How to increase your VO2 max, and how to know it moved

What is VO2 max, and what limits it?

VO2 max is the highest rate at which you can take up and use oxygen in an all-out test, usually given in milliliters per kilogram of body weight per minute (mL/kg/min). It is the product of how much blood your heart pumps and how much oxygen your muscles extract, and in trained people delivery, chiefly stroke volume (blood pumped per beat), is usually the larger limit.

So the training that moves it makes the heart pump near its maximum for minutes at a time: in Helgerud and colleagues (2007), stroke volume rose by about 10% after eight weeks of interval training, alongside VO2 max. It is not race performance; economy (the oxygen cost of your pace) and the fraction of VO2 max you can sustain matter as much over 10 kilometers or a marathon. But it sets their ceiling.

How accurate is Apple Watch VO2 max?

Good for trends, rough as a number. Apple Watch estimates VO2 max, shown as Cardio Fitness, from your heart-rate response to outdoor walks, runs and hikes on fairly flat ground, and independent lab comparisons found it tends to read about 4.5 to 6 mL/kg/min below measured VO2 max on average.

Apple's white paper (2021) says an estimate needs an outdoor walk, run or hike on ground under 5% grade, with adequate GPS, heart-rate signal and exertion, and covers 14 to 60 mL/kg/min. Apple validated it against a reference projected from submaximal tests, not a maximal test; hence the independent studies.

Read together, the watch is useful for direction, less so for the absolute number: in Lambe and colleagues (2025), limits of agreement ran from about −6 to +18 mL/kg/min, so one reading could sit far from the lab value. Compare yourself with yourself, same watch and similar conditions, weeks apart. Your friend's lab test is not your rival.

What is the best way to increase VO2 max: intervals or easy running?

Both work, and intervals win by a smaller margin than their reputation suggests. Pooled controlled trials found continuous endurance training and high-intensity intervals each improved VO2 max meaningfully, with intervals showing a possibly small additional benefit. The practical answer is a mix: mostly easy, some hard.

In Milanović and colleagues (2015), 28 studies and 723 participants, continuous training improved VO2 max by 4.9 mL/kg/min over no-exercise controls, intervals by 5.5. Head to head, intervals had "a possibly small beneficial effect" of 1.2 mL/kg/min. Across 37 studies of 6 to 13 weeks of interval training in people under 45, Bacon and colleagues (2013) found an average rise of 0.51 L/min.

Interval length matters. In Helgerud's study of four groups doing the same total work, both interval groups improved more than the easy and threshold groups, and the longer 4×4 (four minutes hard, three minutes active recovery) gained most: 7.2%. More in the Norwegian 4x4 workout.

The easy base still carries the week: it lets you arrive at the hard session able to do it well, and recover. Over nine weeks in 48 well-trained runners, cyclists, triathletes and skiers, Stöggl and Sperlich (2014) compared polarized, threshold, high-intensity and high-volume programs. The polarized group, mostly easy with a little hard, gained most in VO2peak (peak oxygen uptake in a test): 6.8 mL/kg/min, or 11.7%. Mostly-threshold training, the comfortably hard middle, did no better. One study in trained athletes, but it fits the pattern: the middle is useful, not the engine of VO2 max change.

How many VO2 max workouts should I do a week?

One or two, never on consecutive days, with easy running around them. Hard means efforts of roughly two to five minutes at an intensity where you can say only a few words, with recoveries long enough to start the next one well, and everything else easy.

1. 01

   Easy base

   Most runs at an easy, conversational effort: the volume that supports everything.

2. 02

   One long-interval session

   For example 4 × 4 minutes hard with 3 minutes easy jogging between, or 5 × 3 minutes. Warm up for ten minutes first.

3. 03

   Optional second session

   Shorter repeats or hill efforts, at least two days from the first. Drop it in a busy or tired week.

4. 04

   A lighter week

   Every few weeks, cut volume and keep a little intensity. Adaptation shows up when the load comes down.

Run the first minute of each rep by effort: heart rate lags a sudden change in pace, so a rep that feels right but reads low at ninety seconds is usually fine. New to running? Build a few months of easy running first.

How long does it take to increase VO2 max?

In trials, measurable changes usually appear over six to twelve weeks of consistent training, but the size of the change varies enormously between people on identical programs. A flat reading after a few weeks says little; a flat trend over several months of consistent hard sessions is worth a closer look.

The clearest evidence is the HERITAGE Family Study: Bouchard and colleagues (1999) put 481 sedentary adults from 98 families through the same 20-week program. The average gain was about 400 mL/min, but some gained little or nothing and others more than a liter per minute; the maximal heritability estimate of the response was 47%. Your response is partly yours to shape, partly inherited.

A watch estimate can also stall for other reasons: it only reads outdoor walks and runs on fairly flat ground; heat, dehydration and fatigue raise heart rate at a given pace; and body weight is in the denominator, so a weight change alone moves the number. Check pace at the same heart rate on familiar routes too.

Why does VO2 max matter for longevity?

In large observational studies, higher cardiorespiratory fitness is associated with lower all-cause mortality, and the association does not appear to level off at high fitness. These are associations in cohorts, not proof that raising your own number will change your outcome.

In Mandsager and colleagues (2018), 122,007 patients referred for treadmill testing were followed for a median of 8.4 years. Fitness was inversely associated with long-term mortality "with no observed upper limit of benefit"; elite performers had an adjusted hazard ratio of 0.20 compared with the least fit. The cohort was a clinic population, and fitness tracks many other things about a person. More in running for longevity.

How does Gears use VO2 max?

As one input among several, not a score to chase. At setup, your gears can be placed from your Cardio Fitness in Apple Health, among other sources, and every run with heart rate refines them. VO2 max is deliberately left off the Today screen. More on the VO2 max training app.

• Hard (Gear 3) is where VO2 max work happens. Find a run has two training targets for it, VO2 max: long intervals and VO2 max: short intervals, and a Norwegian 4×4.
• The plan keeps hard days rare. Mostly easy running, at most two hard runs a week, never back to back, and a lighter week every fourth week.
• Fitness shows as pace. After runs, a line shows your pace at the same heart rate over time: "Getting fitter shows here first: the same heart rate buys a quicker pace."