Critical Power Testing

One of the methods that's typically mentioned for determining your Functional Threshold Power is through the use of Critical Power Testing.

Before launching into testing for it, let's define just what it is, this Critical Power. You'll find the term Critical Power tossed all over the place to describe one power level or another, but it's really only meant to describe one particular condition. Critical Power is simply the maximum sustainable power output you can maintain for a given amount of time. How many watts can you output for 1 minute? For 3, 5 or 15 minutes? You can probably make a lot more watts for 1 minute than you can sustain for 10. Critical Power is the curve defined by that maximal power output per the number of minutes of duration.

Defined like this, Critical Power is different from Functional Threshold Power. Functional Threshold is constant over duration and is typically associated with 60 minute power. The longer the duration, however, the closer Critical Power and Functional Threshold Power converge.

The job of Critical Power testing is to use a couple of short Critical Power tests to estimate power output for a longer term, such as 60 minutes. Because Functional Threshold Power and Critical Power at 60 minutes are very close, an estimate of CP60 (Critical Power at 60 minutes) is a good proxy for Functional Threshold Power.

So how does Critical Power testing work?

The most frequently cited testing protocol is the Monod-Scherrer testing method. The test is in two parts. Both parts involve outputting as near constant wattage as possible. The parts differ in their duration. One test should be run for 3 minutes, the other for 12. Watts should be held as constant as possible for each test, and at a level beyond which you cannot complete the 3 or 12 minutes, but not less.

No mistaking, these tests are painful. They are tests of maximal output. Both require plenty of motivation. Many cyclists don't do both tests in a single day. To determine Critical Power, input your 3 and 12-minute wattage levels into our Critical Power calculator. It will instantly tell you your Critical Power.