Endurance Capacity: Power After 3,000 kJ Is What Really Decides Grand Tours

How Much of Your FTP Remains in the Fourth Hour

The FTP measured in a traditional lab setting is taken while your body is “fresh.” But the decisive attacks in a Grand Tour almost always happen after thousands of kilojoules of accumulated work. New-generation exercise physiology has therefore formally listed “durability” alongside VO2max and threshold as a determining factor of endurance performance—it measures the rate of power retention under fatigue.

Fresh vs. Fatigued Power Gap

Why Fatigued-State Power Has Predictive Power

Two riders may have the same FTP in a fresh state, but after accumulating 3,000 kJ, one drops only 3% while the other drops 12%—their fates in the third-week mountain stages will be worlds apart. A race doesn’t start when you’re at your strongest, so the “peak value” has less predictive power for results than the “rate of decline.”

Training Prescription: How to Build Durability

The core training logic for durability is to place key high-intensity stimuli after significant work has already been accumulated, rather than at the start of a session when you’re freshest.

• Fatigue-first sessions: Insert threshold or VO2max intervals in the latter part of a long aerobic ride
• Metabolic flexibility: Train fat oxidation and carbohydrate sparing to delay glycogen depletion
• Fueling strategy: High carbohydrate intake to sustain late-session output (see the high-carb feature)
• Fatigued-state testing: Periodically retest power after accumulated work to track the rate of decline rather than peak values

Measurement and Monitoring

Assessing durability requires a “fatigued-state power test”—for example, performing a maximal effort after a controlled amount of accumulated work, then comparing the drop against the fresh value. This rate of decline can be improved with training and becomes a tracking metric that reflects Grand Tour performance more closely than FTP.

The entire amateur training culture worships peak numbers, but the peak is the number least likely to occur at the moment racing happens. Durability reminds us of a cold truth: a Grand Tour isn’t about “who is strongest,” it’s about “who declines slowest.” Put your key sessions after you’re already tired, not while you’re still fresh—this one change in sequencing may get you closer to the podium than adding another ten watts to your FTP.

Related Reading

• Power Testing and Zone Setting for Triathlon: Metrics Beyond FTP
• The Scientific Validity of Functional Threshold Power (FTP): Correlation Studies with MLSS
• The Science Behind Power Training Zones: FTP and the Six Training Zones Explained
• Critical Power (CP) vs. FTP: Which Is Your True Threshold?