Everyone watches FTP. It's the number that gets quoted at the coffee stop, the one that goes up on the whiteboard, the one people retest every six weeks hoping for good news. And I get it — it's a single, clean figure that feels like a verdict on your fitness.
But FTP is a slow mover, and it can sit flat for weeks while real change is happening underneath it. The number that shows you that change — the one almost nobody looks at — is Efficiency Factor. If FTP is the headline, EF is the story underneath it, and on a base block it's often telling you good news long before your threshold catches up.
What Efficiency Factor actually measures
Efficiency Factor is simple. It's your Normalised Power for a ride divided by your average heart rate for that ride. Watts per heartbeat, near enough.
Say you ride a steady two hours at a Normalised Power of 220 watts and an average heart rate of 142. Your EF for that ride is 220 ÷ 142, which is about 1.55. On its own that number means almost nothing. Its entire value is in what it does over time.
Because here's the mechanism. As your aerobic base improves — as you build mitochondrial density, capillary networks, fat-burning capacity, all the slow adaptations that easy riding drives — you produce the same power at a lower heart rate. Or more power at the same heart rate. Either way, watts per heartbeat goes up. So a rising EF on the same kind of ride is a direct, measurable readout that the aerobic engine is getting bigger. That's the engine that everything else sits on. Professor Seiler's whole body of work on polarised training is, at its core, about building that base efficiently — and EF is how you check it's actually being built.
Track it on a benchmark, not on everything
This is where most riders go wrong with EF, so read this part twice: the number is only meaningful when you compare like with like.
EF on a flat-out race? Meaningless. EF on a stop-start ride through town with thirty sets of traffic lights? Meaningless. EF on a hilly ride where you were soft-pedalling the descents? Noisy and hard to read. The number assumes a steady, sustained effort, and it falls apart the moment the ride is variable.
So you need a benchmark. Pick one repeatable ride — ideally a steady zone 2 endurance ride of 60 to 120 minutes, or a steady tempo effort, on roughly the same route or the same trainer session, fuelled the same way, in similar conditions. That's your test piece. You ride it regularly through a block, and you watch the EF on that ride climb. TrainingPeaks calculates EF for every ride and interval automatically, and lets you chart it over time, so once you've decided on your benchmark the tracking is no work at all — you just glance at the trend.
A realistic picture: at the start of a winter base block your benchmark zone 2 ride might come back at an EF of 1.55. Eight to twelve weeks of consistent aerobic work later, the same ride at the same heart rate is coming back at 1.68 or 1.72. Your FTP test might not have moved much in that time. But the EF trend is telling you, unambiguously, that the base did its job. That's the reassurance that keeps you riding easy when the ego wants you to ride hard.
Pair it with decoupling
EF tells you how efficient you were on a given day. Its close cousin, aerobic decoupling, tells you how well that efficiency held up within the ride — and TrainingPeaks shows it as Pw:Hr.
Decoupling compares the power-to-heart-rate ratio in the first half of a ride against the second half. If you held 200 watts at 140bpm early and it took 148bpm to hold the same 200 watts late, your heart rate drifted up — your efficiency decoupled. Under about 5% drift is the marker of genuine aerobic durability: the system held steady for the whole ride. A bigger drift means you faded, whether from a base that isn't deep enough yet, under-fuelling, heat, or simply going too long for your current fitness.
Used together, these two numbers are a proper aerobic dashboard. EF trending up across weeks says the engine is growing. Decoupling staying low says the engine is durable. That combination — more efficient and more durable — is exactly what a base phase is supposed to produce, and now you can see both.
What the shape should look like across a season
EF doesn't climb in a straight line, and knowing the normal shape stops you panicking at the wrong moment.
Through a base block, when most of your riding is easy aerobic work, EF on your benchmark ride should trend up steadily. This is the phase it's built for, and a rising line here is the confirmation that all that disciplined zone 2 riding is doing its job — the engine is growing. This is exactly where the ego struggles, because the rides feel too easy to be useful, and EF is the number that proves they aren't.
Through a hard build block, full of threshold and VO2 work, expect EF to plateau or even dip slightly. That's not a problem — you're carrying fatigue, your heart rate sits a little higher for a given power, and efficiency takes a temporary back seat to building top-end. After a recovery week, it should bounce back and ideally settle a notch higher than before. A dip during a hard block is normal; a dip that doesn't recover after rest is the one to question.
Heading into a peak, with fatigue clearing, you'd expect EF on a steady effort to be at or near its best for the season — the engine is both big and fresh. If your benchmark EF is strong and your aerobic decoupling is low going into an event, the foundation is exactly where you want it.
The mistake is reading a single block in isolation. A base-phase rise, a build-phase plateau and a peak-phase high are all good news. Learn the rhythm and you stop over-reacting to any one reading.
The honest caveat: heart rate is noisy
I won't oversell this, because EF has a real weakness, and it's the heart rate side of the equation. Heart rate is influenced by a long list of things that have nothing to do with fitness: heat, caffeine, poor sleep, stress, dehydration, illness, even a big meal. A single hot day can suppress the number; a stressful week can inflate it.
That's exactly why you track the trend on a controlled benchmark and never over-react to one ride. One low EF day means nothing — you slept badly, it was 30 degrees, you'd had three coffees. A string of declining EF readings on the same ride at the same perceived effort, with no obvious explanation, is a different matter. That's a signal worth acting on, and it usually shows up before your power drops. Sustained EF decline at steady RPE is one of the earliest fingerprints of accumulating fatigue or an oncoming illness. When I see it in a rider's data, it's a cue to look hard at recovery before the hole gets deeper.
This is also why EF sits so well next to the other things worth watching across a season — your HRV trend, your sleep, your training load on the PMC. No single metric is the truth. But EF earns its place because it's looking at something the others aren't: the quiet, slow growth of the aerobic base that all your harder work depends on.
How to use it this season
Keep it simple. Choose one benchmark aerobic ride you can repeat. Log it to TrainingPeaks, let the platform calculate EF and decoupling for you, and check the EF trend every few weeks rather than every ride. Through a base block, you want to see it climbing. Through a hard intensity block, expect it to plateau or even dip slightly as fatigue accumulates — that's normal, and it should recover after a rest week. Heading into an event, a strong EF trend plus low decoupling tells you the foundation is solid.
If you're a masters rider especially, this is one of the most motivating numbers you can track, because progress after 45 often hides from the FTP test. The threshold number can sit stubbornly flat while the engine underneath it quietly gets better and more durable. EF is how you see that. It's the difference between feeling like you're spinning your wheels and knowing the work is landing.
FTP gets the attention. But the riders who get properly fit are the ones who learn to read the number underneath it.
If you want the masters-specific take on this metric, the Efficiency Factor for masters cyclists piece goes deeper on why it matters after 45. For the wider dashboard, reading your training data covers the load metrics that sit alongside it. And if you want a coach reading these trends with you, we're on Skool.