“VO₂max intervals are a killer workout, but after 40 you won’t survive without them” — that is how the Russian running channel s10.run teased a discussion of maximal oxygen uptake last week. The argument over which repeats are the “right” ones — 400 metres, a kilometre or 30/30 — never dies down in running chats. A fresh meta-analysis gives one of the most careful answers to it so far, though not the final one.

Why count time at the ceiling

For VO₂max to improve, the heart and muscles need to work close to their limit on a regular basis. So physiologists have long measured not just “how many intervals there were” but how many minutes per session oxygen uptake stayed near its maximum — usually above 90% VO₂max. The logic is simple: more minutes at the ceiling means a stronger stimulus.

The problem is that individual studies compared only two or three formats at a time, which made it hard to see the big picture.

What the researchers did

Schoenmakers, Bossi and co-authors (BMC Sports Science, Medicine and Rehabilitation, 2026) combed through PubMed and Scopus up to September 2025 and found 86 studies with 239 interval protocols — running, cycling, rowing and swimming. The participants were healthy and mostly male.

The protocols were split into three groups by the length of the work bout:

short — 30 seconds or less (for example, 30/30 or 15/15);
medium — from 30 seconds to 2 minutes (200–400 metres for most recreational runners);
long — 2 minutes or more (for most recreational runners, 600 metres and longer).

They also compared active and passive recovery, and an even pace within the work bout versus a variable one.

What they found

Long repeats came out on top. On average they produced about 555 seconds (≈9 minutes) above 90% VO₂max per session, versus 336 seconds for short and 322 seconds for medium repeats. The difference held even after adjusting for total work duration.
A variable pace within the repeat added time at the ceiling compared with an even pace (standardised mean difference 0.80 — a sizeable effect). An example of such a repeat: a fast start, then holding just below that.
The type of recovery didn’t matter. Jogging or standing between repeats had no effect on time at the ceiling.
Of the 239 protocols, 133 reached at least 5 minutes at VO₂max and 48 reached at least 10 minutes.

What not to believe too firmly here

Repeat length and total duration explained only about 7% of the differences between protocols. The rest comes down to individual traits, fitness and measurement methods. Two people doing exactly the same session can spend very different amounts of time at the ceiling.

The metric itself is shaky. Studies defined “at the ceiling” differently and smoothed the data differently, and the authors rate the reliability of the measure as low to moderate. The spread between studies was large.

An acute response is not an adaptation. The meta-analysis measures what happens in a single session, not how VO₂max grows over months. The authors themselves note that VO₂max can improve without a fixed “dose” of minutes at the ceiling. A telling example is the Norwegian study by Rønnestad and colleagues (Scandinavian Journal of Medicine & Science in Sports, 2015): over 10 weeks in cyclists, short 30/15 repeats produced bigger gains in power and VO₂max than 4 × 5 minutes at a comparable load.

The sample is mostly men, and there is hardly anyone over 50.

How to apply this

The default option is repeats of 2 to 5 minutes. For a recreational runner that means 600–1200 metres at a pace you could hold for 6–8 minutes straight. 4–6 such repeats give you a real chance of banking several minutes at the ceiling.
Don’t shy away from short repeats. 30/30 and 30/15 give less time at VO₂max per session, but they are easier to handle technically and mentally, and in Rønnestad’s multi-week study (described above) they actually came out ahead. Alternate formats from one training block to the next.
Try a “fast start”. Run the first 20–30 seconds of each repeat a little faster and the rest at target pace. That way oxygen uptake reaches its maximum sooner.
Recover however you like. Want to jog — jog; want to stand — stand. What matters more is that the next repeat is a quality one.
Don’t overdo these sessions. One or two a week on top of plenty of easy running is enough. For more on distributing intensity, see our piece on polarized versus pyramidal training.
Base your pace on your actual fitness. The VO₂max calculator will give you a guide from a race result, and the zones generator will set your zone boundaries. We explained why VO₂max matters for health as you age in a separate article.

The bottom line

A 2026 meta-analysis: 86 studies, 239 interval protocols.
Repeats of 2 minutes or more give about 9 minutes above 90% VO₂max per session; short and medium ones give 5–6 minutes.
A variable pace within the repeat adds time at the ceiling; the type of recovery makes no difference.
The metric is shaky: repeat length and total duration explain only about 7% of the differences between protocols, and in a multi-week study short repeats also built VO₂max. The best protocol is the one you do regularly and well.

Sources: Schoenmakers P., Murray K., White J., Matta G., Bossi A.H. “Time spent at or near V̇O₂max during high-intensity interval training — a systematic review and meta-analysis”. BMC Sports Science, Medicine and Rehabilitation, 2026;18. DOI: 10.1186/s13102-026-01766-x · Rønnestad B.R., Hansen J., Vegge G., Tønnessen E., Slettaløkken G. “Short intervals induce superior training adaptations compared with long intervals in cyclists — an effort-matched approach”. Scandinavian Journal of Medicine & Science in Sports, 2015;25(2):143-151. DOI: 10.1111/sms.12165