Your recovery has two speeds — that's why W-tau is not a single number
After an attack your power doesn't come back at one steady rate. There are two engines behind your recovery: one that recharges lightning-fast, and one that needs minutes. That difference decides whether you can still follow that second and third surge.
Rob Bohte, physician and coach · updated
Your attack battery — W′ in science — is the amount of work you can deliver above your Critical Power before you blow up. As soon as you drop below your CP, that battery recharges. The big misconception: that recharging does not happen at one fixed rate. Research shows recovery is best described by two simultaneous processes — a fast and a slow one — rather than by one. (Chorley & Lamb, 2022; independently confirmed by Caen et al., 2021)
In the first tens of seconds after an effort, part of your battery comes back lightning-fast. This is what lets you latch back on a few seconds after an attack.
The rest recharges far more slowly — a matter of minutes, not seconds. This determines whether, after a hard lap, you really have a full attack in your legs again.
Illustrative group values from Chorley & Lamb (2022): fast time constant ≈ 21 s, slow ≈ 388 s. The spread between riders is large (slow phase 200–716 s) — precisely why an average doesn't describe you.
Why this decides a race
Tucking into the wheel briefly after a surge mainly uses your fast phase — enough to latch on once. But that phase is small.
Going full gas again asks for your slow phase: then you really need minutes below your CP. Whoever doesn't have that is waiting on their slow engine after two attacks while the lead group rides away.
A single number can't capture this. “My recovery is 90 seconds” means nothing if half of that is in the first 20 seconds and the rest isn't complete until six minutes later. That's why W-tau is not a single number, but a profile with two speeds — and it's that profile that tells you how to ride a race.
And it varies per rider — measurably
How fast your two phases are is linked to your aerobic engine. In trained riders: the better your VO₂max and CP, the more you get back in a pause and the less your recovery drops off as efforts pile up. (Chorley et al., 2020) An app that sticks one curve on everyone misses that entirely. Your profile can be measured in a single targeted test session.
Want to know your two speeds?
The CP test is the first step: your Critical Power and W′ mapped, plus what it means for how you plan your races.