Critical Power Definition

What is CP? What is Critical Power?

Updated over a week ago

The definition of Critical Power

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.

How do I use Critical Power?

Your Critical Power is an estimate of your maximum metabolic effort for about 40 minutes. Critical Power by itself can be confusing, 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.

How do I get my Critical Power?

After purchasing Stryd, simply go for a few runs with it. Your Critical Power (CP) will automatically generate after a few runs and continue to update as it gets to know you and your fitness improves. This is your first step in moving from traditional training to power-based training.

But, your auto-calculated Critical Power is only as good as the data it receives from your training. The variety of your running is important in accurately calculating your Critical Power. Learn about generating an accurate Critical Power in the next section.

Note your Critical Power will change often at first as you do more runs and Stryd gets to know you but will slow down over time with more incremental changes less frequently.

Advanced users may want to manually calculate their Critical Power. We provide this option within the app. See instructions here.

How do I make sure my Critical Power is accurate?

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:

  1. Long duration runs of 40-60 minutes at max effort or near max effort (time trial or 10k race) for those that are training for a half or full marathon distance.

  2. Medium duration runs of 10-20 minutes at max effort or near max effort (time trial or 5k race)

  3. A short max effort run that is 3-5 minutes in duration.

  4. Short distance sprints or strides at max effort (10-30 seconds in duration).

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-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.


I had a great run, and improved my Power Duration Curve but my Critical Power went down... why?

Your Critical Power is determined from 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.

More information...

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.

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