Same FTP, completely different riders
You ride with your mate Jim. You've both been at it for years, and over time things have converged so that your FTP is the same. When Jim said his was 270W and yours was 250W, you buckled down, got the threshold intervals done that he told you about, and six weeks later yours hit 270 too. You're both the same weight, so, rightly, you thought you'd finally be battling each other up the local hill. But every time, every time you hit the climb, Jim rides away from you.
OK, look, I've no idea if you actually have a friend called Jim you train with. But what my imaginary riders are going through isn't imaginary. It's frustrating. You've been led to believe that having the same FTP and weight as another rider makes you just as good as them (or just as bad — glass half full or half empty, your call). It doesn't.
Here's what's actually going on.
That hill of yours is only a few minutes long. You'd assume that makes it a test of engine size, who's got the bigger aerobic ceiling. But at a few minutes, both you and Jim are riding above your FTP. And the moment you're over threshold, the thing doing the work isn't your FTP at all. It's your spare battery.
Every rider has one. The proper name is FRC — functional reserve capacity — if you're working off FTP, or W' ("W-prime") if you prefer critical power. (I'm metric-agnostic; use whichever you like.) Think of it as a finite battery sitting on top of your FTP. You can drain it fast in a 60-second all-out effort, or bleed it slowly over a 10-minute max, but there's only so much in there, and when it's gone, it's gone. You're still turning the pedals with your FTP underneath; the battery just determines how hard, and how long, you can go above it.
And here's the thing: batteries come in very different sizes. Say your FRC is around 12.5kJ and Jim's is 18kJ. Same 270W FTP, same weight, but on that climb you're both over threshold and Jim's battery simply holds more charge. It lasts longer before it's flat. That's it. That's why he rides away not a bigger engine, a bigger reserve.
Once you dip back below FTP, the battery recharges. How fast it recharges depends on your aerobic fitness and this is a quiet an issue in training software, because every platform models that recharge with the same numbers for everyone, when in reality it differs from person to person. Yours might come back quicker than Jim's. None of the apps are telling you that (the software apps use a standard recharge, because ultimately the maths is complicated and you need additional data).
And if you completely empty the tank? Dead legs, and a long wait to get anything back. In a recent race I emptied mine entirely and rode around on useless legs for a good while afterwards. (Some people think I always have useless legs all the time. That's also fair).
So if it isn't just FTP, what should you be looking at?
When Dr Coggan gave us FTP — a genuinely brilliant idea — he never meant it to be the only number. My preference as a coach is to look at MAP (your best 60 seconds of a ramp test to exhaustion), FTP or CP, your 5-second sprint, and your 60-second max. Throw in 5-minute power if you like. Together they give you a proper picture of a rider.
And there's a shortcut hiding in two of those. Compare your FTP to your MAP: (FTP ÷ MAP) × 100 and you get a strong hint at whether your battery is big or small. Mine sits around 77%. That's high: my FTP is close to my ceiling, which means my FRC is small and big accelerations really aren't my thing. That's not a guess, it's my life, I race road and crits, and it's exactly what I have to train around.
A lower percentage tells the opposite story: a bigger gap between FTP and MAP, a bigger battery, a rider who can rattle off short efforts all day, but who might find a flat-out time trial utterly miserable. Neither is better. It depends entirely on what your event asks of you. A small battery is no handicap at all in a time trial or a triathlon; those events never ask you to empty it.
So, you'd assume a small-battery rider like me gets shelled the moment the road tilts. And early on, I do. If a race goes bonkers hard from the gun (I really hope nobody I race with is reading this), I can get spat out the back.
But here's the second thing FTP hides. My battery's small yet I'm rarely distanced. Because although there isn't much in it, I seem to recharge it quickly and cope with repeated efforts better than riders carrying much bigger reserves. Once a race settles and everyone starts burning through their FRC, I come back to them. Same FTP, similar FRC even and still a completely different rider, because durability and recharge are an axis all of their own. (That's a whole article for another day.)
Which is really the point. The next time someone asks about your FTP, remember it was never the whole story: it's one number in a rider made of several. The real question isn't what your FTP is. It's where it sits relative to your ceiling, and whether you're a big-battery rider who fades or a small-battery one who lasts.
Want to find out which one you are? Our power calculator will show you exactly how you stack up across the board — it's genuinely the most comprehensive one known to man ;-) No, really: www.cyclecoach.com/calculator