Increasing your VO2max: what 4x4 intervals really deliver

Four times four minutes hard, with three easy minutes between them. That protocol raised VO2max by 7.2 percent in eight weeks, while easy distance running at the same total workload produced no measurable gain (PMID 17414804).

That is a large difference for the same time on the road.

I still see people run the same loop at the same pace four times a week and wonder why their watch has said 44 for a year.

What raises your VO2max fastest?

Intervals at 90 to 95 percent of your maximum heart rate, in blocks long enough to load your heart properly. Helgerud and colleagues compared four training formats at the same total workload. The two interval formats won clearly; the two continuous formats produced nothing measurable in eight weeks.

The table breaks it down per format.

The participants were trained men, and it ran for eight weeks. Untrained athletes usually have more to gain; elite endurance athletes have less.

So read this as a direction, not as your expected percentage.

What does a 4x4 session look like exactly?

Ten minutes of easy running, then four blocks of four minutes in which your heart rate climbs to 90 to 95 percent of your maximum, with three minutes of walking or very easy jogging between them. Finish with five minutes of cool-down. The whole session runs about 35 minutes, of which 16 minutes are real work.

Two to three times a week is enough.

The protocol comes from researchers at the Norwegian university NTNU in Trondheim, which is why it is nicknamed the Norwegian 4x4. You can run, cycle or row it, as long as your heart rate gets high enough and stays there.

Mind the recovery blocks. Those three minutes are not a bonus but part of the dose: without recovery you will not hold pace in the fourth interval.

Why does almost everyone blow the fourth interval?

Because the first one starts too hard. Your heart rate needs roughly ninety seconds to reach 90 percent, so anyone leaving at top speed buys that speed with their last two blocks. The goal is not four maximum efforts, but four identical ones.

A concrete reference point helps.

Say you have a maximum heart rate of around 185. Your target band then runs from about 167 to 176. Run the first four minutes at 182 and blocks three and four will probably hang below 165, which is exactly the zone that produced nothing in the table above.

That maximum heart rate is usually an estimate, by the way, and often a poor one. Why that is sits in why your heart rate zones are probably wrong.

Why does your VO2max not move even when you train well?

Sometimes the brake is not your training but your oxygen transport. Your heart can pump more blood after eight weeks of intervals, but if that blood carries little oxygen, your maximum uptake changes little. Iron and haemoglobin sit at exactly that point in the chain.

This is the part almost every training article skips.

Burden and colleagues pooled seventeen studies in endurance athletes with low iron stores but no anaemia. Iron treatment improved iron status substantially and had a moderate effect on VO2max, with an effect size of 0.61 (95% CI 0.40 to 0.82) (PMID 25361786). That applied to athletes with a deficiency, not to everyone.

A flat line after eight weeks of serious training is therefore a signal, not a failure.

Which values belong to that, and how to read them next to your training data, sits in cardio fitness and your blood. For endurance athletes, ferritin is the value that drops first most often.

How much easy training do you still need?

More than the table above suggests. Easy distance runs did not raise VO2max in those eight weeks, but they build the base that lets you handle the intervals: more capillaries, more mitochondria, better fat oxidation. Without that base you will not sustain two hard sessions a week.

Think of it as the difference between the ceiling and the floor.

Joyner and Coyle described endurance performance as the interplay of VO2max, lactate threshold and efficiency (PMID 17901124). Intervals mostly lift the ceiling; easy kilometres mostly lift the threshold and the efficiency. You need both.

The Dutch Gezondheidsraad holds 150 minutes of moderately intensive activity per week in its physical activity guidelines, plus muscle-strengthening work twice a week. That is the health floor, with your training plan sitting on top of it.

How much rest belongs between it all sits in when to build in a deload week.

What do you do over the next eight weeks?

Put two 4x4 sessions a week in your plan, keep the rest easy, and measure your starting point before you begin. Without a baseline you will not know in eight weeks whether that 7 percent showed up for you too. How to record that baseline sits in measuring your VO2max.

My suggestion: note the average heart rate of block four each session, not block one.

If your line stays flat after eight weeks while you are finishing the sessions, your blood is a logical next place to look. Iron, haemoglobin, thyroid and inflammation markers sit together in InsideTracker. What a good outcome for your age would be sits in what is a good VO2max.

Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.

References

• Helgerud J, Hoydal K, Wang E, et al. Aerobic high-intensity intervals improve VO2max more than moderate training. Medicine and Science in Sports and Exercise, 2007;39(4):665-71. PMID 17414804.
• Burden RJ, Morton K, Richards T, Whyte GP, Pedlar CR. Is iron treatment beneficial in iron-deficient but non-anaemic endurance athletes? A systematic review and meta-analysis. British Journal of Sports Medicine, 2015;49(21):1389-97. PMID 25361786.
• Joyner MJ, Coyle EF. Endurance exercise performance: the physiology of champions. The Journal of Physiology, 2008;586(1):35-44. PMID 17901124.
• Gezondheidsraad. Physical activity guidelines.