Here's the issue with using FTP as your one progress metric. FTP captures your peak hour power. It does not capture how easily you're producing the rest of the work that fills your week. You can do an entire winter base block — eight or twelve weeks of disciplined zone 2 — and your FTP barely moves, because FTP isn't where the adaptation lives during that phase. Your aerobic engine has gotten significantly better. Your peak hour power hasn't.
That's the gap. And it's why a lot of masters cyclists who do the right work in base season come away frustrated. They've ridden carefully. They've been patient. The numbers haven't moved on the test the platform tells them is the test that matters. So they assume the training didn't work and reach for the harder sessions earlier than they should.
Efficiency Factor is the metric that closes that gap. It tells you whether the engine you're building is actually getting better, before the FTP test catches up. For masters cyclists, who need to invest more deliberately in base than they did in their twenties, EF is arguably the most useful single number you can track.
What Efficiency Factor Actually Is
Efficiency Factor — EF for short — is the ratio of normalised power to average heart rate on a steady aerobic ride. The formula is:
EF = Normalised Power (NP) / Average Heart Rate (HR)
So if you do a 90-minute zone 2 ride at an NP of 220 watts and an average heart rate of 140 bpm, your EF for that ride is 1.57.
The number on its own means little. EF varies between individuals based on resting heart rate, max heart rate, body composition, and a hundred other factors. What matters is your EF compared to your own EF on similar rides over weeks and months.
If your EF on the same kind of ride is rising, your aerobic engine is producing more power per heart beat — your fitness is improving even if FTP hasn't moved. If your EF is flat or falling, the work isn't producing the adaptation you'd expect, and something is off.
Joe Friel built EF into The Cyclist's Training Bible decades ago, and the metric has held up better than most of the alternatives. It's simple. It uses data you already have. And it captures something FTP doesn't.
How to Calculate It
You need a power meter or smart trainer and a heart rate strap (chest strap is far more reliable than wrist optical for this — wrist drift contaminates the reading). Then:
- Ride for at least 60 minutes at a steady aerobic intensity. Zone 2 or low tempo. No surges, no traffic stops, no group dynamics.
- Note normalised power for the ride.
- Note average heart rate for the ride.
- Divide NP by HR.
That's your EF for that ride. Log it in TrainingPeaks (which calculates it automatically anyway) or in your own spreadsheet. Repeat across rides of the same type. Watch the trend.
A few practical points:
- The ride needs to be steady for the number to be meaningful. A ride with hard climbs and easy valleys will give you an inflated NP relative to HR and produce a deceptively high EF.
- Indoor rides are best for repeatability — temperature, terrain, and effort are all controlled.
- Compare like with like. EF on a 60-minute steady ride is not directly comparable to EF on a 4-hour ride. Group your tests by duration and intensity.
- Heat and dehydration push HR up and EF down even with the same power. Note conditions in your log.
What the Trend Looks Like When It's Working
For a masters cyclist doing 8–12 weeks of disciplined zone 2 base work, the typical EF progression on a standard 90-minute ride looks something like:
- Week 0: 1.45
- Week 4: 1.51
- Week 8: 1.57
- Week 12: 1.62
That's a 12% rise across a base block. Same heart rate, more power. Same power, less heart rate. The aerobic engine is genuinely improving. The rider feels the change as easier-feeling rides at the same intensity, lower morning heart rate, and a longer durability before fatigue sets in.
Crucially, the FTP test at week 12 might not yet show the gain. The peak power capacity follows aerobic efficiency, often by a few weeks. If you only track FTP, you miss the underlying progress and get tempted to abandon the base block before it's finished delivering. EF gives you the early signal that the work is paying off.
What the Trend Looks Like When It's Not
The frustrating version. A masters cyclist does 8 weeks of careful base work, fully committed, and the EF graph looks like:
- Week 0: 1.50
- Week 4: 1.49
- Week 8: 1.51
- Week 12: 1.48
Flat. The aerobic engine isn't responding to the stimulus. This is the warning signal most riders ignore because their training plan tells them to keep going. EF says: something else is the limiter.
The usual suspects, in order:
- Sleep. Chronic short or low-quality sleep flattens EF more than almost anything else.
- Stress. Work and life stress elevate resting heart rate, lower variability, and trash recovery. EF flattens.
- Bloods. Iron deficiency, low vitamin D, low free testosterone — physiological limiters that no amount of training will override.
- Under-fuelling. Riding chronically low on carbs degrades adaptation quality. EF stalls.
- Wrong intensity distribution. "Zone 2" rides that are actually drifting into low tempo never produce the zone 2 adaptation. The grey-zone trap.
EF flagging is the early signal that one of these is the real problem. Without it, you'd push through another four weeks, hit your FTP test, see no movement, and wonder what you did wrong.
Why EF Matters More for Masters Cyclists
Three reasons.
The base block is more important. Masters cyclists generally need more aerobic depth than their younger selves to handle the same volume and intensity. A 30-year-old can ride threshold sessions on a thinner base and still adapt. A 50-year-old who tries the same is going to dig a hole. EF helps you confirm the base is doing its job before you build on top of it.
FTP movement is slower and quieter. The simple truth is that FTP gains slow with age. A 50-year-old who gains 10 watts of FTP in a year has done well. EF, in contrast, can move significantly across a base block even when FTP isn't budging — because aerobic efficiency improves through the same stimulus that builds peak power, just on a different timeline. EF gives masters cyclists a more sensitive progress metric.
The signal-to-noise ratio is worse. Sleep variability, hormonal shifts, illness frequency, life stress — all the noise that masks training adaptation tends to be louder for masters cyclists. EF, especially when smoothed across multiple rides, cuts through the noise better than spot tests.
How EF and Aerobic Decoupling Work Together
The two metrics answer different questions and they're at their best when used together.
EF asks: is my aerobic engine getting better over weeks and months? A long-arc metric. You compare today's EF to last month's EF on similar rides.
Aerobic decoupling asks: does my aerobic engine hold up over hours within a single ride? A within-ride durability check. You compare the first half to the second half of one ride.
A masters cyclist building toward a long sportive wants both to be good. Rising EF tells you the engine is improving in absolute terms. Low decoupling tells you the engine actually lasts the duration you'll need on event day. One number alone gives you half the picture.
Together, they give you the cleanest aerobic readout you can build without lab access. And they pair beautifully with home lactate testing, which sets the zones the EF and decoupling tests run inside.
Setting It Up in TrainingPeaks
If you're using TrainingPeaks — which most serious masters cyclists end up doing — you don't have to calculate EF by hand. The platform does it automatically on every ride that has both power and heart rate data.
Three things to do:
- Add the EF field to your dashboard. Settings → Customize → drag the metric in.
- Tag your steady zone 2 rides as a specific workout type (e.g. "Endurance — steady"). This lets you filter and graph EF over time on a like-for-like basis.
- Once a month, look at the chart. Trend up across base, plateau across build, slight drift down across peak race blocks (because heart rate suppression begins to kick in). That's the healthy pattern.
Some platforms outside TrainingPeaks also calculate EF, but TrainingPeaks has been the most reliable for this metric specifically. If you're already a paid subscriber, this is one of the things you're paying for.
Common Mistakes
A few things that mess up EF as a useful metric:
Comparing rides that aren't comparable. Indoor vs outdoor, hilly vs flat, hot vs cold, fresh vs fatigued — all materially affect EF. Segment your data and compare like to like.
Over-reading single rides. EF on any one ride is noisy. The trend across 4–6 rides is the signal. Don't change your plan based on a single bad reading.
Using a wrist HR sensor. Wrist optical drift on rides longer than 60 minutes is a known issue. EF needs reliable HR. Use a chest strap.
Ignoring rest day patterns. Resting heart rate drifts up under fatigue, illness, or stress. If your morning RHR has crept up and your training EF has dropped, that's signal — not a reason to retest.
Pushing through despite the signal. This is the worst one. EF flattens for four weeks; rider says "next week it'll move"; doesn't move; rider digs a deeper hole. EF is information. Listen to it.
A Practical Plan for Using EF
If you're starting from zero with this metric, here's a sensible approach:
- Set a benchmark. Pick one steady 60–90 minute zone 2 ride profile you can repeat. Indoor trainer is easiest. Same warm-up, same target power, same conditions.
- Run it three times in two weeks. Average the EF. That's your starting baseline.
- Run it again every two weeks during your base block. Same conditions. Log the EF.
- Look at the trend across 8–12 weeks. Rising? You're adapting. Flat? Investigate.
This is the kind of unglamorous, data-led process that separates serious masters cyclists from cyclists who just count hours. The pros do this. The athletes Dan Lorang programmes for do this. There's no reason a self-coached amateur with a power meter and a chest strap can't.
Where This Sits in the Plateau Conversation
EF is one of the cleanest tools for figuring out whether you've actually plateaued or whether you're mid-progress and just can't see it on the FTP graph yet. The pattern matters:
- EF rising, FTP flat. You're improving. Stay the course. The FTP gain will follow.
- EF flat, FTP flat. Real plateau. Investigate the limiters.
- EF falling, FTP flat or falling. Something is wrong. Sleep, bloods, fuelling, stress — find it before you change the training.
Most plateaued masters cyclists assume they're in case three when they're actually in case one. The training is working, the tracking just isn't catching it yet. EF makes that distinction visible.
If you've stalled and you can't tell whether the issue is training, fuelling, recovery, or something else underneath, the Plateau Diagnostic walks through the four-question audit that points you at the actual limiter. Four minutes, free.
Where to Go From Here
Once you're tracking EF, the natural next step is using it to inform your weekly planning. Rising EF means the base block is working — keep building duration and consistency, then layer intensity on top. Flat EF means investigate before adding work. Falling EF means rest, recover, find the underlying issue.
For more on building the engine that drives EF up, the zone 2 training complete guide is the foundational read. The polarised training guide covers the full weekly model. And aerobic decoupling for cyclists is the within-ride companion metric you should be tracking alongside EF.
For masters cyclists specifically, the masters cyclist guide to getting faster after 40 puts the metrics in the bigger picture of training in your forties and fifties. EF is one piece of that puzzle. It's also the piece most riders never use.
Set the metric up in TrainingPeaks this week. Run a baseline ride. Run another in two weeks. Compare. The data starts working for you immediately, and the trend across the next base block tells you whether the work is doing its job — long before the FTP test gives you an answer either way.