The interval length debate is over. Sort of.

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Your five-minute intervals might be a waste of time.

If you have been doing four-by-five or five-by-five-minute intervals as your bread-and-butter VO2max work, you are not alone. It is probably the most common interval prescription in cycling. And for years, the logic was simple: longer efforts mean more time at high oxygen consumption, which means a bigger aerobic stimulus.

Except that is not quite what the research says anymore.

A network meta-analysis published in 2025 in BMC Sports Science, Medicine and Rehabilitation pooled data from 51 studies covering 1,261 athletes. They compared three types of interval training: traditional high-intensity intervals (HIIT), sprint interval training (SIT), and repeated sprint training (RST). All three significantly improved VO2max compared to conventional training.

But here is the finding that changes how you should think about your sessions: the optimal work interval duration for HIIT was 140 seconds, with a work-to-recovery ratio of 0.85. That means roughly two minutes and twenty seconds of work, followed by about two minutes and forty-five seconds of recovery.

Not five minutes. Not three minutes. Two minutes and twenty seconds.

And that is not the only study pointing in this direction.

In 2024, Solli, Rønnestad and colleagues published a study in the European Journal of Sport Science looking at well-trained cyclists performing a six-day block of 30/15 intervals (thirty seconds hard, fifteen seconds easy, repeated in sets of 8 minutes 45 seconds). Compared to a control group doing regular training with the same number of hard sessions, the short-interval block group improved their power output at VO2max by 3.7% (versus 0.7% in the control group, p = 0.009, effect size = 1.00). They also improved ten-second sprint power by 2.8%.

And in earlier work from the same Norwegian lab, Appelhans, Rønnestad and Skovereng tested twelve well-trained cyclists and triathletes (VO2max of 68 ml/kg/min) and found that the time spent near VO2max was similar between short intervals (3 x 13 x 30/15 seconds) and long intervals (6 x 5 minutes with 2:30 recovery). Same stimulus. Very different session structure.

Here are three things worth sitting with:

1. The "sweet spot" for interval duration is shorter than most cyclists think. The meta-analysis found an inverted U-shaped relationship between interval length and VO2max improvement. Too short and you do not accumulate enough stimulus. Too long and fatigue degrades the quality of the effort. 140 seconds sits right at the peak. For most cyclists, that means your classic five-minute intervals are overshooting the optimal duration by more than double.

2. Short intervals can deliver the same or better stimulus with less perceived suffering. This is the practical win. A session of 30/15s or two-to-three-minute efforts with matched recovery is physiologically equivalent to long intervals, but it is psychologically easier to execute well. You can hold better form, maintain higher relative intensity, and accumulate quality work without the mental dread that comes with staring down a five-minute block.

3. The adaptation is real, not just acute. The Solli study was not measuring what happened in a single session. It measured performance changes after a training block. The 3.7% improvement in power at VO2max is a meaningful, measurable shift in fitness. And it came from 30/15s, not the long efforts most people assume are required.

What to do with this

If you race or do hard group rides: Consider replacing one of your long-interval sessions per week with a short-interval alternative. A session like 3 to 4 sets of 8 to 9 minutes of 30/15s (thirty seconds at roughly 120% of your 40-minute power, fifteen seconds easy) gives you a potent VO2max stimulus with better execution quality. You still need some longer efforts for race specificity, but the idea that five-minute intervals are the only path to a bigger engine is outdated.

If you train big hours: Short intervals slot into a big training week more easily than long ones. They create less residual fatigue, which means the rest of your training week holds up better. If you are doing two quality sessions per week inside a high-volume block, making one of them a short-interval session is a smart way to keep the stimulus high without blowing up your recovery.

If you are time-capped: This is arguably where short intervals shine most. A 60-minute session with a good warm-up and three sets of 30/15s gives you a genuine VO2max stimulus in under an hour. You do not need a two-hour ride with long intervals to get meaningful aerobic adaptation. For the rider with six to eight hours a week, this is a game changer.

Bottom line: The best interval is not the longest one. It is the one you can execute at the highest quality, for the right duration, with the right recovery. And the evidence says that duration is closer to two and a half minutes than five.

References: BMC Sports Science, Medicine and Rehabilitation (2025). Comparison of different interval training methods on athletes' oxygen uptake: a systematic review with pairwise and network meta-analysis. 51 studies, 1,261 athletes. Solli, G.S., Odden, I., Sælen, V., Hansen, J., Mølmen, K.S. & Rønnestad, B.R. (2024). A microcycle of high-intensity short-interval sessions induces improvements in indicators of endurance performance compared to regular training. European Journal of Sport Science. Appelhans, D., Rønnestad, B.R. & Skovereng, K. (2021). Time spent near VO2max during different cycling self-paced interval training protocols. Norwegian University of Science and Technology.

On my mindProve It First

I had a great call with an athlete this week. One of those conversations where you start talking about training and end up somewhere much deeper.

We were talking about confidence. The kind that lets you commit to a move in a race, hold a wheel when it hurts, or back yourself on a day when the legs are not shouting yes.

And the thing I keep coming back to is this: confidence is not something you find. It is something you prove.

You prove it to yourself. Through small promises kept. Through setting out to do something and doing it. Not perfectly. Not spectacularly. But consistently. Every time you say you will do a session and you do it, that is a deposit. Every time you set an intention for a ride and you follow through, that is a brick in the wall.

And when you break a promise to yourself, even a small one, that is a withdrawal. It chips away at something. Not fitness. Something else.

I have thought about this a lot, partly because I studied psychology and partly because I see it play out with athletes all the time. There is a framework I keep coming back to that I think is worth sharing.

When you think about the past, that is your ego. What you have done. What you have been.

When you think about the future, that is your pride. What you believe you can become.

When you think about the present, that is humility. What you are willing to do right now, today, with what you have.

Confidence lives somewhere in the overlap of all three. But I think the one most people neglect is the present. The willingness to be here, fully, in this session, on this ride, and execute with intention.

Which brings me to something else. I think comfort is the enemy of confidence. If you are doing the same sessions, racing the same people, riding the same roads, you might feel safe. But safe does not build belief. Changing something carries a risk, sure. It might go worse. But it also opens the door to seeing something new inside yourself. And that is where real confidence comes from.

Sometimes, as a coach, I think the best thing I can do is not push someone to the edge. It is to pull them back slightly, give them something they can absolutely nail at a high level, and let them walk away hungry. Not destroyed. Not hanging on. But confident. Proven. Ready for the next step.

That is what I have been thinking about this week.

Damian