FTP Is Not a Personality Trait.

An athlete messaged me at eleven at night once to tell me his FTP had dropped four watts. Four. He had tested at the end of a week that included a house move, a sick child and two nights of about five hours' sleep, and he wanted to know what had gone wrong with his training.

Nothing had gone wrong with his training. Something had gone right with his life, in the sense that he had survived a hard week. The number just did not know that.

FTP is a measurement of one thing on one day. It is not a report card on you.

What the Number Actually Is

Functional threshold power is, roughly, the highest average power you could hold for an hour. In practice almost nobody tests it by riding flat out for an hour, because it is miserable and because you do not need to.

What matters is what it governs. Every training zone you use is calculated from it. Your race power targets come from it. Intensity Factor, Training Stress Score, the whole apparatus of load tracking sits on top of it. Get FTP wrong and every session you do afterwards is prescribed at the wrong intensity, which is why I care about testing it properly and why I care much less about the number itself.

I use FTP as a ruler, not a trophy. A ruler that is four millimetres out will quietly ruin everything you measure with it. That is the only reason his four watts could have mattered, and in his case they did not, because a four watt change is noise.

What It Cannot Tell You

Here is where I see most athletes go wrong. FTP is a single point on a very large curve, and the curve is what you actually race on.

It tells you nothing about how long you can hold ninety percent of it. Two riders with identical FTPs can be completely different animals. One falls apart after forty minutes at threshold, the other sits just underneath it all day. In a 70.3 you are riding at perhaps seventy five to eighty percent of FTP for two and a half hours, and your ability to do that is durability. FTP does not measure it.

It tells you nothing about what you can do after three hours. An athlete's power profile at the end of a long ride can look nothing like the fresh one. Fresh numbers are the ones we talk about. Fatigued numbers are the ones that decide races.

And it tells you nothing about what any of it costs. Two athletes can hold the same watts, one at a heart rate of 148 and one at 165. Same output, different price. I want to know the price.

How I Actually Test It

I use a twenty minute test for most people and take ninety five percent of the average. Not because it is the most accurate protocol in the literature, but because it is repeatable and athletes will actually do it. Repeatability is worth more than precision here. A test you dread is a test you avoid, and a number from six months ago is worse than a slightly imperfect number from Tuesday.

The rules I give my athletes are mostly about controlling everything except the legs.

Same time of day. Same trainer or same road. Same fan, same fuelling, same warm up. Not after a hard week, not the morning after a bad night, not in the middle of a life event. If your readiness is on the floor, you are not testing your fitness, you are testing your resilience, and those are different questions.

Then retest every six to eight weeks. More often and you are measuring noise. Less often and you are training in zones that stopped being true a while ago.

The Thing I Wish More People Understood

A rising FTP is not automatically progress, and a falling one is not automatically failure.

I have had athletes whose FTP stayed flat for an entire season while their race times came down by minutes, because what improved was durability, pacing discipline and the ability to run off the bike. The engine did not get bigger. They got better at using it.

I have also had athletes push FTP up ten percent in eight weeks and race worse, because the way they got there was a block of intensity that left them arriving at the start line already emptied out. The number went up. The athlete went down.

So when someone shows me a new FTP, my next question is never what the next target is. It is: what did it cost, how do you feel, and can you hold seventy five percent of it for two hours without falling apart? That last question is the race.

Where the Number Belongs

I want FTP to be boring. A quiet reference figure sitting in the background, making sure Tuesday's intervals are actually intervals and Sunday's ride is actually easy.

The moment it becomes an identity it starts making decisions for you. You test when you should not. You chase it in weeks when the point was to build a base. You take a four watt drop personally at eleven at night, when what you actually needed was to go to bed.

I told him to sleep, eat properly for a week and retest in ten days. He gained eleven watts. He had not got fitter in ten days. He had just stopped testing a tired man.

The Bottom Line

Test it properly, under conditions you can repeat, when you are not wrecked. Use it to set your zones, then stop looking at it. Judge yourself on durability, on what the power costs your heart rate, and on what you can do in hour three, because that is what the race is made of.

The number is a ruler. Do not let it become a mirror.