CyclingVO2maxIntermediate 64 min

40/20 VO₂max intervals on the bike (3 × 10 min)

40/20 intervals: three 10-minute blocks alternating 40 seconds at 115–125% of FTP and 20 seconds easy, with 5 minutes' recovery between blocks. 20 minutes of work in a 64-minute session. For intermediate to advanced riders working on VO₂max.

Written by Pierre Halloo · Updated 25 October 2026

Session profile63 blocks

At a glance

Duration: 64 min
Main target: 115–125%FTP5 Z5 · VO2 Max
Time at target: 20 min
Estimated load: 70
Structure: 3 × (10 × 40″ at 115–125% FTP, 20″ recovery), 5′ between sets
Level: Intermediate
Equipment: Power meter · Smart trainer

The session in detail

FTP

Time in zone

Z134 min
Z210 min
Z520 min

What the targets mean

The session's targets, in watts for three reference FTPs
Target	Zone	Time	FTP 200 W	FTP 250 W	FTP 300 W
115–125%	5VO2 Max	20 min	230–250 W	288–313 W	345–375 W
50–60%	1Recovery	9 min	100–120 W	125–150 W	150–180 W
45–55%	1Recovery	15 min	90–110 W	113–138 W	135–165 W

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What this session is for

The 40/20 keeps the same work-to-rest ratio as the 30/15, two to one, but stretches each piece. Twenty seconds of recovery is too short for your oxygen uptake to drop: over a 10-minute block, it stays close to its maximum. The slightly longer 40-second efforts are ridden a notch lower.

It's a very common format among coaches and on training platforms, but its origin hasn't been traced and no study has tested it as such. It rests on the same logic as studied short intervals like Rønnestad's 30/15, which remains the better-documented choice.

Who it's for

Intermediate to advanced riders with a recent FTP and a few short-interval sessions behind them, such as 30/30s. Handy if surges every 30 seconds break your rhythm: here, each effort lasts long enough to settle into.

When to do it

One or two VO₂max sessions a week at most, with an easy day between hard sessions and none the day before a race. To ease in, start with 8-minute blocks, then go to 10; after that, add a fourth block. You can swap it from block to block with the 30/15.

How to do it

Warm-up
15 min
5′ at 45–55% FTP + 5′ at 56–65% FTP + 5′ at 66–75% FTP
15 minutes building from 45 to 75% of FTP, in 5-minute steps. Add two 20-second pick-ups at the end so the first surge doesn't come as a shock.
Main set
39 min
3 × (10 × 40″ at 115–125% FTP, 20″ recovery), 5′ between sets
Three 10-minute blocks, with 5 easy minutes at 45–55% between them. Each block runs 10 times through 40 seconds at 115–125% of FTP, or 288 to 313 W for an FTP of 250 W, and 20 seconds at 50–60%. Aim for even power across all ten reps rather than a flashy start. On a turbo, resistance or slope mode follows quick changes better than ERG.
Cool-down
10 min
10′ at 40–55% FTP
10 very easy minutes at 40–55% of FTP. Let your breathing settle fully: the 20-second recoveries never allowed it during the blocks.

How it should feel

Very hard by the end of each block. The 40 seconds start to drag from the seventh rep, and the 20-second recoveries go so fast you'll wonder if your head unit is cheating. Guide: 9 out of 10.

Common mistakes

Riding it at 30/15 power

The efforts are a third longer: the power needs to come down a bit. Using your 30/15 watts on 40-second efforts will see you blow up in the middle of the second block.

Properly resting in the 20 seconds

Freewheeling lets your heart rate drop and makes the next surge harder. Spin easily at 50–60%: keeping your breathing high is what makes the session.

Going too hard in the first block

The first reps feel easy. Go over the range from the start and your third block will be well below the first, and the session loses its evenness.

Picking 40/20s for the evidence

No study has tested them as such. If you want a well-documented format, go for Rønnestad's 30/15; keep 40/20s for variety.

When to skip it

Before you start

A recently measured FTP.
A few short-interval or VO₂max sessions already done.

Skip it if

You're tired, or a race or long ride is planned for the next day.
You're new to VO₂max work: start with 15/15s or 30/30s.
You have doubts about your health: get medical advice before near-maximal efforts.

Origin and evidence

Level of evidence

Established practice, no dedicated studyLevel 1 of 5

A very common format among coaches and on training platforms, often mentioned alongside the 30/15. Its origin hasn't been traced to a primary source, and no dedicated scientific study has been found: so this page cites no source. Popular sources mention 110 to 130% of FTP for short intervals. The 115–125% range, slightly below the 30/15 because the efforts are longer, the number of blocks, the 5-minute recoveries, the warm-up and the cool-down are Wattson choices. Bottom line: weak evidence on origin and intensity, well-established practice.

Frequently asked questions

What power should I ride 40/20 intervals at?

115–125% of FTP for the 40 seconds, and 50–60% for the 20-second recovery. For an FTP of 200 W: 230 to 250 W. For 250 W: 288 to 313 W. For 300 W: 345 to 375 W. There's no reference intensity for this format: it's a Wattson choice, a little below the 30/15.

40/20 or 30/15: which should I choose?

Rønnestad's 30/15 has been studied in cyclists, with good results for VO₂max and performance. The 40/20 borrows its principle with longer efforts, but without a dedicated study. For a first session, go for the 30/15; the 40/20 is mostly for variety.

How many blocks of 40/20 should I do?

Three 10-minute blocks, or 20 minutes of work, for a rider who already knows this kind of session. To start with, use 8-minute blocks. Once all three blocks go by at even power, add a fourth block rather than raising the intensity.

Can I ride 40/20s outdoors?

Yes, on a flat road or a clear drag, with a power meter and the changes programmed on your head unit. Stay in the same gear and use cadence to surge. Avoid roads with junctions: thirty surges in a session need a quiet route.

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