Threshold Intervals for Cycling, From 2x20 to Over-Unders

James. This is the WattPlan Podcast and I'm James. I juggle a family, a job and WattPlan, sneak the occasional podium, and read sports science on the sofa when I should be asleep. Today it's the session every club rider knows, the 2x20 at threshold. Is it really the gold standard, and are over-unders any better? Lyra, our AI research voice, has the studies, and they're all linked in the show notes.

Lyra. Threshold intervals work, but ridden at full FTP they're harder than most people think, and on their own they aren't the quickest way to get fitter. Start them a touch under FTP, and ride them alongside some harder work above threshold, not instead of it.

James. A touch under? The whole point of FTP is that you can hold it for an hour.

Lyra. That's the definition, and it's where the trouble starts. Borszcz and colleagues, in the International Journal of Sports Medicine in 2018, took 23 trained men, worked out their FTP from a 20 minute test, then had them ride at that power until they couldn't. On average they lasted about 51 minutes, not 60. And the spread was wide, so plenty of them were done well before that. [1]

James. So a 2x20 at full FTP is forty minutes at a power some of them could only hold for forty-odd minutes in one go.

Lyra. For some riders, yes. The rest between blocks helps, but it explains why the second twenty so often unravels. And there's a second study that points the same way. Inglis and colleagues, in the International Journal of Sports Physiology and Performance in 2020, found the highest power where blood lactate stays steady. On average it sat at about 93 percent of FTP. [3]

James. Hang about. So the line I think I'm riding on is actually a bit above the line that matters?

Lyra. For the average rider in that study, yes. Below that steady state you can keep going for a long time. Above it, lactate keeps climbing until you slow down. So a block at 100 percent sits above it for a lot of people. WattPlan's threshold sessions are written at FTP, and if the last block keeps falling apart, turn the intensity down a notch in the player and see if you can finish it.

James. Why the difference between riders, though? Same test, same percentage, and one lad's fine while the other's in bits.

Lyra. Because FTP is an estimate, and it fits some people better than others. Ninety-five percent of your best twenty minutes is a rule of thumb. A rider with a big sprint and a short fuse can post a strong twenty minutes that they could never stretch to an hour. A diesel who's slow to get going might post a modest twenty and hold it for ages. Same formula, very different riders underneath it.

James. So two people at 100 percent of FTP aren't really doing the same session.

Lyra. Not quite, no. That's the most useful thing to take from those studies. The percentage on the screen is a starting point, and your body tells you the rest. If the last block falls apart every week, the target's too high for you, whatever the test said. If you finish a 2x20 feeling you could do a third, it might be time to retest.

James. But surely if it hurts more, it works better? That's half of cycling culture right there.

Lyra. It's a fair instinct, and the best trial on interval length says otherwise. Seiler and colleagues, in the Scandinavian Journal of Medicine and Science in Sports in 2013, split recreational cyclists into groups of about nine for seven weeks. One group did four efforts of sixteen minutes, close to threshold. Another did four of eight minutes, harder. [4]

James. And the long ones won, because more time at threshold.

Lyra. The opposite. The eight minute group improved about twice as much. The sixteen minute group did no better than four short four minute efforts, and only a little better than a group that just rode easy. Long threshold work helped. It just wasn't the biggest lever.

James. Okay, that's a bit deflating. So should I bin the 2x20?

Lyra. No. It's still a brilliant session for learning to hold a steady, hard effort, and that's exactly what a time trial or a long climb asks of you. The point is what goes around it. In the trials that compared threshold-only weeks with weeks that included harder work above threshold, the harder work moved fitness further. So threshold earns its place next to a VO2max session, not as the whole week.

James. Right. And over-unders. Every group ride I've ever done is basically an over-under. Are they better than steady blocks?

Lyra. Honestly, nobody knows. We searched the research for a trial comparing over-unders with steady threshold work and couldn't find one. The usual story is that the over pushes lactate up and the under teaches you to clear it while you're still working hard. That's plausible, and it matches racing, but it hasn't been measured.

James. So they're a coach's hunch.

Lyra. A sensible hunch, built on experience, which isn't nothing. I'd treat them as race practice rather than a cleverer route to a higher FTP. The plan doesn't save them for race season, so if you want more of them close to an event, that's your call.

James. Let's make it real for people. If you're new to this, and threshold just sounds like a word for suffering?

Lyra. If you're new to this, you don't need threshold blocks yet. Build the habit first, with mostly easy riding and one steadier session a week, the kind where talking gets hard but you're not gasping. That's how WattPlan plans it for beginners too. A beginner plan stays on sweet spot all the way through.

James. And if you train with power?

Lyra. If you train with power, the plan leans towards shorter threshold sessions early on and longer ones, like two twenties or three fifteens, as the weeks go by. Let the last block tell you whether the number's right. Your own last-rep power is a better guide than any percentage on a screen.

James. And for the racers? The ones who'll ignore all this and do 2x20 at 105 percent.

Lyra. Those riders. If you race, the build is where threshold earns its keep, paired with a VO2max day and an easier day between them. Tell the plan you're training for a time trial and threshold comes round more often. And the race simulation session, with its surges above threshold, is the closest thing in the library to the real thing.

James. And what does WattPlan actually give you here?

Lyra. The library has a good spread of threshold sessions, from a short express one to a two hour four by twenty, plus steps, a progressive build, a race simulation and an over-under. On a smart trainer the player holds the target for you, so you're not chasing the number.

James. And when does it put them in a plan?

Lyra. Once the build phase starts, alongside sweet spot and VO2max work, and more often if you've told it you're training for a time trial. Base phases and beginners stay on sweet spot.

James. What can't the research tell us yet?

Lyra. Quite a bit. These trials are small, mostly men, and nobody can be blinded to the session they're riding. No trial has put over-unders against steady blocks. And how closely your own FTP matches your own steady state can only be checked with a blood lactate test, which most of us will never do. So the effort in your last rep matters more than the percentage.

James. So this week. Stop treating the 2x20 as a test, turn it down a notch if the second one falls apart, and keep the VO2max day in.

Lyra. Yes. Ride the first twenty like you could do a third. The threshold session that makes you faster is the one you can repeat next week, a little longer.

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.