CoachingAnswer

HOW DO I DO THRESHOLD INTERVALS?

By Anthony WalshRoadman CyclingUpdated 26 May 2026

WHO THIS IS FOR

IS THIS YOU?

The rider starting structured interval training

You want the single highest-impact interval format for raising FTP without an overcomplicated programme.

The rider whose threshold sessions feel inconsistent

You know you should be doing them but you blow up, die in the second interval, and never quite hit the target numbers.

THE ROADMAN VIEW

The 2×20 is the most discussed interval in amateur cycling and also the most butchered. Anthony has done it with World Tour coaches and club cyclists and the execution gap is staggering. The pros treat it like a controlled effort — precise pacing, good fuelling, the same tempo from minute one to minute twenty. The amateurs go out at 110%, suffer through the first twenty, barely survive the second, and check the session off as done while wondering why their FTP isn't moving.

The insight from Joe Friel, which he has repeated across multiple podcast formats, is that threshold work is about total time at quality intensity, not heroics. A 100% FTP effort you hold for the full 20 minutes is more valuable than a 110% effort that collapses to 85% at minute twelve. The adaptation happens in the steady accumulation of time at threshold — you cannot accumulate it if you're dying.

The other piece that gets missed is fuelling. Stephen Barrett, World Tour coach at AG2R, points out that amateurs often do threshold intervals fasted or under-fuelled because they don't feel hungry beforehand. Hard threshold work burns predominantly carbohydrate. Go in glycogen-depleted and you are doing a completely different physiological session to the one you intended.

EXPERT EVIDENCE

WHAT THE EXPERTS SAY

Joe FrielAuthor of The Cyclist's Training Bible; co-founder of TrainingPeaks
Threshold intervals are the most reliable FTP-building session for trained amateurs, but their value depends almost entirely on honest pacing. Time at quality intensity matters more than peak effort — a conservative start that allows a consistent, strong finish is physiologically superior to a hard start that collapses.
Hear it: Joe Friel's Cycling Training Plan Structure | Roadman Cycling
Stephen BarrettHead coach, Decathlon AG2R La Mondiale (UCI WorldTour)
Threshold sessions at World Tour level are fuelled and prepared for like races. Nutrition before and during is not optional — the quality of the adaptation depends on having adequate glycogen to sustain the effort at the target intensity.
Hear it: World Tour Cycling Coach on What FTP Misses | Roadman Cycling

PRACTICAL APPLICATION

DO THIS WEEK

Start at 95% FTP for the first 5 minutes
Deliberately hold back in the first five minutes of each interval. Your RPE will feel easy — that's correct. By minute fifteen you'll be working hard. Starting at 110% guarantees a fade. Starting at 95% allows a build.
Fuel the session: 40–60g of carbs in the hour before
A bowl of porridge, some toast with jam, or a carb drink 45–60 minutes before the session. Threshold sessions burn carbohydrate at high rates — going in under-fuelled means the effort is unsustainable at the target power.
Build from 2×15 to 2×25 over 6 weeks
If 2×20 is too challenging initially, start with 2×15 min at 95% FTP. Add 2–3 minutes to each interval every two weeks. Reaching 2×25 min is a genuine threshold block completion target.

COMMON MISTAKES

WHAT CYCLISTS GET WRONG

MISTAKEStarting the first interval at 110%+ FTP because it feels sustainable initially.
FIXPacing threshold work is a skill. Start deliberately under your target and build. Check your numbers at 5 minutes and adjust — don't wait until you're blowing up.
MISTAKEDoing threshold sessions on consecutive days.
FIXAt least one full easy day between threshold sessions. Most amateurs need two. Stacking quality work without recovery produces under-adapted training at best, overreaching at worst.
MISTAKEDoing threshold work fasted or with minimal carbohydrate.
FIXFuel 45–60 minutes before with 40–60g of carbs. This is not about weight management — it is about executing the quality session you intended.

FAQ

FREQUENTLY ASKED QUESTIONS

Should I do threshold intervals indoors or outdoors?

Indoors is ideal for precision — no traffic, no descents, consistent ERG mode power. Outdoors works if you have a long steady climb or a quiet flat road. The environment matters less than consistent pacing.

How many threshold sessions should I do per week?

One per week is the baseline for most amateurs. Two is possible in a dedicated build block if the rest of your week is easy and you are fuelling and sleeping properly. Three or more quickly leads to overreaching.

What is the difference between 2×20 and 3×15 threshold intervals?

Both produce roughly the same time at threshold (40–45 minutes). The 3×15 format gives slightly more rest so is more accessible when you are new to threshold work. The 2×20 is the classic format because 20 continuous minutes drives meaningful lactate clearance adaptation.

Can I do threshold intervals without a power meter?

Yes — use heart rate (roughly 90–95% of max HR) or RPE (7–8 out of 10, where you can speak two or three words but not hold a conversation). Power is more precise, but HR and RPE produce effective threshold sessions without it.

What should I eat after a threshold session?

30–60g of fast carbs plus 20–30g of protein within 45 minutes post-session. A recovery drink, a bowl of rice with chicken, or Greek yoghurt and banana all work. This recovery window is where the session's adaptation is consolidated.

RELATED EPISODES

HEAR THE CONVERSATIONS

Joe Friel's Cycling Training Plan Structure | Roadman Cycling

World Tour Cycling Coach on What FTP Misses | Roadman Cycling

Heat Training for Cyclists: +30 Watts FTP | Roadman Cycling