Short answer
To improve VO2 max, do regular aerobic training and include some high-intensity intervals. In a 2015 meta-analysis of 28 controlled trials, steady endurance training raised VO2max by about 4.9 mL/kg/min and intervals by about 5.5, compared with no exercise. Intervals came out slightly ahead, and a 2021 analysis in middle-aged and older adults found the same. Watch-based VO2max numbers are estimates.
Why VO2 max is worth raising
VO2max is the most oxygen your body can use during hard exercise, and it is the usual measure of aerobic fitness. In a Cleveland Clinic study of 122,007 adults who took a treadmill test (JAMA Network Open, 2018), the least fit had about five times the risk of death of the fittest (hazard ratio 5.04). Smoking carried a hazard ratio of 1.41 in the same analysis.
Two caveats: the study is observational, and it estimated fitness from treadmill performance rather than measuring oxygen use directly.
Intervals vs steady cardio
A 2015 meta-analysis in Sports Medicine pooled 28 controlled trials with 723 healthy adults aged 18 to 45. Compared with no exercise, steady endurance training raised VO2max by 4.9 mL/kg/min and high-intensity intervals by 5.5. Head to head, intervals gave about 1.2 mL/kg/min more.
For adults 40 to 60, a 2021 meta-analysis of 14 studies with 429 middle-aged and older adults found interval training raised VO2max by 2.26 mL/kg/min and moderate continuous training by 1.34, a difference of about 1.1.
What an interval session looked like
The best-known protocol is the 4 x 4 from a 2007 Norwegian trial in 40 moderately trained young men: 4 minutes at 90 to 95% of maximum heart rate, then 3 minutes of active rest at 70%, three days a week for eight weeks. VO2max rose 7.2%, more than with steady training at the same total work.
In people with heart disease, high blood pressure, metabolic syndrome or obesity, a 2014 meta-analysis of 10 studies found intervals raised peak VO2 by 3.03 mL/kg/min more than moderate training. Check with your doctor before starting hard intervals.
Your watch's number is an estimate
The trials above measured VO2max with exercise tests before and after training. Consumer devices estimate it. A 2022 meta-analysis of 14 validation studies found wearables that rely on resting data overestimated VO2max. Exercise-based estimates were accurate on average, but the authors called the error for an individual large.
In a 2024 study of 19 adults, the Apple Watch Series 7 was off from lab-measured VO2max by 15.8% on average. Use a watch to follow your own trend, not to compare yourself with a study.
Related questions
How much can VO2 max improve?
In a 2015 meta-analysis of healthy adults aged 18 to 45, training raised VO2max by about 4.9 to 5.5 mL/kg/min over no exercise. Gains were smaller in a 2021 analysis of middle-aged and older adults, about 1.3 to 2.3 mL/kg/min.
Is zone 2 enough to raise VO2 max?
It helps, but in the meta-analyses we read, interval training raised VO2max a little more than steady moderate training.
Is my Apple Watch VO2 max accurate?
It is an estimate. A 2024 study of 19 adults found an average error of 15.8% against a lab test, so it is better for tracking your own trend.
Read next
Sources
- Milanović et al., Sports Med: HIT vs continuous endurance training for VO2max, meta-analysis (2015)
- Poon et al., J Sports Sci: Interval training vs MICT in middle-aged and older adults, meta-analysis (2021)
- Mandsager et al., JAMA Network Open: Cardiorespiratory fitness and long-term mortality (2018)
- Helgerud et al., Med Sci Sports Exerc: Aerobic high-intensity intervals improve VO2max more than moderate training (2007)
- Molina-Garcia et al., Sports Med: Validity of VO2max estimated by consumer wearables, meta-analysis (2022)
Published 2026-10-07 · Last checked 2026-10-07
Educational content, not medical advice. Made for the United States.