What is W' (W-prime)?

W' represents the finite amount of work (in Joules or kJ) that can be performed above Critical Power before complete muscular exhaustion occurs.

Updated: August 2026 • Verified v1.2

Critical Power (CP) & W' Anaerobic Work Capacity Calculator

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W(t) = CP * t + W'; CP = (P2*t2 - P1*t1) / (t2 - t1); W' = (P1 - CP) * t1

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Understanding Your Results

Computes Critical Power (Watts and W/kg) and W' (kJ), models predicted power for durations from 1 to 60 minutes, simulates time-to-exhaustion at supra-CP power, and provides CP-calibrated training zones.

Practical Guidance & Next Steps

Critical Power represents the highest power output that can be maintained in a metabolic steady state without continuous depletion of glycogen and accumulation of intramuscular lactate. Any effort above CP draws directly on the finite W' battery.

What is this?

A sports physiology calculator that computes Critical Power (CP) and anaerobic work capacity (W') using the Monod and Scherrer work-time model.

How does it work?

1. Enter athlete weight and all-out power/duration for two time trials (e.g. 3 min and 12 min). 2. View Critical Power (Watts, W/kg) and W' capacity in kJ. 3. Test time to exhaustion for attacks and explore CP-calibrated training zones.

Why use it?

More physiologically rigorous than standard 20-minute FTP tests for pacing breakaways, time trials, and interval workouts.

Technical Scope & Calculation Limitations

Uses the classical Monod & Scherrer 2-parameter hyperbolic/linear work-time model.

Frequently Asked Questions

While FTP is an empirical estimate of 1-hour power (often estimated as 95% of a 20-minute test), Critical Power is a mathematically derived parameter representing the boundary between steady-state and non-steady-state oxidative metabolism.

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