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 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-CP is only as good as the data it receives from your training. The variety of your running is important in accurately calculating your CP. Learn about generating an accurate CP in the next section.
Note your CP 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 CP. We provide this option within the app. See instructions here.
How do I make sure my CP is accurate?
The more variety you have in your running, the more accurate your Critical Power will be. We recommend the following:
Long runs over an hour in duration.
Medium distance runs of 10-20 minutes at race intensity.
Short distance sprints or strides at max effort (10-30 seconds in duration).
Stryd will use approximately 90 days worth of runs to determine your CP. The runs that contribute to your Critical Power can be viewed in the Power Duration Curve.
Note if your first three runs with Stryd don't have the variety as defined above, then your CP is going to be off. E.g. if you go for three easy runs when you first buy Stryd and you get a CP, it is likely to be underestimated. Make sure to add the above variety before using the defined Stryd Power Zones as a guide.
Advanced users manually calculating their CP can do Critical Power tests every two-three months and then enter the results in the app. See the testing protocol here.
So I have a CP, now what?
Awesome, you now have a snapshot of your current fitness! Your Critical Power determines your Power Zones which are a power range or ‘zone’ for executing different types of runs. Every run will be executed at a different % of your Critical Power. As you push yourself Stryd will see your improvement and adjust your CP and corresponding zones accordingly.
Your CP 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 boundary of the zone. You should find an effort that feels easy and the number that works for you.
I had a great run, and improved my PDC but my CP went down... why?
Your CP 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 CP 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.
Steve Palladino, a power-based coach has a great article on how Stryd auto-generates a CP based on your running activity. If you want more insight into how your runs affect your CP, read his article here.