So you’ve been training with power and now you want to run a race. What power should you target and for what duration?

For estimating your various race day power targets, you can use the table provided on Stryd’s Facebook Page (a post from June 2, 2017) or you can use the Riegel prediction formulas based on known distance and speed or known power and time. It should be noted that everyone’s fatigue factor and running effectiveness values are different, so the Riegel prediction formulas may provide closer estimates, although it takes a little more work to develop the estimate.

Methods to estimate your race power:

  • Stryd’s table
  • Riegel Prediction Formula – refined with running effectiveness, see the spreadsheet below to develop your personal Riegel fatigue factors and running effectiveness metric


The Stryd table:

To use the table, multiply your most recent 10k average power with the percentage from the table based on your target race distance.


Example 1: 10k Power = 300 watts, target race distance = 5k

Target race power = 300 watts x 103.8 percent = about 312 watts

Example 2: 10k Power = 300 watts, target race distance = 21.1k

Target race power = 300 watts x 94.6 percent = about 284 watts

Stryd Power Scaling

The Riegel Formula:

Using this equation, you can estimate your target power based on your CP/FTP and target race duration.

Target Power = CP/FTP x (Target time/60)^fatigue factor


CP/FTP = critical power/functional threshold power

fatigue factor = typical values are -0.06 to about -0.08, use -0.07 as an average or use the spreadsheet below


Example 1: CP/FTP = 300 watts, target time = 22 minutes (5K)

Target power = 300 x (22/60)^-0.07

= 300 x 1.07

= 322 watts

Example 2: CP/FTP = 300 watts, target time = 180 minutes (Marathon)

Target power = 300 x (180/60)^-0.07

= 300 x 0.93

= 278 watts

Refining your target power:

You can further refine your target power by dividing it with your typical running effectiveness (RE) for the predicted time duration. Running effectiveness can be tracked every workout if you run with Stryd.

Example: Refined target power for 5k race with 0.97 RE = Target power / RE = 322 watts / 0.97 = 332 watts

Below is a spreadsheet for developing your personal Riegel “Fatigue Factor” and running effectiveness metric for race predictions.

You need your power, speed, and distances for several times (e.g. 3min, 10min, 20min, 40min, 60min, 90min, etc.) . These values can be collected from your power-duration curve and critical velocity curve in Golden Cheetah or other software.

Reference: Ron George Blog Post

Personal Riegel Spreadsheet
CP 3 minute example
CV 3 minute example