FTP (Functional Threshold Power)
The highest average power, in watts, you could hold for about an hour: cycling's core intensity benchmark.
Functional Threshold Power (FTP) is defined as the highest power you could sustain, on average, for roughly an hour of maximal effort. It's the reference point cycling training is built around. Every zone, from easy recovery riding up through anaerobic efforts, is usually expressed as a percentage of FTP. It's also the denominator in the Training Stress Score formula: an hour at FTP is defined to score exactly 100 TSS.
How it's actually tested
A true one-hour, all-out test is brutal and rarely done in practice. Most athletes estimate FTP from a shorter, more repeatable protocol instead. One option is a 20-minute maximal effort, with the result multiplied by roughly 0.95 to approximate the one-hour number. Another is a ramp test, which estimates it from the power curve as effort builds to failure. Both are estimates, not the literal one-hour value, and different protocols can give slightly different numbers for the same athlete on the same day.
Why it needs retesting
FTP isn't a fixed trait. It rises with training and falls with detraining, typically within six to eight weeks. Training off a stale FTP number means every zone calculated from it is off too. A "threshold" interval done at an outdated FTP might actually be tempo effort for someone who's gotten fitter, undertraining the exact system the workout was meant to target. Retesting periodically, especially after a focused block, keeps the whole zone structure honest.
Where it fits in triathlon
FTP is cycling-specific by definition, since it's power-based. But the same idea, a threshold intensity everything else gets scaled against, has running and swimming equivalents: threshold pace and critical swim speed. A triathlete juggling all three needs the concept in each discipline, not just on the bike. Race pacing across a triathlon depends on managing effort relative to each sport's own threshold, not one universal number.