When it comes to cycling and running, understanding your limits and how to push them can make a huge difference to your performance. That’s where the concepts of Critical Power (CP) and W Prime (W') come in. These terms might sound technical but they’re essentially tools to help you figure out how hard you can go, how long you can sustain it and when you need to recover. Let’s break it down in simple terms:

Critical Power (CP):

Think of CP as the line between what you can do forever (steady effort) and what you can only do for a little while (hard effort). It’s the power you can sustain for a long time without completely burning out.

For cycling, this is measured in watts.
For running, there’s a similar concept often called Critical Speed, which is measured in pace or speed.

If you stay below your Critical Power you can keep going for hours. Go above it, and you’re tapping into a finite reserve of energy that you can only sustain for a short period before you have to slow down or stop.

W Prime (W’):

W Prime is like a ‘battery’ of extra energy you can use when you go above your Critical Power. It’s your anaerobic reserve—basically, your ability to go hard in short bursts.

When you sprint up a hill, surge during a race, or try to hang on to a fast group, you’re using your W Prime.
But once it’s used up, you’re cooked, and you’ll need to back off (drop below CP) to ‘recharge’ it.

How They Work Together:

If you’re below CP your W' doesn’t drain and you can go for a long time.
If you go above CP you start draining your W'. The harder you go, the faster the battery drains.
To recover and recharge your W' you have to drop back below CP.

How to Train and Improve CP or W':

The training will be different depending on which one you’re trying to improve:

To Improve Critical Power (CP):

If you want to perform better in long-distance events or sustained efforts, focus on raising your CP. This means improving your ability to hold a steady, higher power for longer.

Workouts to try:

Threshold intervals: Ride or run just below CP for 10–20 minutes with short recovery periods.
Long steady-state efforts: Spend extended time riding or running at 85–95% of your CP.
Endurance training: Build your aerobic base with longer, low-intensity rides or runs.

To Improve W Prime (W'):

If you want to boost your ability to sprint, surge, or recover faster after hard efforts, focus on increasing your W' or making your anaerobic battery last longer.

Workouts to try:

Short, hard intervals: Do all-out efforts lasting 30 seconds to 2 minutes, with long recoveries (e.g., 6 x 1-minute sprints with 4–5 minutes of rest).
Hill sprints: Sprint uphill for 15–60 seconds, then recover on the way back down.
Tabata intervals: Alternate between 20 seconds of max effort and 10 seconds of rest for 4 minutes.

Which Should You Focus On?

If you’re training for events like marathons, time trials or IRONMAN races, prioritise improving your CP to sustain higher efforts for longer.
If you’re doing short-course races, crits, or races with lots of surges (like road races), focus on developing your W' so you can handle repeated hard efforts and recover quickly.

By tailoring your training to focus on either CP or W', you can make specific improvements that align with your goals and race demands. Think of it like tuning your engine - whether you need more cruising efficiency or better nitro boosts, targeted training can help you get there.

Exploring Athletic Performance with Dr. Phil Skiba

In this Fitter Radio Triathlon Podcast episode, Dr. Phil Skiba, a leading sports scientist known for his work on the Breaking 2 Project, unpacks the concept of Critical Power (CP) and W Prime (W’). He also discusses individualized training, the importance of balanced nutrition and strategies for injury prevention and ‘Long’ COVID recovery. This episode is packed with insights to elevate athletic performance. Click on the image to listen.

Bevan McKinnon / December 2024

Understanding Critical Power (CP) and W Prime (W')