accurate. You can either begin a Stryd Training plan or complete one of the Testing Workout Sets.

(Data Dependent, More difficult)

Users can manually enter a Critical Power value instead of relying on the Stryd system to make these calculations. User error can sometimes make this method less accurate than method 1 or method 2.

NOTE: Manually entering your Critical Power should be done cautiously. Threshold values from other running or biking power meters will not accurately reflect your ability when running with Stryd. (Power values from wrist-based power provided by your watch will not be accurate.) Also, these tests or races need to be very recent to be accurate. If you have not completed or executed one of these tests in the last 30 days, this number may be inaccurate.

To enter a Manually Calculated Critical Power you will need to have completed a 5k best effort, 10k best effort, 6-3 laps test, 9-3 minutes test, or know what your Manual entry should be. Please note that if you use a race or test to estimate your Critical Power, the race or test should be completed within the last 30 days to be considered an accurate data point.

Instructions:

The more variety you have in your running, the more accurate your Critical Power will be. Also, the more robust your metabolic capacity will be. We recommend the following:

Each of these maximum-effort training runs will help the system better understand your current fitness and metabolic capacity.

Stryd will use approximately 90 days' worth of runs to determine your Critical Power. The runs that contribute to your Critical Power can be viewed in the Power Duration Curve.

Note: Make sure to add the above variety before using the defined Stryd Power Zones as a guide.

Advanced users manually calculating their Critical Power can do Critical Power tests every two to three months and then enter the results in the app.

Your Critical Power is 245 Watts.

Your Zone 1 shows as 159 - 196 W.

You should execute your easy run between 159 - 196 W.

The range represents and upper and lower boundaries of the zone. You should find an effort that feels easy and the number that works for you.

Other Power Zones associated with this Critical Power can be found in the screenshot below. Please note that these Power Zones will only be for this individual with a Critical Power of 245 Watts.

To compare runners, we can normalize critical power by dividing CP by weight. If CP is 200 watts and weight is 50 kg, normalized CP is 4 Watts/kg. Achievable CP depends on several factors, including age. Below is a table* for comparison for people in their prime (about 30 years):

* From the Secret of Running by Hans van Dijk and Ron van Megen, page 121

Your Critical Power is determined by three major energy sources while running: immediate energy, oxidative energy and nonoxidative energy A change to one of these areas can tell the model that another is overestimated, and your Critical Power will correct itself, becoming more accurate. Continuing to do best efforts at varying durations (as described above) will push your entire curve up, and result in an improved critical power.

When your Critical Power changes, you can get a notification on your phone. This must be enabled in your notifications within the Stryd app on your phone:

The notifications work only when the automatically calculated Critical Power goes up after a hard run that forces a readjustment of your CP.

You will not get notified if:

To set a manual Critical Power, you need to have a Stryd pod that has been connected to your account and that you have disabled Auto-Calculated Critical Power.
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Once you've successfully paired a Stryd pod to your Stryd account, then you will be able to set a Manual CP by going to Settings->Critical Power->Selecting Recalculate
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If you receive a server error when trying to re-enable Auto-Calculated Critical Power it's because you do not have a Stryd pod that has been connected to your account and will be unable to re-enable until you've paired your Stryd pod to that account.

If you recently performed a CP test and would like to use this data to manually calculate your CP in the Stryd ecosystem, please follow these steps:

Now the Stryd ecosystem will use this as your CP and calculate your power zones accordingly.

If you feel like the results of this test do not fully represent your current fitness. You may want to read this article written by coach Steve Palladino: A method to roughly estimate FTP/CP for runners not ready to properly test

The least impactful way to measure critical power is to do the 6/3 lap test or 9/3-minute test on the road. Stryd uses the power and pace for each segment to estimate critical power.

Since we extrapolate CP from the 2 test segments, the power ratio between the short and long segments of the test is important. It is possible to repeat the critical power test and run at higher power in each segment, yet get a lower critical power number. If that happens, the power ratio likely change.

Possible causes:

1. In the first test, the short section was not an all-out effort, causing CP to be overestimated.

2. In the second test, the long section was not an all-out effort, causing CP to be underestimated.

3. Your training was focused more on short distances, improving your speed but not your endurance.

You can always repeat the critical power test, and with each test, you will get more proficient and closer to the best possible CP estimation. If you have done a 10k race at full effort, it is the best way to estimate CP, but it has a high impact.

Steve Palladino, a power-based coach has a great article on how Stryd auto-calculates a Critical Power based on your running activity. If you want more insight into how your runs affect your Critical Power, read his article here.