What Is Efficiency Factor in Cycling and How to Improve It

James. You're tuned in to the WattPlan Podcast, and I'm James. Family life, a day job, the odd podium, building WattPlan, and a habit of reading sports science long after I should be asleep. This week, a number that can tell you you're fitter even when your power hasn't budged. Same watts, lower heart rate. So what is Efficiency Factor, and how do you actually get it to go up? Lyra's our AI research voice, and every study is linked in the show notes.

Lyra. It's your Weighted Power divided by your average heart rate, so roughly watts per heartbeat. If it rises over weeks on the same kind of ride, your heart is doing less work for the same power, and that's aerobic fitness seen from the inside. The way to raise it is consistent aerobic riding, and patience.

James. Give me an actual number, because 'watts per heartbeat' sounds like something off a cereal box.

Lyra. Fair. Say a ride at 220 watts of Weighted Power, with your heart averaging 145. That's an Efficiency Factor of about one and a half. A month later, the same 220 watts at 138 beats a minute nudges it up to nearly 1.6. Same output, less effort from the heart.

James. And what's changed inside, for that to happen?

Lyra. Broadly three things. Your heart pushes more blood per beat, there are more capillaries around the muscle fibres to deliver oxygen, and the mitochondria use it better. None of that needs your power to go up before it shows, which is why this number can pick it up.

James. But heart rate's so twitchy. Coffee, sleep, a warm room. Surely it's too noisy to tell you anything?

Lyra. It's noisy ride to ride, you're right, and that's the honest weakness. And both studies we looked at this week are really about heart rate misbehaving. The first is a 2001 review in Exercise and Sport Sciences Reviews by Edward Coyle and a co-author, on cardiovascular drift. During long exercise, the blood your heart pushes per beat slowly falls after ten to twenty minutes, mainly because heart rate keeps rising. [2]

James. So the longer the ride, the worse my number looks.

Lyra. On the same ride, later on, yes. Which means you can't compare a two hour ride with a forty minute one and call it a trend. Like with like. And the first ten to fifteen minutes of any ride can mislead too, while your heart rate settles.

James. So the start of the ride's no good, the end of a long ride's no good. What's left?

Lyra. The steady middle of a steady ride, repeated. That's the bit to compare. A long ride on a hot afternoon will always look worse than an hour on the turbo with a fan, and neither is wrong. They just aren't the same test. Pick one ride you can repeat, and let that be your measure.

James. And the second study?

Lyra. The one I'd want every self-coached rider to know. It's a study in the Journal of Applied Physiology by Yann Le Meur and colleagues. Twenty four highly trained triathletes, split into an overload group and a normal training group for three weeks. Eleven of them ended up overreached, tired with their performance down. Changes in heart rate, along with blood lactate, were the two measures that best picked them out. [1]

James. Okay, so how does that connect to my number going up?

Lyra. Because heart rate moves with fatigue as well as fitness. The article's point is that deep fatigue can hold your heart rate down, and that flatters Efficiency Factor. So a sudden jump after a brutal block isn't always good news. If it rises while you feel wrecked and your legs won't do the efforts, read it as fatigue, not fitness.

James. That's sneaky. A good number for a bad reason.

Lyra. Exactly. It's why you never read it on its own. How you feel, and whether the sessions are going well, are part of the picture.

James. Can I compare mine with my mates', though? If mine's higher, I'm fitter, surely?

Lyra. No, I'd steer you off that one. It depends heavily on your own heart rate range, so a rider whose heart naturally runs high gets a lower number for the same fitness. Your trend is what matters. Someone who goes from 1.25 to 1.4 over a season has made excellent progress, whatever anyone else's says.

James. Does WattPlan do the like for like bit for you?

Lyra. In the background, yes. It sorts your rides by Intensity into endurance, sweet spot, threshold and VO2max, leaves recovery rides out, and tracks each group over ninety days. When a ride comes in at least 5 percent above its group's average, once that group has four or more rides, you get a note that your efficiency is improving. The Coach sees those trends too.

James. And the chart on the Progress page? Is that by zone as well?

Lyra. No, that one's a weekly average across every ride with power and heart rate, easy and hard together. So read it over months, not weeks. The like for like comparison is the one behind those notes.

James. So what should the number do through a season?

Lyra. In a base block, expect gradual rises, because steady riding builds exactly what it measures. In build, as intensity and fatigue go up, it may flatten or dip slightly, and that's normal. In a taper it often holds or rises as fatigue clears, though a fresher heart can also beat a little faster for the same power.

James. If you're new to this, should you even be looking at it?

Lyra. Glance at it, don't chase it. If you're new to structured training, ride consistently and mostly easy, and the number takes care of itself. Meaningful changes take four to eight weeks of steady training to show, so a flat month early on isn't a failure.

James. And for people who train with power and live in the data?

Lyra. If you train with power, clean up your inputs. A chest strap rather than a wrist sensor, because wrist readings can lag and spike. Indoors gives the most controlled comparison. And a ride that syncs as a summary without its second by second file may be using average power rather than Weighted Power, which reads a little lower on a variable ride.

James. And if you race?

Lyra. If you race, watch the number on your sweet spot and threshold rides, because that's how cheaply you're producing race-like power. Rising there going into an event is a good sign. Just remember the taper caveat, a fresh heart can run a little faster.

James. And Fitness? Doesn't that already tell me I'm getting fitter?

Lyra. It tells you how much training you've done. Efficiency Factor tells you how your body is responding to it. You can have a high Fitness and a flat Efficiency Factor if the training isn't producing adaptations. That's why the two are worth reading side by side.

James. Where does the evidence run out?

Lyra. Neither study tested Efficiency Factor itself. One is about why heart rate drifts in long exercise, the other about spotting overreaching in a small group of triathletes over three weeks. Nobody has shown how much a typical amateur's number should rise in a season. So it's a sensible measure built on sound physiology, not a validated test.

James. Practical, then. What does someone do with this tomorrow?

Lyra. Pick one repeatable ride, a steady endurance hour on the same route or the turbo, chest strap on, once a week. At the end of each month, look at Efficiency factor in the Metric explorer on the Progress page for the long view, and ask the Coach how your endurance rides are trending, because it sees them grouped. If the number jumps while you feel flat, ask about an easier week.

James. So, same ride, same conditions, read it monthly, and if it suddenly looks brilliant while I feel terrible, that's fatigue lying to me.

Lyra. Aerobic fitness is the same watts for fewer heartbeats, and it's earned slowly. Ride steady, give it the weeks, and believe the trend over the single ride.

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.