The W' (W Prime) Model in Cycling: Training Implications of Anaerobic Work Capacity

Introduction

Many cyclists are familiar with FTP (Functional Threshold Power) but feel unfamiliar with “W’ (W Prime).” In fact, W’ is the second core parameter in modern power training that cannot be ignored. W’ represents the total amount of anaerobic work you can perform above your Critical Power (CP), measured in Joules. When you push hard in the final 500 meters of a climb or sprint with everything you have 200 meters before the finish line, you are consuming your W’ reservoir. Understanding W’ is not just academic knowledge; it is a powerful tool that allows you to make precise decisions during races and training.

What is W’? The CP+W’ Two-Parameter Model

The Relationship Between CP (Critical Power) and W’

CP and W’ together form the two descriptive parameters of the Power-Time (P-t) curve. CP can be understood as a “sustainable limit”—theoretically, you will not be exhausted riding below CP for a long time, while every second spent above CP consumes your W’ reserves.

The formula is as follows:

W’ consumed = (Output Power − CP) × Time (seconds)

Conversely, when power is below CP, W’ recovers at a certain rate (recovery rate). This is why briefly reducing your intensity after a high-intensity attack allows you to “recharge” and exert force again.

Typical Value Ranges for W’

Note: A high W’ does not mean a high FTP; the two can be developed independently. A rider with a high W’ but low CP excels at short bursts but cannot maintain high power for long periods; a rider with a high CP but low W’ is a “diesel engine,” suitable for long-distance time trials.

How to Measure W’

The Three-Max-Power Test Method

The most common method is to perform three all-out tests of different durations and then use non-linear regression to fit CP and W’. Common duration combinations include:

• 3 minutes / 5 minutes / 12 minutes all-out effort
• 2 minutes / 5 minutes / 20 minutes all-out effort

There must be sufficient recovery between each test (at least 48 hours), and every segment must be your maximum effort for that day, otherwise, the fitting error will be significant.

Automatic Estimation Using Power Meter Software

Platforms like TrainingPeaks and intervals.icu can automatically estimate CP and W’ based on the best power curves (Power Curve / MMP curve) from your past training records. However, the error is larger when data is insufficient; it is recommended to have at least 3 months of power training records.

Methods for Training W’

The Core Logic of Increasing W’

The essence of W’ is muscle phosphocreatine (PCr) reserves, anaerobic glycolysis capacity, and the recruitment efficiency of fast-twitch muscle fibers. To effectively improve W’, you need targeted high-intensity stimulation above CP, allowing muscles to adapt to the repeated “discharge and recharge” cycle.

Examples of effective W’ training sessions:

• 30/30 Intervals: 30 seconds at ultra-high intensity (150%+ CP), 30 seconds of active recovery, repeat 10–20 times.
• 1-Minute Sprint Sets: 1 minute at 130% CP, 2 minutes of recovery, repeat 8–12 times.
• Micro-bursts: 10 seconds all-out, 20 seconds light pedaling, continuous for 10–15 minutes without stopping.
• Race Simulation Sets: Simulate race climbing attacks, 5–8 sets of 90–120 seconds at above-CP power, with 5 minutes of full recovery between sets.

Synergistic Training of W’ and CP

Increasing CP (i.e., FTP) also indirectly makes W’ “more durable” because the ratio of daily riding power to CP decreases, and the consumption rate slows down. Therefore, do not train W’ in isolation; basic aerobic volume and threshold training remain the foundation.

Application of the W’ Model in Race Strategy

Calculating the Timing of Climbing Attacks

Suppose your W’ = 18,000 Joules and CP = 260 Watts. An opponent attacks 3 minutes before the end of a climb, requiring you to output 320 Watts to keep up. The W’ consumed during this time is:

(320 − 260) × 180 seconds = 10,800 Joules

You have 7,200 Joules left. If there are 2 minutes left to the summit, maintaining 280 Watts results in an additional consumption of (280−260) × 120 = 2,400 Joules. Calculating this way shows you can make it to the finish line, but you are close to the limit—a slight mistake could lead to a drop in speed. This type of advance calculation allows you to make more rational decisions during a race.

Real-time Application of Recovery Rates

W’ recovery is not linear; research shows that the further below CP you are, the faster you recover. Briefly dropping to 60–70% of CP during a race allows W’ to replenish faster, which is the scientific basis for why riders intentionally “soft pedal” during climbing segments.

Practical Advice

• Test W’ Regularly: Re-run an all-out test every 8–12 weeks to observe if W’ improves with training.
• Don’t Just Look at FTP: W’ determines whether you can “kick” one more time at a critical moment in a race; it is just as important as FTP.
• Use intervals.icu to Track W’ Reserves: Some platforms can now display real-time W’ consumption during rides.
• Schedule W’ Training in the Middle of the Cycle: Build an aerobic foundation during the base period, and place specialized W’ training 8–12 weeks before the race.
• W’ Decreases in Hot Weather: When training in Taiwan during the summer, lower your intensity expectations appropriately.

Conclusion

The W’ model allows us to describe “explosive power reserves” with more precise language. It is not just an advanced tool for athletes—any cyclist with a power meter can benefit from it. Knowing your W’ is like knowing how much fuel is left in your tank, allowing you to stop relying solely on “feel” during the final attack before a summit or a sprint finish, and instead make decisions supported by data. Next time you train, try to arrange a few short sprints above CP to experience the reality of W’ depletion and replenishment.

Related Topic Reading

• Cycling Anaerobic Capacity W’ Training: The Science and Development of Explosive Power
• Critical Power and W’: A Two-Parameter Model Explaining How Much Longer You Can Last
• The Complete Guide to CP and W’: A Hyperbolic Model That Understands Pacing Better Than FTP, From Wuling to Criterium Racing
• Critical Power (CP) vs. FTP: Which Is Your True Threshold?