In simple terms, it represents your current fitness and is measured in watts (W) or watts per kilogram (W/kg).
Functional threshold power (FTP) and critical power (CP) can be used interchangeably in a running context. So where you see FTP used, CP can be used or vice versa.
CP/FTP is the cornerstone metric for training and running with power. It’s used to determine training zones and target power on race day.
That’s why having an accurate CP is vital to effective training and should be re-assessed every 4-6 weeks.
CP can be estimated using two primary methods:
- A critical power test.
- Scientific modeling with Stryd’s auto CP, WKO, or Golden Cheetah.
Comparing Critical Power
When comparing CP to other runners (or tracking yours over time), W/kg should be used instead of raw watts. For example, no comparison can be made between two runners with a critical power of 220 W (Runner A) and 300 W (Runner B). However, if you know Runner A weighs 55 kg and Runner B weighs 75 kg, you can compare their W/kg.
\text{Runner A: }\frac{\text{220 W}}{\text{55 kg}} = \text{4.18 }\frac{\text{W}}{\text{kg}} \text{Runner B: }\frac{\text{300 W}}{\text{75 kg}} = \text{4.00 }\frac{\text{W}}{\text{kg}}All things being equal, Runner A will be faster than Runner B at critical power because they have a higher W/kg.
And keep in mind, W/kg varies depending on intensity. So you can’t compare your W/kg at 5k effort to someone else’s W/kg at marathon effort. Comparisons are only valid at similar intensities.
Classifying Your W/kg
The table below is shared in the book The Secret of Running by Ron Van Megen and Hans Van Dijk.
Look up your W/kg at critical power and it’ll show you how you compare to world record holders, competitive regional runners, untrained runners, etc. For example, if you’re a male with a W/kg around 3.8 then you might be a competitive local runner.
Note: While the table is specific to cycling, it translates well to runners.
| Classification | Men (W/kg) | Women (W/kg) |
| World Record | 6.4 | 5.7 |
| International | 5.8 | 5.1 |
| National | 5.1 | 4.6 |
| Regional | 4.5 | 4.0 |
| Local | 3.8 | 3.4 |
| Fair | 3.2 | 2.8 |
| Untrained | 2.6 | 2.3 |
| Poor | 1.9 | 1.7 |
| Very Poor | 1.4 | 1.1 |