CyclingVO2maxAdvanced 58 min

Variable-power VO₂max intervals on the bike (4 × 6 min)

Variable intensity VO₂max intervals: four 6-minute efforts, each made of three 30-second surges at 125–130% of FTP separated by 90 seconds at 102–106%, with 3 minutes' recovery between efforts. A 58-minute session for advanced riders.

Written by Pierre Halloo · Updated 25 October 2026

Session profile31 blocks

At a glance

Duration: 58 min
Main target: 102–130%FTP6 Z6 · Anaerobic
Time at target: 24 min
Estimated load: 66
Structure: 4 × (3 × (30″ at 125–130% FTP / 1′30 at 102–106% FTP)), 3′ between sets
Level: Advanced
Equipment: Power meter · Smart trainer

The session in detail

FTP

Time in zone

Z124 min
Z210 min
Z418 min
Z66 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
125–130%	6Anaerobic	6 min	250–260 W	313–325 W	375–390 W
102–106%	4Threshold	18 min	204–212 W	255–265 W	306–318 W
50–60%	1Recovery	9 min	100–120 W	125–150 W	150–180 W

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Wattson works out the targets from your FTP and sends the session to your Garmin, Wahoo, Coros or Suunto.

Try this session

What this session is for

During a steady interval, your breathing and oxygen uptake eventually level off, sometimes a little below their maximum. A 30-second surge in the middle of the effort pushes them back up, and the 102–106% spells that follow are hard enough to stop them dropping again. The expected result: more time near your VO₂max in each effort, for an average power and perceived effort close to a standard interval.

That's what a 2020 study in well-trained cyclists measured, within a single session. The principle is sound, but this exact format, 4 × 6 minutes with three surges, is Wattson's translation: the study's exact structure hasn't been checked.

Who it's for

Advanced riders who know VO₂max intervals well, like the 4 × 5 min, and want to change the shape without changing the goal. It also suits anyone who races in a bunch: surging on top of an effort that's already hard feels a lot like the attacks in a road race.

When to do it

One or two VO₂max sessions a week at most, and this counts as one. Keep an easy day before and after, and avoid the day before a race or long ride. To bring it in, start with three efforts, then four; the strongest riders go to five. Swap it from block to block with a classic 4 × 5 or a 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 a couple of short pick-ups at the end if you like, to get your legs ready for the surges.
Main set
33 min
4 × (3 × (30″ at 125–130% FTP / 1′30 at 102–106% FTP)), 3′ between sets
Four 6-minute efforts. Each one runs three times through 30 seconds at 125–130% of FTP, then 90 seconds at 102–106%, without a break. For an FTP of 250 W: 313 to 325 W on the surges, 255 to 265 W between them. Between efforts, 3 easy minutes at 50–60%. Surge seated or standing, whichever you prefer, but don't sprint. On a turbo, resistance or slope mode follows quick changes better than ERG, which takes a few seconds to react.
Cool-down
10 min
10′ at 40–55% FTP
10 very easy minutes at 40–55% of FTP. Your legs often sting more than after a steady interval: just let them spin.

How it should feel

The surges are hard, and the 102–106% spells give you no recovery: you're already above threshold when the next one arrives. The third surge of each effort feels like the longest of all, even though it's the same 30 seconds. Guide: 9 out of 10 by the end of each effort.

Common mistakes

Recovering between surges

Letting power fall to FTP or below after each surge turns the effort into a set of sprints. The 102–106% spells are the heart of the session: they keep your breathing up.

Sprinting the surges

125–130% isn't a sprint. Going flat out for 30 seconds makes the spells between impossible and blows the effort apart before the sixth minute.

Using ERG mode without anticipating it

In ERG, resistance takes a few seconds to catch up: the surge starts late and ends late. Switch to resistance or slope mode, or start each surge just before the change shows on screen.

Treating it like over-unders

Over-unders swing around your threshold for 12 minutes. Here everything happens above it: the low part is already 102–106%, and the surges go much higher. It's a different energy system at work.

When to skip it

Before you start

A recently measured FTP.
Several weeks of steady-power VO₂max intervals.

Skip it if

You're tired, or a race or long ride is planned for the next day.
Your only road has traffic or junctions: the surges need to land on time, not when the lights change.
You have doubts about your health: get medical advice before near-maximal efforts.

Origin and evidence

Level of evidence

Limited evidenceLevel 2 of 5

Bossi et al. (Int J Sports Physiol Perform 2020): in 14 well-trained cyclists, variable-power efforts produced more time above 90% of VO₂max (410 s against 286 s) than steady efforts at the same average power, with no difference in perceived effort. Another study from Rønnestad's group found a similar result. Both are single-session measurements. The exact structure used in the study hasn't been checked: this format follows its principle, power variations within the effort for an average of about 110% of FTP, but its durations and intensities, the warm-up and the cool-down are Wattson choices. Bottom line: good evidence for the principle, weak for this exact format.

Sources

Bossi A. H. et al., Int J Sports Physiol Perform 2020

Frequently asked questions

What power should I ride variable intensity VO2max intervals at?

Surges at 125–130% of FTP, spells between at 102–106%. For an FTP of 200 W: 250 to 260 W, then 204 to 212 W. For 250 W: 313 to 325 W, then 255 to 265 W. For 300 W: 375 to 390 W, then 306 to 318 W. Don't drop below your FTP between surges.

Variable or steady power: what's the difference?

The time you spend near VO₂max in each effort. At steady power, your breathing peaks and then levels off; regular surges push it back up. Measured in well-trained cyclists, that meant more time near the maximum for a similar perceived effort. Whether the advantage holds over several weeks hasn't been tested yet.

Fast start or variable intensity: which should I choose?

The fast start puts all the extra intensity at the beginning, then lets you hold a steady power: easier to pace. Variable intensity spreads three surges through the effort: closer to bunch racing, and harder on your head. Both chase the same thing; alternate them if you like variety.

Which turbo trainer mode should I use for this session?

Resistance or slope mode, using your gears, follows 30-second changes better. ERG works, but it takes a few seconds to adjust the resistance, which shifts every surge. If you stay in ERG, start pushing just before the change appears on screen.

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