English Endurance
Fuel Based Pacing Calculator
Model the power ceiling imposed by fuel availability across long events. As duration grows, sustainable power is limited less by aerobic capacity than by the rate carbohydrate can be delivered and oxidised alongside stored glycogen and fat.
Athlete & fuelling inputs
Sustainable power ceiling by duration
Power ceiling — watts by duration and intake rate
Method & assumptions
- Fuel-limited power. Total substrate oxidation is the sum of ingested carbohydrate, endogenous glycogen spread across the event duration, and fat oxidation. Converting that energy flux to mechanical power uses the mechanical efficiency setting.
- Critical power cap. Sustainable power is capped at 88% of FTP, since no amount of fuel raises the ceiling above what the aerobic system can hold for multi-hour durations.
- Fat oxidation scaling. Fat contribution falls as relative intensity rises — held at baseline below 60% of FTP, tapering to zero at 90%. The model solves this iteratively because intensity and fat oxidation are mutually dependent.
- Fat-oxidation default. Estimated from absolute VO₂max derived from 5-min power (Achten & Jeukendrup 2003 scaling). Adjust the slider if the athlete has tested fat-oxidation data.
- Body mass affects only the displayed VO₂max estimate in ml·kg⁻¹·min⁻¹ — it does not enter the power calculation.
Mechanical efficiency is set to 20% by default, with a range of 18–22%. This is the fraction of metabolic energy that becomes mechanical work at the crank; the remainder is liberated as heat. Trained cyclists typically fall near the middle of this range, and efficiency varies modestly with cadence, intensity, and muscle fibre composition. Higher efficiency means the same fuel supports more power.