How to Test for CP (Critical Power) As a Cyclists

If you’ve been a part of the cycling world for a little bit, you’ve likely heard the term critical power. As a cyclist, understanding what critical power or CP means and how you can use it is an effective tool to boost your performance and improve your gains.

What is critical power in cycling?

Critical power in cycling is the highest average power you can sustain for about an hour. It’s measured in watts.¹ Cyclists use critical power to determine their strengths, uncover weaknesses, and set zones for training. Like FTP, a higher cycling critical power likely means you can maintain a higher power during endurance cycling.

CP testing stems from the principle that your power output above a specific “critical power” follows a power-duration curve, defined by your CP and W’ (pronounced W prime).²

W’ is simply the amount of work you can expend above your CP before you tap out and are exhausted. It’s measured in kJ (units of energy). In short, W’ just shows you your ability to ride above your CP.²

What is the difference between critical power and FTP for cyclists?

Another common metric cyclists use to measure their performance is Functional Threshold Power or FTP. Your FTP is the highest average power you can sustain for about an hour without fatiguing, expressed in watts per kilogram.

Many cyclists rely on FTP to glean details about their overall fitness. It also helps cyclists gauge how difficult a ride is based on how hard they worked while cycling (aka their FTP).

FTP and critical power cycling are both popular cycling performance metrics. Sometimes, people use the terms interchangeably, but they shouldn’t. Although FTP and CP are similar measurements, they’re not the same.

FTP is the actual power you can sustain for a maximum of one hour, while critical power cycling indicates the size of your aerobic system, which is one of your body’s three energy systems. The aerobic system releases energy by burning carbs and fats with oxygen. It’s a slow energy system compared to the anaerobic system, which releases energy quicker but can be maintained for a long time (as long as your body has fuel). This is how your body produces energy to sustain you through very long bike rides.

You can determine your FTP using a short, 20-minute test, but FTP testing does have limitations. For example, it can lack accuracy if you use a shorter test to determine your FTP, and it may not be as relevant to certain types of cycling.

Alternatively, the critical power test can fill in some of those gaps and give you a more well-rounded picture of your physical abilities as a cyclist. 

What are the benefits of critical power testing for cyclists?

Critical power testing has many benefits for cyclists:³

• Critical power testing offers a more comprehensive picture of your physiology. With critical power cycling testing, you’ll get data on your maximum sustainable power and your capacity beyond this power.
• Critical power may be more factually sound. Unlike FTP testing, critical power cycling doesn’t rely on as many assumptions about physiology and how energy is generated while testing.
• It can help you zero in on key strengths. Since it offers a fuller picture of your physical abilities, critical power cycling tends to be more widely accepted across different types of cycling disciplines. As a result, you’ll be better able to glean insight into your key strengths and areas of improvement.
• It can help you pace your race or training efforts. Once you know your critical power cycling and W’, you can estimate your power over a specific duration of time. You may want to use an online CP calculator to estimate the power you can hold for a given period (or how long you can maintain a specific power) to pace your efforts.

Are there any disadvantages to CP (Critical Power) in cycling?

Like FTP, CP testing also has its limitations: 

• Time-consuming: Since critical power cycling testing requires two maximal efforts, completing the process can take a decent amount of time.
• Your performance is affected by other factors: As is true with most tests, your results will vary depending on many different factors, including hydration, fatigue, and what you ate that day.
• Can’t tell you everything: Much like FTP testing, a critical power cycling test won’t tell you everything you want to know about your physiological abilities. You need a lab for that! Unfortunately, most cyclists just don’t have access to a lab.

How to test for critical power cycling

There are a few different critical power cycling testing methods, but the two-test method is reliable and one of the simplest. Here’s how it works:

• Warm up for 10 to 15 minutes.
• Ride as hard as you can for 3 minutes. Maintain your maximum power for the test’s entire duration and ensure it’s as consistent as possible.
• Cool down.
• Take at least 30 to 40 minutes to rest or wait until the following day to complete the second timed test.
• Once you’re ready to begin the second test, warm up for 10 to 15 minutes.
• Ride as hard as you can for 12 minutes. Again, maintain your maximum power for all 12 minutes but be consistent.
• Cool down.

Once you complete both tests, get a calculator and calculate your critical power cycling this way:

1. Multiply the average power you maintained during the 12-minute test by 12.
2. Multiply the average power you maintained during the 3-minute test by 3.
3. Subtract the number you calculated in step 2 from the number you calculated in step 1.
4. Divide the resulting number by 9. This is your CP.

Alternatively, you can also use an online tool to calculate it. (If you’re not a fan of math, the latter might be the better option for you.)

What to do with your critical power results?

One of the best ways to use your critical power cycling test results is to monitor your progress. If you aim to become a better and stronger cyclist, re-test your critical power cycling every three months to see how your fitness has changed. This process can also provide valuable insight into whether your current training program is providing the results you want.

You can also use critical power to estimate your training zones, much like you would use your FTP. We recommend working with a trainer who can help you calculate your training zones and ensure they’re well-suited to your goals and manageable.

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Sources:

1. Jones, A. M., & Vanhatalo, A. (2017). The ‘Critical Power’ Concept: Applications to Sports Performance with a Focus on Intermittent High-Intensity Exercise. Sports Medicine, 47(S1), 65–78. https://doi.org/10.1007/s40279-017-0688-0 
2. POOLE, D. C., BURNLEY, M., VANHATALO, A., ROSSITER, H. B., & JONES, A. M. (2016). Critical Power. Medicine & Science in Sports & Exercise, 48(11), 2320–2334. https://doi.org/10.1249/mss.0000000000000939 
3. The “Critical Power” Concept and High-Intensity Exercise Performance. (2018, July). Gatorade Sports Science Institute. https://www.gssiweb.org/sports-science-exchange/article/the-critical-power-concept-and-high-intensity-exercise-performance