Should You Pedal or Coast Down a Hill? The Answer Lies in Critical Power and W′

It’s a scenario every cyclist knows: You’ve just crested a climb—legs screaming, lungs burning—and now you’re staring down a long descent. The question: Do you keep pedaling to hold your speed or tuck and coast to recover?

While it might seem like a matter of comfort or preference, the truth is rooted in something deeper: a fascinating model of human performance built around Critical Power (CP) and W′ (W prime).

Let’s unpack what that means, and how it can help you make smarter decisions on every ride.

What Is Critical Power (CP)?

Critical Power is the theoretical power you can sustain for a long time without fatigue building up in an unsustainable way. It’s the tipping point between steady-state aerobic effort and anaerobic effort.

Think of CP as:

• Your "fatigue threshold"

• The power level at which energy supply meets demand

• The line between controlled and explosive efforts

When you ride below CP, you're mostly using your aerobic system. You could ride at this power for a long time (within reason).

But when you ride above CP, you're borrowing energy from your limited anaerobic battery—this is where W′ comes in.

What Is W′ (W prime)?

W′ (pronounced “W prime”) is your anaerobic work capacity. It’s a finite reservoir of energy you can use to push above Critical Power—for example:

• During a sprint

• Up a short, steep hill

• When attacking out of a group

It’s measured in joules (J) and represents the total amount of work you can do above CP before you're exhausted.

Once your W′ is used up, you can’t sustain efforts above CP again until you’ve recovered some of it—usually by riding below CP. The lower the power during recovery, the faster W′ refills.

Pedal or Coast?

Let’s go back to the original question: Should you pedal or coast down a hill?

The answer is: It depends.

We simulated multiple scenarios using real CP and W′ models. Here's what we found:

Descent Length	Climb Type	Best Strategy
1–2 km	Punchy/climb soon	Coast
3 km	Balanced/mixed	Toss-up
4–5+ km	Sustained effort	Pedal

✅ If a short, steep climb follows:

Coast. This allows you to recover a large portion of your W′, so you hit the climb with a full anaerobic tank and can go harder for longer.

✅ If a long climb or flat section follows:

Pedal. Even at a light to moderate effort, you’ll descend faster, and if you're going to be sitting at or near CP for several minutes, you won’t rely on W′ much anyway.

How to Determine Your CP and W′ as an Amateur Rider

You don’t need a lab or a coach to get a solid estimate of your CP and W′. Here are a few practical methods:

1. Use Field Testing

Do all-out efforts at multiple durations:

• 3-minute max effort

• 12-minute max effort

• 20-minute max effort

Record the average power for each. Then, use an online Critical Power calculator (like from Golden Cheetah or Intervals.icu) to plot a power-duration curve and estimate your CP and W′.

2. Use a Power Meter + Analysis Tool

Apps like WKO5, Golden Cheetah, Xert, or Intervals.icu will estimate CP and W′ over time using your historical ride data.

The more all-out efforts you have at different durations, the better the estimates become.

3. Ramp Tests or Step Tests

Some platforms offer guided ramp tests that estimate threshold values and use those to derive CP. While not perfect, they can give a ballpark figure.

What's a Typical CP and W′?

Rider Type	CP (W)	W′ (J)
Amateur Recreational	180–230	5,000–9,000
Trained Club Rider	230–280	8,000–12,000
Elite/Pro Rider	300+	15,000–25,000+

Why This Matters

Every ride, race, or climb is a mix of energy management. Knowing your CP and W′ helps you answer questions like:

• Can I attack now and still recover for the final hill?

• Should I let others go and coast to refill my tank?

• Why did I blow up on that climb when I was “only” pushing 320 W?

And of course…Should I pedal or coast down this descent?

Now you have the answer.