Moderate-intensity endurance training raised VO2 max by about 5 mL/kg/min in healthy young and middle-aged adults, roughly a 10% gain. Trials haven't tested zone 2 training on its own.
- Who it's for
- Healthy, inactive adults; gains are smaller for people already fit.
- What to expect
- About 5 mL/kg/min more VO2 max after several weeks of regular training.
- Watch out for
- Some people gain little at low doses; more weekly time can help.
What guidelines say
The American College of Sports Medicine advises most adults to do moderate-intensity cardio for at least 30 minutes on 5 or more days a week, totalling 150 minutes or more. It also offers a vigorous-intensity option of at least 75 minutes a week3Guideline · 2011American College of Sports Medicine position stand. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise.Educating adults about and screening for signs and symptoms of CHD and gradual progression of exercise intensity and volume may reduce the risks of exercise. Consultations with a medical professional and diagnostic exercise testing for CHD are useful when clinically indicated but are not recommended for universal…Med Sci Sports Exerc.
What the studies show
- A review that pooled controlled trials in healthy adults aged 18 to 45 found endurance training raised VO2 max by about 4.9 mL/kg/min compared with no exercise. The true effect could be anywhere from about 3.5 to 6.3. Gains were larger in younger people, longer programs and less fit people2Meta-analysis · 2015Effectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials.Endurance training and HIT both elicit large improvements in the VO2max of healthy, young to middle-aged adults, with the gains in VO2max being greater following HIT when compared with endurance training.Sports Med.
- In people with type 2 diabetes, a review of 9 trials (266 people) found VO2 max rose 11.8% with exercise at 50% to 75% of VO2 max, about 3 to 4 sessions a week for 20 weeks. It fell 1.0% in the comparison group. Harder exercise tended to give bigger gains7Meta-analysis · 2003 · 266 peopleMeta-analysis of the effect of structured exercise training on cardiorespiratory fitness in Type 2 diabetes mellitus.Regular exercise has a statistically and clinically significant effect on VO(2max) in Type 2 diabetic individuals. Higher intensity exercise could have additional benefits on cardiorespiratory fitness and HbA(1c).Diabetologia.
- A review of 353 studies on muscle changes found VO2 max gains were largely set by starting fitness, with larger gains in less fit people. Steady endurance training, high-intensity intervals and sprint intervals raised it to a similar degree1Meta-analysis · 2025 · 5,973 peopleEffects of Exercise Training on Mitochondrial and Capillary Growth in Human Skeletal Muscle: A Systematic Review and Meta-Regression.The magnitude of change in mitochondrial content, capillarization, and VO2max to exercise training is largely determined by the initial fitness level, with greater changes observed in individuals with lower initial fitness. The ability to adapt to exercise training is maintained throughout life, irrespective of sex…Sports Med.
- Higher-intensity training may give a little more. High-intensity intervals beat steady endurance training by about 1.2 mL/kg/min2Meta-analysis · 2015Effectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials.Endurance training and HIT both elicit large improvements in the VO2max of healthy, young to middle-aged adults, with the gains in VO2max being greater following HIT when compared with endurance training.Sports Med. A review of 29 trials also favored intervals4Meta-analysis · 2023Effect of High-Intensity Interval Training vs. Moderate-Intensity Continuous Training on Fat Loss and Cardiorespiratory Fitness in the Young and Middle-Aged a Systematic Review and Meta-Analysis.The effect of HIIT on fat loss and CRF in the young and middle-aged is similar to or better than MICT, which might be influenced by age (18-45 years), complications (obesity), duration (>6 weeks), frequency, and HIIT interval. Despite the clinical significance of the improvement being limited, HIIT appears to be more…Int J Environ Res Public Health. A small trial of 44 men found no clear difference after 8 weeks9Randomized trial · 2019 · 22 peopleEffects of high-intensity interval training compared to moderate-intensity continuous training on maximal oxygen consumption and blood pressure in healthy men: A randomized controlled trial.Results indicated no significant change in VO2max with a low-volume HIIT protocol versus MICT after 24 sessions. In contrast, MICT provided a greater reduction in systolic blood pressure compared to HIIT. The study is registered as a clinical trial via clinicaltrials.gov with identifier number: NCT02288403.Biomedica. These figures compare groups, so one person's gain depends on their starting fitness.
- In a trial of 78 healthy adults, gains rose with training time. Doing 60 to 300 minutes a week for 6 weeks cut the share who didn't respond. Adding 120 more minutes a week brought a gain in everyone who had not responded6Randomized trial · 2017Refuting the myth of non-response to exercise training: 'non-responders' do respond to higher dose of training.001). In conclusion, individual CRF non-response to exercise training is abolished by increasing the dose of exercise and primarily a function of haematological adaptations in oxygen-carrying capacity.J Physiol.
Key studies
| Study | Who | What it found |
|---|
| Review of controlled trials, 20152Meta-analysis · 2015Effectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials.Endurance training and HIT both elicit large improvements in the VO2max of healthy, young to middle-aged adults, with the gains in VO2max being greater following HIT when compared with endurance training.Sports Med | Healthy adults 18 to 45 | Endurance training added about 4.9 mL/kg/min versus no exercise |
| Review of 9 trials, 20037Meta-analysis · 2003 · 266 peopleMeta-analysis of the effect of structured exercise training on cardiorespiratory fitness in Type 2 diabetes mellitus.Regular exercise has a statistically and clinically significant effect on VO(2max) in Type 2 diabetic individuals. Higher intensity exercise could have additional benefits on cardiorespiratory fitness and HbA(1c).Diabetologia | 266 adults with type 2 diabetes | VO2 max up 11.8% after about 20 weeks |
| Review of 353 studies, 20251Meta-analysis · 2025 · 5,973 peopleEffects of Exercise Training on Mitochondrial and Capillary Growth in Human Skeletal Muscle: A Systematic Review and Meta-Regression.The magnitude of change in mitochondrial content, capillarization, and VO2max to exercise training is largely determined by the initial fitness level, with greater changes observed in individuals with lower initial fitness. The ability to adapt to exercise training is maintained throughout life, irrespective of sex…Sports Med | About 5,973 people | Less fit people gained most |
| Trial of 78 people, 20176Randomized trial · 2017Refuting the myth of non-response to exercise training: 'non-responders' do respond to higher dose of training.001). In conclusion, individual CRF non-response to exercise training is abolished by increasing the dose of exercise and primarily a function of haematological adaptations in oxygen-carrying capacity.J Physiol | Healthy adults | More weekly minutes meant fewer non-responders |
| Trial of 44 men, 20199Randomized trial · 2019 · 22 peopleEffects of high-intensity interval training compared to moderate-intensity continuous training on maximal oxygen consumption and blood pressure in healthy men: A randomized controlled trial.Results indicated no significant change in VO2max with a low-volume HIIT protocol versus MICT after 24 sessions. In contrast, MICT provided a greater reduction in systolic blood pressure compared to HIIT. The study is registered as a clinical trial via clinicaltrials.gov with identifier number: NCT02288403.Biomedica | Healthy men 18 to 44 | Intervals and steady training did not differ clearly |
Safety
Gradual increases in intensity and amount may lower the risks of exercise. Screening for heart disease symptoms is advised, though routine testing for everyone isn't recommended3Guideline · 2011American College of Sports Medicine position stand. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise.Educating adults about and screening for signs and symptoms of CHD and gradual progression of exercise intensity and volume may reduce the risks of exercise. Consultations with a medical professional and diagnostic exercise testing for CHD are useful when clinically indicated but are not recommended for universal…Med Sci Sports Exerc.
What we don't know
- How much VO2 max rises from strict zone 2 sessions alone, since the studies grouped all low and moderate steady training together.
- How much people already fit or older can gain.
Written by AI from the studies listed, without review by a clinician, and graded with the GRADE method. It can be wrong, so check the studies it cites. Education, not medical advice.