The 4x4 VO2max workout: origins and how to run it

Sixteen minutes of hard running does not sound like much. Then you start the third interval, your legs feel like wet sand, and the three-minute jogs between reps are the only thing holding you together. They never feel long enough.

The 4x4 VO2max workout is four intervals of four minutes each at 90 to 95% of your maximum heart rate, with three minutes of easy jogging between them. Warm up before it, cool down after, and run it about once a week.

Where the 4x4 comes from

The protocol comes out of Norwegian exercise physiology. A research group at the Norwegian University of Science and Technology (NTNU) in Trondheim, led by Jan Helgerud and Jan Hoff, tested it against other ways of training. Their 2007 paper in Medicine & Science in Sports & Exercise is the one most people cite.

Forty moderately trained men were split into four groups of ten. One group ran long and slow at about 70% of max heart rate. One ran continuously at lactate threshold, about 85%. One did 15 seconds hard, 15 seconds easy, repeated. The fourth did the 4x4: four minutes at 90 to 95% of max heart rate, then three minutes of active recovery at about 70%. Everyone trained three days a week for eight weeks, and the programs were matched for total oxygen cost.

Absolute VO2max rose 7.2% in the 4x4 group (from 4.56 to 4.89 litres per minute) and 5.5% in the 15/15 group. The long slow group and the threshold group showed no change. Per kilogram of body weight, the 4x4 group average went from 55.5 to 60.4 mL/kg/min. Stroke volume, the amount of blood the heart pushes out per beat, rose about 10% in the two interval groups.

Two caveats. The subjects were moderately trained men, not Olympians, and ten people per group is small. The three sessions a week were a research protocol and not a training recommendation. The study shows the 4x4 can raise VO2max in a short window. It says nothing about how many sessions a week are best. Since then the session has become a common part of Norwegian-style endurance training.

What VO2max is and why this workout targets it

VO2max is the highest rate at which your body can take in and use oxygen. Two things limit it: how much blood your heart can deliver, and how well your muscles pull oxygen out of that blood. A widely cited 2000 review by David Bassett and Edward Howley concluded that oxygen delivery, and not the muscles' ability to extract oxygen, is the primary limit on VO2max, which is why the stroke volume finding matters.

Raising delivery means spending real time with your heart working near its maximum output. Oxygen uptake needs time to climb at the start of hard running, so a four-minute rep spends more of its length near the ceiling than a short rep like a 400 does. The three-minute jog lets your heart rate fall without dropping to a standstill, so each new rep starts from a high baseline and gets back to the ceiling fast. That is why the recovery is a jog and not a walk. The study protocol used active recovery at about 70% of max heart rate.

Setting your heart rate targets

Start with your maximum heart rate. A field test is better, but most people use a formula. The Tanaka formula (208 minus 0.7 times your age) holds up better across ages than the old 220 minus age rule.

A 30-year-old gets 208 - 21 = 187 bpm. Here is how the numbers fall out:

| Target | Percent of max | Heart rate | |--------|---------------|------------| | Work intervals (research protocol) | 90 to 95% | 168 to 178 bpm | | Recovery jog | about 70% | about 131 bpm |

In StartLane's five-zone model, Zone 4 is VO2max and spans 90 to 96% of max heart rate, so for this runner that is roughly 168 to 180 bpm. Zone 3 is threshold and sits just below, at 82 to 90%.

Heart rate lags effort. At the start of a four-minute rep it is still climbing from the jog and will not reach the target until somewhere in the second minute. Run the first minute by feel, controlled and strong, and let the number catch up. If your heart rate is at the top of the range with a minute to go, back off a few seconds per mile instead of grinding.

How to run the session

1. Warm up for 10 to 15 minutes. Start very easy, then add a few minutes at moderate effort and two or three short pickups. Walking straight into rep one is how people pull a calf.
2. Run four reps of four minutes at the target heart rate. Pick a flat stretch, a track, or a gentle uphill. Hills lower the pace for the same effort and are easier on the legs.
3. Jog three minutes between reps, truly easy, near 70% of max.
4. Cool down for 10 minutes at easy effort.

Total time is about 40 minutes. Do not stretch the 16 minutes of work to 20 because you feel good on rep two.

The rep to protect is the fourth. If rep one feels comfortable and rep four is a crawl, you started too fast. All four reps should finish at about the same pace and heart rate, with the last one hard but not out of control. If you could have done one more rep at a clearly slower pace, you ran it about right.

How often to do it

Once a week is enough for most runners. Stephen Seiler's research on elite endurance athletes found that most of them keep about 80% of their sessions easy and about 20% hard. For a runner training five days a week, that means one or two hard sessions. If one is a 4x4, the other can be threshold work, and everything else stays easy.

Seiler's 2010 review also found no convincing evidence that putting more emphasis on high-intensity intervals gives long-term gains in already well-trained athletes. A second 4x4 in the same week is more likely to add fatigue than fitness, so leave at least a couple of easy days between hard sessions.

Do not start here. Run consistently for several weeks first, with easy running and some threshold work, because a 4x4 on top of no base is a good way to get hurt. Give yourself an easy day on each side of it, and keep it out of race week. The 4x4 belongs in the build phase, a few weeks out. In the final stretch you protect your legs.

Mistakes that ruin the session

Running by pace instead of heart rate is the first. On a hot day, the pace that puts you at 172 bpm is slower than on a cool morning, and chasing a pace from last month in July means you will blow up on rep three.

Skipping the jog is the second. If you stand for two minutes, your heart rate falls far enough that rep two starts from a lower baseline and the effort is no longer continuous.

Too much of everything else also undoes it. The 4x4 works when the other days are easy. If you run medium-hard on your easy days, you arrive at the session tired and cannot reach the target heart rate, or you reach it at an unhealthy cost. Our guide to why you are running too hard on easy days covers the fix.

A threshold run is not a VO2max run. Threshold intervals are longer, a little slower, and feel controlled. For details on that side, read what lactate threshold is and why it matters.

Finally, pay attention to how you feel. If your resting heart rate is up, your sleep was bad, or your legs are sore from earlier in the week, move the session a day. One hard session done well beats two done badly.

Anyone with a heart condition, or who has not exercised hard in a long time, should talk to a doctor before doing max-effort intervals.

How StartLane handles it

StartLane uses the same zone model described above. Zone 4 is VO2max, Zone 3 is threshold, and your zones come from your max heart rate, either the Tanaka estimate from your age or a number you enter yourself.

In the 8-week Norwegian Method block, the 4x4 first appears in week 5 and repeats in weeks 6 and 7, one session per week, alongside the threshold work. Week 8 is a lighter test week so you can see how your pace at a given heart rate has changed. Each 4x4 session in your plan shows the warm-up, your Zone 4 heart rate range, an estimated pace for those reps, and the three-minute recovery at about the top of your Zone 1 range (the study used about 70% of max). The 5K and 10K race plans built on the Norwegian style also include one 4x4 a week in the build and peak phases and drop it before race week.

The pace is an estimate based on your fitness inputs, so treat the heart rate range as the target and the pace as a rough guide. You can log each session by hand or sync from Strava with the sync button. The daily check-in (readiness, sleep, soreness, and HRV) gives you something to look at before you decide whether today is the day to run it.

What Is the Norwegian Method? lays out the weekly structure around it.