What W Prime (W') Actually Is

If Critical Power (CP) is the line between sustainable and unsustainable effort, W Prime (W') is what sits above it. Think of it as your anaerobic work capacity. The finite reserve of energy that fuels every attack, surge, and sprint before you’re forced back under CP.

Measured in joules (J) or kilojoules (kJ), W′ acts like a battery. Deplete it, and you can’t go above CP again until it recharges. That’s why two riders with the same CP can perform so differently: the one with more W′ can survive more explosive racing, while the other may falter sooner.

How It Works in Practice

Every time you go above CP, you burn into W′. The higher you go, the faster it drains. When you drop back to CP or below, W′ begins to recharge. Though the recovery is slow and never fully “restores” in a race.

The Math Is Simple

W′ = (P − CP) × t

P = your power output (watts)
CP = your critical power (watts)
t = time spent above CP (seconds)

Example:

• CP = 300 W

• W′ = 20 kJ

• Riding at 400 W (100 W above CP) for 200 seconds:

(400 − 300) × 200 = 20,000 J = 20 kJ → full depletion of W′

This means you can calculate how much “fuel” you have left when riding above CP.

Coaches Use This For:

• Race predictions — Can you bridge to that group before running empty?
  
  
  

• Time trial pacing — How much can you overshoot CP on climbs before paying for it?
  
  
  

• Interval design — Structuring reps to drain and partially recharge W′ for race-specific training.

  
  
  

Why It Matters in Racing

W′ is more than a lab concept. It’s often the deciding factor in unpredictable, high-stakes moments.

• Attacking on a climb: Knowing your W′ gives confidence to launch at the right moment; you know how long you can sustain above CP before you “red-line.”
  
  
  

• Bridging across a gap: If the numbers say you’ll burn through W′ halfway across, you may decide to sit in and wait for a better moment.
  
  
  

• Surviving repeated surges: In gravel and MTB, where the pace is unpredictable, the balance between W′ expenditure and recovery often decides whether you stay with the leaders or get dropped.

In short, racing isn’t just about CP. It’s about how wisely you spend and recharge your W′ battery.

W Prime & Vekta

Inside Vekta, CP and W′ sit at the core of the performance model. That means the numbers don’t just live in theory; they get turned into insights you can apply on the bike.

Where FTP gives you a single threshold, CP + W′ show you the whole picture: not just where the line is, but how much room you have above it, and how quickly you can come back after crossing it.

It’s a way to plan sessions with more intent, pace races with more confidence, and make decisions that aren’t guesswork.

In practice, W′ becomes another tool you can lean on, and with Vekta, it’s built right into the system.

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