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  • Writer's pictureNick Allen

Increasing VO2 max with Zone 5 training

A little over a year ago, we posted a graph on Instagram highlighting the fact that people with “low” cardiorespiratory fitness have around a 5x higher risk of mortality than those with “elite” cardiorespiratory fitness. The study that produced these data used VO2 max, or the maximal amount of oxygen an individual can utilize under exertion, to categorize cardiorespiratory fitness. If VO2 max is such an excellent predictor of health risk, it’s essential that we know how to increase it and maintain it at a high level.

You may recall that there are 5-7 metabolic zones, depending on who you talk to. In the six-zone model we generally follow (Figure 1), the two zones we try and prioritize are Zone 2 (aerobic exercise in which you should be able to hold a conversation) and Zone 5 (anaerobic efforts that represent the highest intensity you can hold for a few minutes). While VO2 max is measured with a maximal physical effort, the first step to increasing your VO2 max is actually having a good low-intensity, aerobic base. This is where Zone 2 training comes in, as we’ve discussed previously.

Figure 1: The six metabolic zones defined by Dr. Inigo San Millan (photo courtesy of

To build on that strong base from Zone 2, you’ll then want to turn to near-maximal efforts — what we consider Zone 5 training. You don’t need a ton of time in this zone, but you should aim to train it at least once a week. Interval training is a great way to accomplish this, and we usually do cycles of 4 minutes on, 4 minutes off. This seems to be the optimal timing for improving VO2 max, but sometimes I’ll do shorter intervals just to get more of a “sprint” feel. In reality, your body can only hold a true “all-out” effort for a few seconds.

Unlike Zone 2, where it’s essential to choose a form of exercise where you can remain at a stable exertion level, the modality for Zone 5 is rather irrelevant. Any exercise where you can give a near-maximal effort for a few minutes — treadmill, bike, rower, stair climber — should work just fine. Recently, I’ve been opting for a stationary bike with a power meter, so I can use my power output as motivation to keep pushing and set new “high scores.”

Again, you don’t have to spend a lot of time in Zone 5 to see a significant impact. Whereas we generally aim for 3+ hours per week in Zone 2, 15-20 minutes per week of high intensity work at Zone 5 can be enough to help boost your VO2 max. This also makes it a great option for days where you don’t have time for an extended Zone 2 aerobic session. If you want to improve VO2 max and reduce disease risk to the greatest extent, however, make sure that you find time for both types of training.


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