FTP and the W' Balance Model: Why Relying Only on FTP Loses Races in Attack Battles

FTP Isn’t the Whole Story

FTP (Functional Threshold Power) has been treated as the single metric of a rider’s ability for too long. It’s certainly important, but it only describes the ceiling of “how long you can sustain effort without blowing up,” and says nothing about “how much you can endure beyond that line.” The latter is described by W’ (read as W prime) in the critical power model—a finite, rechargeable energy battery that is depleted above threshold.

The Explanatory Power of the Two-Parameter Model

W’: The Finite Battery Above Threshold

Every effort above critical power (CP, often approximated by FTP) withdraws from the W’ battery; when you drop back below CP, W’ recharges at a certain rate. A rider with a lower FTP but a larger W’ and faster recharge may wear down a rider with a higher FTP but a smaller battery in a climbing battle full of repeated attacks.

Why Attacking Battles Are W’s Stage

Modern GC attacks and defenses are rarely pure steady climbing; they are repeated above-threshold pulses of “attack—chase—attack again.” Every time you follow an attack, you burn W’; whoever drains their battery first gets dropped. This explains why some riders with impressive FTP numbers fall apart when faced with repeated pace changes—their engine is big, but their battery is small and charges slowly.

Applications in Training and Racing

• W’ Monitoring: Use a real-time W’bal model to estimate remaining battery and avoid burning it all at once
• Recharge Training: Practice quickly dropping power back below CP between attacks to recover
• Tactical Pacing: Budget W’ as an allocation for the most critical attacks
• Individual Modeling: Each rider’s CP and W’ must be measured individually; they cannot be shared

What This Means for Amateur Riders

Amateurs chase FTP numbers excessively but rarely train the repeated use and rapid recharge of W’. In actual racing, wins and losses often come down to those few attacks you can or cannot follow, rather than steady output on long climbs. Understanding this will completely change the priorities of your periodized training.

Evaluating a rider with only FTP is like evaluating a race car with only engine displacement—you know how much horsepower it has, but not how many seconds of nitrous remain. The outcome of a race often isn’t decided on that sustainable line, but on that invisible battery above it that depletes and recharges. Training FTP lets you hold the pace; training W’ lets you survive the attacks.

Related Reading

• 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?
• The Critical Power CP Model: A Framework with More Explanatory Power Than FTP
• Critical Power and W’: A Two-Parameter Model Explaining How Much Longer You Can Hold On