The WattPlan Podcast · Episode 40 · 9 min
Nine numbers, one question: am I getting fitter?
Next episodes: Is your Efficiency Factor going up? · What is cardiac decoupling telling you? · What is Load actually measuring?
Read the transcript
James. Hello, and welcome to the WattPlan Podcast. I'm James. Family, work, the odd podium, and WattPlan being built around all three, with more sports science papers on my desk than any one person should own. This week it's the wall of numbers. Load, efficiency, decoupling, MAP, a VO2max estimate. Which of them actually tell me I'm getting fitter, and which ones can I stop staring at? Lyra's here, our AI research voice, and the studies are linked in the show notes.
Lyra. None of them on its own, honestly. Each answers a different question. Load and hours say how much you did. Intensity says how hard. Efficiency and decoupling say how your heart is coping with the work. MAP and the VO2max estimate track your ceiling. Fitness shows up when two or three of those move the right way together, over weeks.
James. Start with Load, then. I look at it every day and I'm not sure I could define it.
Lyra. It's the training stress of a ride, built from how hard and how long. An hour flat out at your FTP is 100. Your Fitness is a long running average of it, about six weeks, and Fatigue a one week average. So weekly Load is the input to almost everything else.
James. And Intensity is just how hard it felt?
Lyra. Not how it felt, how it measured. It's your Weighted Power as a share of your FTP. An endurance ride sits below about 75 percent. Threshold is around 95 to 105. It's most useful as a check. If an easy day keeps coming out at 85, it wasn't easy.
James. Guilty. And hours? That one feels too obvious to bother with.
Lyra. Which is exactly why people skip it. Endurance adaptations need time on the bike, and there's no shortcut. Through a base period, steady hours matter more than how hard any single ride was.
James. Okay, average power and average heart rate. They feel like the boring ones.
Lyra. On their own, they are. A ride full of surges and coasting can average the same power as a steady one and cost far more. And heart rate moves with heat, caffeine, sleep and stress, not just effort. They get interesting when you divide one by the other.
James. Which is efficiency factor.
Lyra. Right. Weighted Power divided by average heart rate, so roughly watts per heartbeat. If it climbs over a couple of months on the same kind of ride, your aerobic engine is improving. The trick is comparing like with like. An endurance ride against endurance rides, not against a race.
James. And decoupling. Mine went red last week and I assumed I'd lost all my fitness overnight.
Lyra. You almost certainly hadn't. Decoupling compares power per heartbeat in the first half of a steady ride with the second. If heart rate drifts up for the same power, that's decoupling. Under five percent is a well developed aerobic base, over ten is a lot of drift. But one hot day or one tired ride will push it up.
James. So how should I be reading it?
Lyra. As a pattern. In WattPlan it's the one metric shown ride by ride rather than by week, and only steady rides of an hour or more count, after setting aside the warm-up and cool-down. Interval sessions would measure the workout, not you. Watch whether the typical number drifts down over a season.
James. Now the one I really want. How can an app possibly know my VO2max?
Lyra. It can't measure it. It estimates it. MAP is your best five minute power each week, and the estimate takes that per kilo of body weight and runs it through a standard cycling equation from the American College of Sports Medicine. The reason power can stand in for oxygen at all comes from the first of two studies we looked at.
James. Go on.
Lyra. Hawley and Noakes, in the European Journal of Applied Physiology in 1992. They tested a hundred trained cyclists, men and women, to exhaustion in the lab. Peak power predicted VO2max very closely, explaining 94 percent of the variation between riders. [1]
James. Did it predict anything on the road, or just in the lab?
Lyra. They checked that too, in a smaller group of nineteen riders. Peak power also predicted their 20 kilometre time trial times well. So it wasn't just one lab number tracking another. It lined up with how fast they actually went.
James. Ninety four percent. So the estimate's basically as good as a lab test.
Lyra. Not quite, and that's an easy leap to make. Their peak power came from a lab test to exhaustion, not your best five minutes on the road in a given week. So the app's version borrows the idea rather than copying it. And the estimate is really your power per kilo dressed up as oxygen.
James. But surely if my VO2max estimate goes up, my actual VO2max went up? Isn't that the whole point of it?
Lyra. Not necessarily. It rises if your five minute power rises, or if your weight drops, even if your lab VO2max hasn't moved at all. So read it as a fitness trend that mixes aerobic power and body weight. If it stalls while MAP keeps climbing, the scales have probably moved.
James. Can you even train VO2max? I've always heard it's mostly in your genes.
Lyra. The second study is a nice answer to that. A 2013 meta-analysis in PLoS ONE by Bacon and colleagues pooled 37 studies of healthy people who were sedentary or only recreationally active. Six to thirteen weeks of interval training raised VO2max by about half a litre of oxygen a minute on average. With longer intervals, everyone responded. [2]
James. Everyone. So the non-responder story is a myth?
Lyra. In those people and those programmes, nobody failed to respond to longer intervals. But they started untrained. Someone who's ridden for years has less room left, so for you the trend in MAP matters more than any single number.
James. Right. If someone's new to this and opens that page for the first time, which one or two numbers should they look at?
Lyra. If you're new to structured training, just weekly Load and hours. Are you riding consistently, and is the line creeping up gently rather than lurching? The other seven get more useful after a few months of rides.
James. And if you train with power and wear a heart rate strap?
Lyra. Add efficiency and decoupling, and wear the strap on your steady rides, because both depend on it. Then read pairs. Load up and efficiency up, you're absorbing the work. Load up and efficiency sliding for several weeks, fatigue may be outrunning adaptation, which is worth raising with the Coach.
James. And if you're racing or chasing a target, which one matters most?
Lyra. MAP, probably. It's your ceiling, and FTP has limited room to grow under it. If you're racing, watch it through blocks of VO2max work. A rising MAP with a flat FTP usually means the ceiling's lifting and the threshold work still has room to pull FTP up behind it.
James. Where does all this run out?
Lyra. The VO2max estimate leans on a lab relationship from trained riders, applied to road efforts it was never tested on. The interval meta-analysis was in untrained people under 45. And none of these metrics has been tested as a way of steering an amateur's training week to week. They're signals to read together, not verdicts.
James. So what do I actually do this week?
Lyra. Two things. On Progress, open the Metric explorer, set it to six months, look at weekly Load, then switch to Efficiency factor and compare the two. Then pick one steady ride this week, an hour or more with a heart rate strap, so decoupling has something honest to measure.
James. So, stop panicking at single red bars, read numbers in pairs, and treat my VO2max as a trend with my bathroom scales built in.
Lyra. And when you look at any of them, ask what it's being compared with. The same kind of ride, over enough weeks, tells you something. One number, on one day, mostly tells you about that day.
Lyra. The full article and every study we mentioned are on the WattPlan blog, linked in the show notes. And if you've enjoyed this, follow the WattPlan Podcast wherever you're listening, so you don't miss the next one.
James. And if you want a plan built around the time you've actually got, get WattPlan on the App Store or Google Play. Thanks for listening.
Voices produced with ElevenLabs. James's voice is a clone of his own, Lyra is an AI voice, and James reviews every episode.
Numbers without context are just noise. The Metric Explorer puts nine key training metrics on trend charts, week by week and, for decoupling, ride by ride, so you can see where your fitness is heading, not just where it was on one ride.
This is what each metric tells you, why it matters and how to use it.
Training Load
What it measures. The total stress of a workout, combining intensity and duration into a single number.
The formula. Load = Intensity² × hours × 100
A one-hour ride at your FTP produces a Load of 100. An easy two-hour spin might produce 80. A hard 90-minute threshold session might hit 120.
How to use it. Track weekly Load totals to manage training volume. A sudden spike in weekly Load without adequate recovery can leave you carrying too much fatigue. Aim for gradual increases during build phases.
Intensity
What it measures. How hard a ride was relative to your FTP.
The formula. Intensity = Weighted Power / FTP
An Intensity of 0.75, shown as 75% in the explorer, is a solid endurance ride. An Intensity of 1.0 means you rode at threshold for the entire session. Above 1.05 indicates VO2max territory, sustainable for only short efforts.
How to use it. The value tells you whether you're hitting the right intensity for each workout type. If your plan prescribes an endurance ride but your Intensity is 0.85, you're riding too hard. Compare similar workouts to see whether the same intensity is becoming easier over time.
Average Power
What it measures. The simple mean of all power readings during a ride.
Unlike Weighted Power, average power doesn't account for variability. A ride with big surges and coasting can have the same average power as a perfectly steady effort, but the physiological cost is very different.
How to use it. Best for steady-state efforts like time trials, indoor trainer sessions and long endurance rides where power is consistent. For variable outdoor rides, Weighted Power is more meaningful.
Average Heart Rate
What it measures. Mean heart rate across the ride.
Heart rate responds to far more than just effort. Heat, caffeine, fatigue, stress and hydration all move the needle. That sensitivity is both its limitation and its strength.
How to use it. Track average HR for the same workout types over time. If your average HR drops while power stays constant, your cardiovascular system is adapting. Pair it with power data via Efficiency Factor for the clearest picture.
Duration
What it measures. Total ride time, shown as hours per week.
How to use it. Monitor weekly duration to ensure your volume matches your training plan targets. Endurance adaptations require time on the bike. There are no shortcuts. During base phases, duration matters more than intensity.
Efficiency Factor (EF)
What it measures. How many watts you produce per heartbeat.
The formula. Efficiency = Weighted Power / Average Heart Rate
A higher EF means your cardiovascular system is delivering more power with less cardiac effort. This is one of the most sensitive indicators of aerobic fitness improvement.
How to use it. Compare EF within the same intensity zone over 4-8 week blocks. A rising EF in your endurance zone means your base training is working. EF improvements during sweet spot indicate your sustainable power is increasing.
Read more in What Is Efficiency Factor in Cycling.
Cardiac Decoupling
What it measures. How much your heart rate drifts relative to power during a ride.
The formula. Compares the power-to-heart-rate ratio in the first half of a ride with the second half. The explorer scores only steady rides of an hour or more with both power and heart rate, after setting aside a 10-minute warm-up and a 5-minute cool-down, and shows one bar per ride.
A decoupling of 3% means your heart rate barely rose, a sign of excellent aerobic fitness. Above 10% means your HR drifted significantly, indicating your aerobic system couldn't sustain the effort.
How to use it. The colour coding makes this one simple.
- Green (below 5%). Well-trained aerobic base. Your cardiovascular system handles this intensity comfortably.
- Amber (5-10%). Developing. Your base is building but not yet fully adapted.
- Red (above 10%). Significant drift. This intensity exceeds your current aerobic capacity.
Read more in What Is Cardiac Decoupling in Cycling.
MAP (Maximal Aerobic Power)
What it measures. Your best 5-minute power, a proxy for the maximum power you can produce at VO2max.
MAP is the ceiling of your aerobic engine. Every other metric, FTP, endurance power and race pace, is constrained by how high your MAP sits.
How to use it. MAP is directly trainable through VO2max intervals, 3-5 minute efforts at 106-120% of FTP. Track weekly MAP in the explorer to see whether your high-intensity work is raising the ceiling. A rising MAP means your FTP has room to grow.
Typical values.
| Rider Level | MAP (W/kg) |
|---|---|
| Recreational | 3.0-4.0 |
| Trained amateur | 4.0-5.0 |
| Competitive | 5.0-6.0 |
| Elite | 6.0+ |
Estimated VO2max
What it measures. An estimate of your maximum oxygen consumption, derived from your best 5-minute power and body weight.
The formula. VO2max = (10.8 × MAP / weight) + 7, the American College of Sports Medicine cycling equation
It works because peak power is a close predictor of VO2max in trained cyclists, as Hawley and Noakes showed in 1992.
An important distinction. True VO2max, measured in a lab with a gas analyser, has a strong genetic component and is only modestly trainable, with training studies averaging gains of roughly 15 to 20% and wide individual differences. This estimate is different. It rises with training because it tracks power output, which improves through better pedalling economy, neuromuscular efficiency and lactate tolerance, even when your actual oxygen uptake stays the same.
Treat this number as a fitness indicator that combines your aerobic power with your body composition, not as a lab measurement.
How to use it. Watch the trend rather than fixating on absolute values. A rising estimated VO2max confirms that your training is producing results. If it plateaus while your MAP is still rising, it may indicate a change in body weight.
Typical ranges (ml/kg/min).
| Level | Male | Female |
|---|---|---|
| Recreational | 35-45 | 30-40 |
| Trained | 50-60 | 45-55 |
| Competitive | 60-70 | 55-65 |
| Elite | 75-85 | 65-75 |
Which Cycling Metrics Should I Watch Together?
No single metric tells the full story. The value of the Metric Explorer is seeing how these numbers move together over time.
- Rising Load + rising Efficiency = productive training block. You're absorbing the load and adapting.
- Rising Load + falling Efficiency = accumulating fatigue without adaptation. Time for a recovery week.
- Stable power + falling HR = aerobic improvement. Your engine is getting more efficient.
- Rising MAP + stable FTP = your ceiling is lifting. FTP gains often follow with threshold work.
- Falling decoupling + rising EF = your aerobic base is strengthening. Long rides are having an effect.
How Often Should I Check the Metric Explorer?
The Metric Explorer groups most metrics by week, smoothing out the noise of individual rides to show the trends that actually matter. Check in once a week to confirm your training is moving in the right direction.
Sources
- Peak power output predicts maximal oxygen uptake and performance time in trained cyclists, European Journal of Applied Physiology and Occupational Physiology
- VO2max Trainability and High Intensity Interval Training in Humans: A Meta-Analysis, PLoS ONE