The Critical Power Chart

by

What is Critical Power?

Critical Power, or maximum mean power (MMP), is the best average power (measured in watt) you can produce on a bike in a given time frame. A Critical Power for five minutes (denoted as CP5) of 300 watt means that you can drive for five minutes with 300 watt, before you are exhausted. Other common Critical Power values are those for 20 (CP20) and 60 (CP60) minutes. You can estimate your FTP from your CP20, and your CP60 is the same as your FTP.

A Critical Power chart shows the development of the Critical Power values, from a single second to multiple hours, if you rode your bike that long. This chart is ideal to evaluate your personal performance and your strengths and weaknesses, especially compared to other athletes. If you are a sprinter, you will have higher Critical Power values below the one minute mark than other cyclists. As time trial specialist, you will have the advantage between CP20 and CP60 and as climber between CP1 and CP20.

The CP Chart is a great base for your training. Let’s assume you compete over sprint distances and have a bike split of 40 minutes. Then you should concentrate on improving your CP40, but beware, on the day of your competition you need to stay below your CP40, because you need some reserves for running.

The Critical Power chart is useful to plan the training of cyclists and triathletes, but how do you know your specific CP values? One possibility is performing the following test:

  • 20 minutes easy warm up
  • 15 seconds all-out, to determine the anaerobic power
  • 5 minutes easy. Spin your legs
  • 4 Minuten all-out, to determine your VO2max power
  • 10 minutes easy. Spin your legs
  • 20 minutes all-out, to determine the functional threshold power (FTP) over 60 minutes
  • 30 minutes easy cool down

If you repeat this test every month, you can track the development of your performance and modify your training if necessary. Unfortunately, this test only generates three values (CP0.25, CP4 and CP20), and your CP graph will be “thin”. Isn’t there a better way? There is! With the PerfectPace Critical Power chart.

PerfectPace Critical Power Chart

The PerfectPace Critical Power chart consists of three distinct components, designed to help you analyze your performance and plan your workouts and competitions. These are the CP model curve (dashed line), the best CP values you ever achieved (red-orange), and your best CP values in the date range you have selected (blue-green).

CP Model Curve

Based on your personal bests and using a physiological metabolism model, PerfectPace calculates your complete, personal CP curve (‘CP’ in the chart). This is the power output you should be capable of, even if you have not yet reached it in your training sessions or competitions.

For example, the model curve shows when the energy supply of your muscles switches from anaerobic glycolysis to aerobic glycolysis. This can be seen in the rapid power degradation typically between 20 seconds and 2.5 minutes.

As you can see, the CP model curve does not only show three CP values like from the described test protocol. Instead, you get your CP values for arbitrary time frames. A quick example how this can be useful: Assume you want to beat your personal best of 12 minutes for a particular incline. In this case, you can read your CP12 value from the model curve and attack the incline with this power. This ensures that you will be able to stay at this power level for the whole incline. If you still have it in you, you can even increase your power output right before the end of the incline.

Personal Bests

Besides the CP model curve, PerfectPace also calculates the best CP values you have ever achieved (‘CP-all’ in the chart). If you do high intensity interval training on some days, and work on your endurance on others, you will see that your personal bests will approach the CP model curve. There will be areas in which your personal bests match the CP model, and others where they will fall a bit short. This tells you where your strengths and weaknesses are and train accordingly.

CP Curve in a Custom Date Range

The third curve shows your best CP values in the date range you have selected, for instance your best average powers in the last month (CP-date range in the chart). With this curve, you can track changes in your training. If you do interval training in one year, and work on your endurance in the next, you can compare the results of your efforts by choosing suitable date ranges. In the example chart, you can see that the athlete trained in the CP20 power range and achieved personal bests there. Peak power output and long term endurance were not focus of the training in the selected date range.

If you want to analyze the results of a specific CP test or competition, you can select a date range of a single day. If your CP curve for the day stays below your personal bests or the model curve, then you know that you have not reached your full potential. On the other hand, if your CP curve touches the other two, then you have achieved new personal bests. You probably need to update your FTP and power zones in PerfectPace.

In the top right corner of the chart, you will find the CP60 values of the three curves. Labeled as ‘Model’ is the CP60 value of the model curve, ‘All workouts’ is your best CP60 ever, and ‘Date range’ is your CP60 in the selected date range.