VO2 Max Training: What the Mortality Data Show and Which Intervals Raise It

Higher cardiorespiratory fitness (VO2 max) is one of the most consistent predictors of lower mortality in cohort studies, and it can be trained: interval sessions such as 4x4 minutes at 90-95% of maximum heart rate raised it more than easier running in a randomized trial. The mortality findings are associations, not proof of cause. This page is not medical advice.

Not medical advice. Hard intervals are demanding on the heart. If you are new to vigorous exercise or have a health condition, check with a clinician first.

What VO2 max is and how it is measured

VO2 max is the most oxygen your body can use during all-out exercise. Labs measure it directly from breathing gases. The large mortality studies instead estimated fitness from treadmill tests in metabolic equivalents (METs). In the Kodama meta-analysis, 1 MET of extra capacity corresponded to running or jogging about 1 km/h faster. For how VO2 max sits alongside other tests, see the fitness testing guide.

What the mortality studies found

The 2024 overview also pooled the dose-response data: every 1-MET higher level of fitness was associated with an 11% to 17% lower risk of all-cause mortality, depending on the meta-analysis. That is roughly the gain from running about 1 km/h faster on a treadmill test.

Two findings stand out. First, the relationship was graded with no ceiling: the 2018 Cleveland Clinic cohort concluded that “Cardiorespiratory fitness is inversely associated with long-term mortality with no observed upper limit of benefit.” Second, the veterans study found that “Being unfit carried a greater risk than any of the cardiac risk factors examined.”

What these studies cannot show. All are observational. People with high fitness may also be healthier for genetic, social or medical reasons, and the treadmill cohorts were people referred for testing. The 2024 overview rated the certainty of the evidence as very low to moderate. The safest reading: fitness is a strong marker of health, and training it is very likely good for you, but the hazard ratios are not a personal forecast.

What raises VO2 max

Training studies are randomized, so they answer a narrower question with more certainty: what improves the number itself.

• 4x4 intervals: In Helgerud et al., 40 moderately trained men trained 3 days a week for 8 weeks. Groups doing 4 x 4 minutes at 90-95% of maximum heart rate (with 3 minutes active rest) or 15/15-second intervals raised VO2 max more than groups running at 70% or 85% of maximum heart rate, with total work matched.
• Intervals vs. steady training overall: A meta-analysis of 28 studies with 723 adults aged 18 to 45 found large gains from both. Against no-exercise controls, endurance training added 4.9 and intervals 5.5 mL/kg/min, with intervals a possibly small 1.2 mL/kg/min ahead.
• Longer intervals: A 2013 meta-analysis of 37 studies and 334 people found an average VO2 max increase of 0.51 L/min from interval programmes of 6 to 13 weeks, with larger changes in the 9 studies using longer intervals.

Which interval format works best

A 2019 meta-analysis of 53 randomized trials compared interval protocols directly. Against no-exercise controls, even short intervals (30 seconds or less), low volumes (5 minutes or less of hard work) and programmes of 4 weeks or less improved VO2 max. But the larger effects came from:

Only those longer, higher-volume and longer-running protocols beat moderate continuous training head to head. The authors still recommended short, low-volume formats as a time-saving option for the general population. The 4x4 session fits the bigger-effect profile: four 4-minute efforts make 16 minutes of hard work.

Does training it change mortality?

The closest test is the Generation 100 trial in Trondheim, Norway. It randomized 1,567 adults aged 70 to 77 to two weekly sessions of intervals at about 90% of peak heart rate, two weekly sessions of moderate training at about 70%, or simply following national activity guidelines, for five years.

• Overall: mortality did not differ between the supervised training groups combined and the control group.
• Intervals alone: the interval group had a lower-mortality trend (hazard ratio 0.63), but the confidence interval ran from 0.33 to 1.20, so the result is not statistically certain.
• A complication: the control group was already active and chose to do more hard exercise than the moderate group, which narrowed the contrast. Most participants were also healthy at the start: 87.5% reported good overall health.

The authors concluded that combined training “has no effect on all cause mortality compared with recommended physical activity levels”, while noting the trend after intervals. For a healthy, already active older population, the trial does not show that structured intervals add years. It also does not show they are harmful, and the fitness gains themselves are well established.

A practical weekly structure

• One interval session: For example, 4 x 4 minutes hard (breathing heavily, roughly 90-95% of maximum heart rate) with 3 minutes easy between, as in the Helgerud trial.
• Mostly easy volume: Build the rest of the week from moderate work; the zone 2 guide covers how to pace it.
• Progress slowly: Start with fewer or shorter intervals if you are new to hard efforts.
• Retest every few months: Use the same test each time so changes are comparable.

For how cardio fits with strength and stability work over decades, see the centenarian decathlon framework and the exercise and recovery guide.

Limits of the evidence

The interval trials were short (weeks, not years) and mostly in young or middle-aged adults, often men. Treadmill-based METs are estimates, not measured VO2 max. And no trial has shown that raising VO2 max by a given amount lowers mortality by a given amount.