Classic VO2max training is four to five reps of five minutes at the edge of throwing up. It works, but it has a flaw: by the time you find your rhythm, the hardest minutes are already behind you, and oxygen uptake has barely reached its ceiling. Norwegian Bent Rønnestad proposed something smarter: 30/15 microintervals. You suffer for less time in each single rep, and you spend more time in the zone where the adaptations actually happen.
What the protocol looks like
The scheme from Rønnestad and Hansen’s research is simple: three sets of thirteen reps of 30/15, that is 30 seconds hard, 15 seconds easier, repeated thirteen times in a row. Three minutes of rest between sets. One set is just over nine minutes of work, and the whole session fits inside an hour including warm-up and cool-down.
The key point: those 15-second “breaks” are not rest. Heart rate is not meant to drop. That’s why after a few reps, oxygen uptake climbs close to VO2max and stays there, and it’s time spent above 90% of VO2max that drives the adaptation.
What power to hold
The specifics, because without them this is just theory:
- 30 seconds “on”: about 110% of threshold (FTP), roughly the power you could hold for a single maximal five-minute effort.
- 15 seconds “off”: about 50% of threshold, keep pedalling, don’t stop.
- Feel-based check: aim for RPE 9/10 and above 88% of max heart rate as a proxy for 90% VO2max (heart rate lags, so only read it from the second half of a set onward).
Start sensibly. First attempts should be two to three sets of nine reps, adding reps and power week by week. Before the first set, add one or two one-minute efforts at 110 to 120% of threshold to “wake up” the aerobic system, so the first set isn’t wasted just finding your rhythm.
Does 30/15 actually beat long intervals? No spin
Time for honesty here, because the internet loves an “8% gain” headline. In a 2015 study (trained cyclists, ten-week programme), the group doing 30/15 improved VO2max by 8.7%, while the group doing classic 4×5-minute intervals improved by only 2.6%. Impressive, but that is one study, on one population.
A later Rønnestad paper from 2020, on 18 elite national-level cyclists (VO2max around 68 to 77 ml/kg/min), found no difference in VO2max gains between short and long intervals, though the short format produced a bigger gain in 20-minute test power. The more highly trained the athlete, the harder it gets to see a dramatic jump in VO2max itself, whatever the format.
The practical conclusion: 30/15 is a very good tool, not magic. Its real edge for an amateur isn’t the mythical percentages, it’s that it’s easier to finish at good quality. Short reps unravel technique and focus less than the fifth minute of the fifth “five” does. A session you actually complete properly always beats the one that’s perfect on paper.
Fitting it into the week
One, at most two, of these sessions a week, on fresh legs, with at least one easy day around it. On the bike, trainer or a flat stretch, it comes out cleaner than on the run, because power is easier to hold and there are no junctions to deal with. On the run you can carry the same scheme over to time or pace, but let go of chasing watts and watch breathing and RPE instead.