Run intervals at 90 to 95% of your max heart rate. That's what raises VO₂ max: in the trial that held total work constant across four intensities, only the two interval groups improved, and easy and threshold running changed nothing.
What is VO₂ max and why does it matter?
VO₂ max is the most oxygen your body can use in a minute. Every pace you run costs a share of it, so a higher ceiling makes the same pace cheaper: easier to hold, and easier to repeat.
The VO₂ max number on a watch is an estimate, not a measurement.
When your VO₂ max rises, most of the change is in your heart. In exercise physiologist Jan Helgerud's training trial, interval training raised stroke volume, the blood the heart moves per beat. Easy and threshold running didn't change it. Your max heart rate doesn't move with training, the same paper notes, so the gain has to come from what each beat delivers.
Do easy runs raise VO₂ max?
In the trial that tested it directly, no. Helgerud's team had four groups train 3 days a week for 8 weeks, every group doing the same total work, measured as oxygen cost. Nothing differed between them but how hard they ran.
Helgerud 2007: same work, different intensity
40 moderately trained young men, treadmill running, four groups matched for total oxygen cost.
| Group | VO₂ max change | Stroke volume |
|---|---|---|
| 4x4 intervals (90–95% HRmax) | +7.2% | +10% |
| 15/15 intervals (47 x 15 s, 90–95% HRmax) | +5.5% | +10% |
| Lactate threshold (85% HRmax) | No significant change | No significant change |
| Long slow distance (70% HRmax) | No significant change | No significant change |
The figures are the trial's results, not a promise of your gain.
With total work held equal, the easy miles didn't move VO₂ max, and neither did threshold pace. Intensity alone separated the groups.
How hard should VO₂ max intervals be?
90 to 95% of your max heart rate. That's the band both groups that improved held in Helgerud's trial, and it's the intensity the paper itself prescribes.
On the five-zone model, Zone 4 tops out at 90% of max, so the band runs from the Zone 4 ceiling into the lower half of Zone 5. Start at the top of Zone 4. Through an interval your heart rate will climb into Zone 5, and that's what you want.
Just below the band, at 85% of max in the same trial, nothing significant changed, and that trial didn't test the space between 85 and 90%.
RunBeat's Timed Intervals runs the clock for you, calling every work and rest phase by voice, with zone announcements on top if you want them:
Timed Intervals in RunBeat
RunBeat calls every work and rest phase, and your Apple Music playlists switch with it.
Norwegian 4x4, Billat 30/30, or Tabata: what's the difference?
Interval length and what sets the intensity. The 4x4 holds 4-minute reps in a heart rate band, the 30/30 alternates half-minutes at a fixed pace, and Tabata takes you to exhaustion, on a bike.
Norwegian 4x4
Four 4-minute intervals at 90 to 95% of max heart rate, with 3 minutes of easy jogging at about 70% between them. In the spec Helgerud's trial ran, the recovery is a jog, not standing rest.
In a seven-week trial with 35 trained recreational cyclists, 32 minutes of work per session at about 90% of peak heart rate outgained the 4x4's 16 minutes at about 95%: pooled gains of 11.4% against 5.5% across three fitness measures.
Here's how to hit that band four times over, and what your heart rate does inside each rep:
How do you run the Norwegian 4x4?
Four 4-minute intervals at 90 to 95% of max heart rate, 3 minutes of jogging between, four times.
Billat 30/30
French exercise scientist Véronique Billat built the 30/30 around vVO₂ max, the slowest pace that draws your full VO₂ max. In elite middle-distance runners it sits close to 3,000 m race pace. Held continuously, that pace is good for about 6 minutes on average, with around 25% variation from runner to runner.
The session alternates 30 seconds at vVO₂ max with 30 seconds of jogging at half that pace. The recovery is deliberately a jog rather than a rest, so your oxygen uptake stays high between reps.
In 12 highly trained middle-distance runners on a treadmill, 24 x 30 seconds at vVO₂ max with a 55% jog held oxygen uptake above 90% of VO₂ max for about three and a half minutes, against about five and a half for 4 x 3 minutes at 95% of vVO₂ max.
In Billat's study of eight endurance-trained male runners, the intermittent session held them at VO₂ max for 7 minutes 51 seconds. The continuous comparison run managed 2 minutes 42 seconds, and that one was hard too, at about 91% of vVO₂ max.
Finding your own pace for it, and what your heart rate does across the reps:
How do you run the Billat 30/30?
30 seconds at the slowest pace that draws your full VO₂ max, 30 seconds of jogging at half that pace, 16 to 20 times.
Tabata
The original protocol is 7 to 8 bouts of 20 seconds with 10-second rests, and the definition is the intensity: hard enough to exhaust you by the 7th or 8th bout. The original work put that at a nominal 170% of VO₂ max, and Tabata's own review says the training doesn't require that exact figure.
It was developed for the bike, out of the training of Japan's national speed skating team under head coach Kouichi Irisawa. For running versions, the review calls the published evidence insufficient.
The 20/10 timing alone isn't the workout. The review's own example is walking on that pattern at under 30% of VO₂ max, and there's no improvement to expect from it. At the intensity the definition requires, the review calls the training very demanding and limits it to highly motivated athletes.
How do VO₂ max intervals fit with Zone 2 training?
As base and ceiling, not rivals for the same slot. Zone 2 training carries most of the week: easy volume that keeps you recovering between hard days and makes an interval block sustainable. The intervals raise the ceiling, and that's the one thing the work-matched trial showed easy miles alone don't do.
Do only intervals and you skip the base that makes hard days repeatable. Run only easy and you leave the top end untouched. If the base isn't there yet, build the aerobic base first and add intervals on top.
Sources
- Helgerud J, et al. Aerobic high-intensity intervals improve VO₂max more than moderate training. Medicine & Science in Sports & Exercise. 2007;39(4):665-671. doi:10.1249/mss.0b013e3180304570. 40 moderately trained young men, treadmill running, 3 sessions a week for 8 weeks, the four programs matched for total oxygen cost. Source for the 90-95% band (the paper's own prescription wording), the +7.2% and +5.5% outcomes, the no-change results at 85% and 70% of max heart rate, the 4x4 and 15/15 specs, and the stroke-volume rise, which was measured in a subset of six per group. The max-heart-rate sentence paraphrases its discussion. Full text read September 2026.
- Billat VL, et al. Intermittent runs at the velocity associated with maximal oxygen uptake. European Journal of Applied Physiology. 2000;81(3):188-196. doi:10.1007/s004210050029. Eight endurance-trained male runners. Source for the 30/30 spec, with the recovery a jog at 50% of vVO₂ max by design, and for the time-at-VO₂-max pair, printed as the paper's own stated figures; the continuous comparison run sat at about 91% of vVO₂ max, a hard run, not an easy one. Full text read September 2026.
- Billat LV, Koralsztein JP. Significance of the velocity at VO₂max and time to exhaustion at this velocity. Sports Medicine. 1996;22(2):90-108. Review. Source for the about-6-minutes figure, an average across studies of mixed populations and exercise modes with individual variation around 25%, never a personal prediction; and for the 3,000 m gloss, which the running literature (Daniels, Padilla, Lacour) states for elite middle-distance runners. Full text read September 2026.
- Fleckenstein D, Braunstein H, Walter N. Faster intervals, faster recoveries - intensified short VO₂max running intervals are inferior to traditional long intervals in terms of time spent above 90% VO₂max. Frontiers in Sports and Active Living. 2025;6:1507957. doi:10.3389/fspor.2024.1507957. 12 highly trained middle-distance runners, 7 men and 5 women, on a treadmill, in a randomized crossover: 24 x 30 s at 100% of vVO₂ max with 30 s at 55% between, against 4 x 3 min at 95% with 3 min at 50%. Source for the one comparison sentence in the 30/30 entry, the time each session spent above 90% of VO₂ max. Its heart-rate figures are not stated on this page. Full text read September 2026.
- Tabata I. Tabata training: one of the most energetically effective high-intensity intermittent training methods. Journal of Physiological Sciences. 2019;69(4):559-572. doi:10.1007/s12576-019-00676-7. Source for the exhaustion-based definition, the nominal 170% figure and its non-requirement, the cycling origin under coach Kouichi Irisawa, the insufficient-evidence scoping for running versions, and the low-intensity walking example. No outcome figure from it appears on this page. Full text read September 2026.
- Seiler S, et al. Adaptations to aerobic interval training: interactive effects of exercise intensity and total work duration. Scandinavian Journal of Medicine & Science in Sports. 2013;23(1):74-83. 35 trained recreational cyclists over seven weeks. Source for the closing comparison sentence; the 11.4% and 5.5% are pooled gains across VO₂ peak, power at VO₂ peak, and power at a fixed lactate level, not VO₂ max alone. Abstract read September 2026; the full text is closed at every legitimate route checked, and the abstract carries every figure stated here.