VO2 Max After 40: Why It Matters and How to Improve It

By Cristian Serb · Updated April 5, 2026

VO2 max declines with age, and the rate accelerates over time. Cross-sectional data suggest a roughly 10% loss per decade in sedentary adults, though longitudinal studies show the decline speeds up after age 45 (Fleg et al., 2005). By 60, most sedentary people have lost a third of their aerobic capacity. But here's what the research shows: roughly half that decline comes from inactivity, not biology. When you compare master athletes to sedentary adults, the trained group declines at about 5.5% per decade versus 12% — meaning a large share of the loss is preventable and much of it is reversible (Rogers et al., 1990).

If you're over 40 and wondering whether it's too late to improve your VO2 max, the short answer is no. The longer answer is that improving it now may be the single most important thing you can do for your health.

Why VO2 Max Is the Number That Matters Most

VO2 max, the maximum amount of oxygen your body can use during intense exercise, is the strongest predictor of all-cause mortality we have. Stronger than smoking status, blood pressure, or diabetes (Myers et al., 2002; Mandsager et al., 2018).

A study in the Journal of the American College of Cardiology followed 4,137 healthy adults for an average of 24 years and found that each 1 MET increase in cardiorespiratory fitness was associated with (Imboden et al., 2018):

• 11.6% reduction in all-cause mortality
• 16.1% reduction in cardiovascular mortality
• 14.0% reduction in cancer mortality

A separate JACC study tracked 5,107 men over 46 years and found that each unit increase in VO2 max was associated with a 45-day increase in life expectancy (Clausen et al., 2018).

Put simply: fitter people live longer, and VO2 max is the best measure of that fitness.

How Much Decline Is Normal, and How Much Is Preventable

Here's the typical decline in VO2 max by decade, based on comparisons between sedentary and trained populations (Rogers et al., 1990; Fleg et al., 2005):

Sedentary adults lose VO2 max at about 10% per decade on average. Adults who maintain regular training cut that rate roughly in half. The message is clear: staying active doesn't stop the clock, but it slows it dramatically. Women face additional challenges from hormonal changes during perimenopause and menopause — see our VO2 max guide for women for specifics.

The Good News: Older Adults Respond Well to Training

The idea that you can't significantly improve VO2 max after a certain age is a myth. Research shows:

• People in their 60s can increase VO2 max by 19–26% through structured endurance training lasting 9–12 months (Kohrt et al., 1991)
• Previously sedentary individuals can increase VO2 max by 15–17% in 20 weeks of structured training (Bouchard et al., 1999)
• The relative adaptive capacity of older adults is similar to that of younger adults — healthy people aged 60–71 adapt to endurance training to the same relative extent as young people (Kohrt et al., 1991)

Your ceiling may be lower than it was at 25, but the room for improvement is often larger, precisely because there's been more decline to reverse.

What Kind of Training Actually Works

High-intensity interval training (HIIT)

The research is unambiguous: high-intensity intervals are significantly more effective than moderate continuous exercise for improving VO2 max. A 2024 systematic review and meta-analysis in Sports Medicine – Open covering 44 randomized controlled trials confirmed that HIIT significantly improved cardiorespiratory fitness in older adults compared with both other-exercise interventions and non-exercise controls (Liang et al., 2024).

The key is spending time at 90–95% of your maximum heart rate, the zone where your heart operates at peak stroke volume, driving the adaptations that increase VO2 max.

The Norwegian 4x4, tested in older populations

The Norwegian 4x4 protocol was developed at NTNU's Cardiac Exercise Research Group (CERG) and has been studied extensively in older adults, including people with heart disease.

The Generation 100 Study, the world's largest trial examining how older adults should exercise for longevity, followed over 1,500 elderly participants and found that high-intensity interval training produced greater VO2 max improvements than moderate-intensity continuous training (Stensvold et al., 2020).

In a separate trial with heart failure patients, the 4x4 protocol produced remarkable results (Wisløff et al., 2007):

• 46% improvement in peak oxygen uptake
• 35% increase in stroke volume (blood pumped per heartbeat)
• Hearts became more elastic and efficient

The protocol is straightforward: four 4-minute intervals at 90–95% of your max heart rate, separated by 3-minute active recovery periods. Total workout time is about 38 minutes, including warm-up and cooldown.

Other effective protocols

The Norwegian 4x4 isn't the only option. Other interval protocols that work well for VO2 max improvement include:

• HIIT 30/30: 30 seconds hard, 30 seconds easy. Accumulates high-intensity time in smaller, more manageable chunks and is a good starting point if 4-minute intervals feel daunting.
• VO2 Max 3x3: Three 3-minute intervals with recovery periods. Slightly shorter work bouts than the 4x4.
• Tempo runs: Sustained moderate-to-hard effort. Less intense than HIIT but still beneficial, especially as a complement to interval work.

How to Start Safely After 40

1. Get medical clearance

This isn't just a disclaimer. If you're over 40 and haven't been exercising regularly, see your doctor before starting high-intensity training. This is especially important if you have a history of heart disease, high blood pressure, or other cardiovascular risk factors.

2. Build an aerobic base first

Don't jump straight into 90–95% heart rate intervals. Spend 4–6 weeks building a foundation with Zone 2 training (easy, conversational-pace exercise) at least 3 times per week. This prepares your cardiovascular system, strengthens connective tissue, and reduces injury risk.

3. Start with shorter intervals

If you're new to HIIT, begin with 30/30 intervals rather than the full Norwegian 4x4. Thirty seconds of hard effort followed by 30 seconds of recovery is intense but manageable, and it gives you time to learn how your body responds.

4. Use a heart rate monitor

Perceived effort becomes less reliable as we age, and medications like beta blockers can affect heart rate. A heart rate monitor (like Apple Watch) keeps you honest and ensures you're training in the right zone: not too easy, not dangerously hard.

5. Respect recovery

Recovery takes longer as we age. Start with 2 interval sessions per week with at least 48 hours between them. Fill the other days with easy activity like walking, light cycling, or swimming. More is not better when it comes to high-intensity work.

6. Watch for warning signs

Stop immediately if you experience chest pain, dizziness, unusual shortness of breath, or irregular heartbeat during intervals. These warrant medical evaluation before continuing.

What to Expect

With consistent training (2 sessions per week), here's a realistic timeline:

• Weeks 1–2: Sessions feel hard. Heart rate takes time to climb, and recovery between intervals is slow. This is normal.
• Weeks 3–4: You start finding a rhythm. The same pace produces a slightly lower heart rate, or you can sustain a slightly faster pace.
• Weeks 6–8: Measurable improvements begin showing in Apple Watch VO2 max estimates. Resting heart rate may start dropping.
• Weeks 8–12: Significant gains. Many people see a 10–15% improvement in VO2 max. Daily activities feel noticeably easier.

The gains don't stop there. Continued training maintains and builds on these improvements. The key is consistency: even one session per week helps maintain what you've built.

It's Not Too Late

The Norwegian researchers who developed the 4x4 protocol didn't just test it on young athletes. They tested it on elderly heart patients, and it worked. Hearts remodeled. Fitness improved. Quality of life went up.

Whether you're 42 or 72, your cardiovascular system retains a remarkable capacity to adapt. The protocols are the same. The intensity scales to your fitness level because it's based on percentage of your max heart rate, not an absolute pace. What matters is showing up and doing the work.

The Bottom Line

VO2 max is the strongest predictor of how long you'll live, and it declines with age, but most of that decline is driven by inactivity, not inevitable aging. Structured interval training, done safely and consistently, can reverse years of decline. The research supports it. The protocols exist. And your body is more capable of adapting than you think.

To see where you stand, check our VO2 max charts by age and gender. You can estimate your VO2 max with a beep test or Cooper test, or track it with your Apple Watch or Garmin. Use our VO2 max improvement calculator to project how long it will take to reach your target.

Frequently Asked Questions

Can you improve VO2 max after 40?

Yes. Research shows healthy adults aged 60–71 can improve VO2 max by 19–26% with structured endurance training, and the relative gains are similar to those seen in younger adults. If you're 40–50, your potential for improvement is even greater.

How fast does VO2 max decline with age?

In sedentary adults, VO2 max declines roughly 10% per decade on average, with the rate accelerating after age 45. Adults who maintain regular training cut that decline roughly in half, to about 5–6% per decade.

What is the best exercise to improve VO2 max after 40?

High-intensity interval training (HIIT) is significantly more effective than moderate continuous exercise. The Norwegian 4x4 protocol — four 4-minute intervals at 90–95% of your max heart rate — is the most researched HIIT method for VO2 max improvement and has been tested extensively in older adults.

How often should you do HIIT after 40?

Two sessions per week with at least 48 hours between them. Recovery takes longer as we age, and more is not better. Fill the other days with easy Zone 2 activity like walking, light cycling, or swimming.

Is it safe to do high-intensity exercise after 40?

For most people, yes, but get medical clearance first — especially if you've been sedentary or have cardiovascular risk factors. Build an aerobic base for 4–6 weeks before starting intervals, begin with shorter intervals (30/30), and use a heart rate monitor to stay in the right zone.

How long until you see results?

With 2 sessions per week, most people feel subjective improvements (easier breathing, faster recovery) within 2–3 weeks. Measurable VO2 max gains typically appear after 6–8 weeks. Many people see a 10–15% improvement within 12 weeks.

References

1. Fleg JL, Morrell CH, Bos AG, et al. Accelerated longitudinal decline of aerobic capacity in healthy older adults. Circulation. 2005;112(5):674-682. PubMed
2. Rogers MA, Hagberg JM, Martin WH 3rd, et al. Decline in VO2max with aging in master athletes and sedentary men. J Appl Physiol. 1990;68(5):2195-2199. PubMed
3. Myers J, Prakash M, Froelicher V, et al. Exercise capacity and mortality among men referred for exercise testing. N Engl J Med. 2002;346(11):793-801. PubMed
4. Mandsager K, Harb S, Cremer P, et al. Association of cardiorespiratory fitness with long-term mortality among adults undergoing exercise treadmill testing. JAMA Netw Open. 2018;1(6):e183605. PubMed
5. Imboden MT, Harber MP, Whaley MH, et al. Cardiorespiratory fitness and mortality in healthy men and women. J Am Coll Cardiol. 2018;72(19):2283-2292. PubMed
6. Clausen JSR, Marott JL, Holtermann A, et al. Midlife cardiorespiratory fitness and the long-term risk of mortality: 46 years of follow-up. J Am Coll Cardiol. 2018;72(9):987-995. PubMed
7. Kohrt WM, Malley MT, Coggan AR, et al. Effects of gender, age, and fitness level on response of VO2max to training in 60-71 yr olds. J Appl Physiol. 1991;71(5):2004-2011. PubMed
8. Bouchard C, An P, Rice T, et al. Familial aggregation of VO2max response to exercise training: results from the HERITAGE Family Study. J Appl Physiol. 1999;87(3):1003-1008. PubMed
9. Liang W, Wang X, Cheng S, et al. Effects of high-intensity interval training on the parameters related to physical fitness and health of older adults: a systematic review and meta-analysis. Sports Med Open. 2024;10(1):98. PubMed
10. Stensvold D, Viken H, Steinshamn SL, et al. Effect of exercise training for five years on all cause mortality in older adults — the Generation 100 randomised trial. BMJ. 2020;371:m3485. PubMed
11. Wisløff U, Støylen A, Loennechen JP, et al. Superior cardiovascular effect of aerobic interval training versus moderate continuous training in heart failure patients. Circulation. 2007;115(24):3086-3094. PubMed