RunningSpeed and sprintsAdvanced 47 min

Anaerobic capacity: 6 × 45 s at 120% of vVO₂max

Anaerobic capacity running intervals: six 45-second efforts at 118–125% of vVO₂max, with 3 min 30 of walking between. A 47-minute session for running very fast for 30 seconds to 2 minutes, and holding on through the burn at the end of an 800 m or 1500 m.

Written by Pierre Halloo · Updated 25 October 2026

Session profile14 blocks

At a glance

Duration: 47 min
Main target: 118–125%vVO₂max7 Z7 · Neuromuscular
Time at target: 5 min
Estimated load: 37
Structure: 6 × 45″ at 118–125% vVO₂max, 3′30 recovery
Level: Advanced
Equipment: GPS watch · Track (optional)

The session in detail

vVO₂max

Time in zone

Z138 min
Z25 min
Z75 min

What the targets mean

The session's targets, as paces for three reference speeds
Target	Zone	Time	vVO₂max 14 km/h	vVO₂max 16 km/h	vVO₂max 18 km/h
118–125%	7Neuromuscular	5 min	3:38/km–3:26/km 207–219 m per rep	3:11/km–3:00/km 236–250 m per rep	2:49/km–2:40/km 266–281 m per rep
25–35%	1Recovery	18 min	17:09/km–12:15/km 204–286 m per rep	15:00/km–10:43/km 233–327 m per rep	13:20/km–9:31/km 263–368 m per rep

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What this session is for

Above your vVO₂max, your aerobic system can't keep up: a growing share of the energy comes from the anaerobic system, which delivers fast but runs out fast, and brings on the burn in your thighs. Working in this zone improves your ability to run very fast for one to two minutes, and to put up with it.

The session is built from published principles, not from a study protocol. At this intensity, runners last around two minutes on average before exhaustion. A 45-second effort is therefore about a third of that limit: enough to tax the system, short enough to repeat six times thanks to the long walk.

Who it's for

Experienced middle-distance and 5K runners preparing for a race where the finish comes down to speed. You need a recently measured vVO₂max: every distance depends on it. Not for beginners, or when coming back from a break.

When to do it

One session a week at most, with two days before another hard session, and never the day before a race. It belongs in the weeks before your middle-distance races, once your VO₂max base is built.

How to do it

Warm-up
15 min
10′ at 60–65% vVO₂max + 5′ at 66–72% vVO₂max
10 minutes of easy running at 60–65% of vVO₂max, then 5 minutes at 66–72%, with a few gradual strides. On a track, mark your distance: at 16 km/h, 236 to 250 metres, a little over half a lap.
Main set
22 min
6 × 45″ at 118–125% vVO₂max, 3′30 recovery
Six 45-second efforts at 118–125% of vVO₂max, each followed by 3 min 30 of walking. At 16 km/h, that's 236 to 250 metres, between 3:11 and 3:00/km. Start fast but don't blow up: the speed should stay the same from the first metre to the last, and from one effort to the next. If it drops clearly, the session ends there. The walk is long, and it's what lets you keep the quality.
Cool-down
10 min
10′ at 55–65% vVO₂max
10 minutes of very easy running at 55–65% of vVO₂max. Compare your distances: if all six are close, you can add an effort next time; if not, stick with six and work on your start.

How it should feel

The burn arrives in your thighs from about thirty seconds, and the last seconds of each effort are heavy: stride shortening, arms tightening. The 3 min 30 walk feels long at first, then only just long enough. Guide: 9 out of 10.

Common mistakes

Blowing up in the first 15 seconds

Too fast a start has you holding a wild speed for 20 seconds, then collapsing. The session asks for even speed over 45 seconds: that's what trains you to hold the end of a race.

Jogging instead of walking

The walked recovery is long for a reason: to get fresh enough to run the next effort at the same speed. Jog it and the session becomes something else, with your speed dropping from the third effort.

Doing it too early in the season

It's a sharpening session. Without an endurance and VO₂max base, it tires you out for little gain. Put it in the weeks before your races.

Stacking it with another hard session

The fatigue from an anaerobic session often shows two days later. Leave two days before your next hard session, and never put it the day before a race.

When to skip it

Before you start

A recently measured vVO₂max: every distance depends on it.
A VO₂max base already built, with short and long intervals.

Skip it if

You're new to running, or coming back after a break.
You have pain or a recent injury.
A race or another hard session is planned within two days.

Origin and evidence

Level of evidence

Limited evidenceLevel 2 of 5

A session built from published principles. Billat (Sports Med 2001;31(2):75-90) describes anaerobic interval training above vVO₂max. Blondel, Berthoin, Billat and Lensel (Int J Sports Med 2001;22(1):27-33), 10 subjects, measured time to exhaustion at 90, 100, 120 and 140% of vVO₂max: about 122 ± 27 seconds at 120%, against 65 ± 17 seconds at 140%. Daniels prescribes fast repetitions with long recoveries. No published protocol in the 6 × 45-second format was found: the durations, the 118–125% range, the recovery of about 4.7 times the effort, the variations at 125% over 30 seconds and 112% over 60 seconds, the warm-up and the cool-down are Wattson choices. Bottom line: weak evidence on the format, moderate on the principles, the relationship between speed and time to exhaustion.

Sources

Billat V. L., Sports Med 2001;31(2):75-90
Blondel N., Berthoin S., Billat V., Lensel G., Int J Sports Med 2001;22(1):27-33
Daniels J., Daniels' Running Formula, Human Kinetics

Frequently asked questions

How fast should the 45-second efforts be?

At 118–125% of your vVO₂max. In 45 seconds, that's 207 to 219 metres at 14 km/h, 236 to 250 metres at 16 km/h, 266 to 281 metres at 18 km/h. On a track, use these distances as markers: aim for the same on every effort.

What is anaerobic capacity?

It's the amount of energy your muscles can produce without oxygen, over very hard efforts lasting a few dozen seconds to around two minutes. It matters over 800 m and 1500 m, and in the closing stages of longer races. The burn you feel is part of it.

Why such a long recovery?

To keep the same speed across all six efforts. A 45-second effort at this intensity drains a lot of your fast energy stores; they take several minutes to partly rebuild. With a short recovery, you'd be doing a slower fatigue-tolerance session instead.

Is this session useful for a 10K?

Not much. Over 10K, what matters most is your threshold and your VO₂max. This session mainly serves races from 800 m to 5K, and sprint finishes. For a 10K, 10K-pace intervals are more directly useful.

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