Why cardiologists call fitness a vital sign
In 2016 the American Heart Association published a scientific statement arguing that cardiorespiratory fitness should be treated as a clinical vital sign and assessed routinely, alongside blood pressure and cholesterol. Their reasoning was blunt: low fitness predicts death at least as strongly as several risk factors clinicians already measure, including smoking, hypertension and high cholesterol, and adding it to standard risk models meaningfully reclassifies people's risk. The statement defined low fitness as an estimated peak VO2 below 21 mL/kg/min for women (below 28 for men).
The dose-response keeps going at the top end too. A 2018 study of 122,007 consecutive adults referred for treadmill testing at the Cleveland Clinic found no upper limit to the benefit: people in the "elite" fitness band (two standard deviations above the age- and sex-specific mean) had roughly 80% lower risk-adjusted all-cause mortality than the least fit group, and still did better than the merely "high" fitness group.
Two honest caveats. These are observational cohorts, so they show association, not proof that raising your number causes you to live longer. And people who test poorly on a treadmill often have illness that has not yet declared itself — some of the signal is fitness reflecting health rather than creating it. That said, the finding has replicated across dozens of cohorts, sexes and countries, and randomised training trials reliably raise VO2 max, so the practical advice is not in doubt even if the exact causal share is.
Does VO2 max really fall faster after menopause?
This is where a lot of midlife health content gets ahead of the evidence, so here is the careful version.
Two things are well established. First, VO2 max declines with age in women — cross-sectional data suggest roughly 0.35 to 0.44 mL/kg/min per year, often summarised as "about 10% per decade," though researchers who study this decline caution that the shorthand can be badly wrong for any individual. Second, the decline is not linear: it accelerates. In the Baltimore Longitudinal Study of Aging (Fleg and colleagues, Circulation, 2005), the fall was roughly 3–6% per decade in adults in their twenties and thirties but more than 20% per decade after age 70.
What is not settled is whether menopause itself adds an independent hit beyond ageing and reduced activity. You will see "12–15% per decade after menopause" quoted confidently online; we could not trace that figure to a peer-reviewed source, and we are not going to repeat it. A 2025 study in Physiological Reports comparing 69 physically active women across premenopausal, late premenopausal, perimenopausal and postmenopausal stages found no differences in peak VO2 or other cardiopulmonary measures — a small, cross-sectional study in fit women, but a real data point against the idea that the hormonal transition inevitably crashes aerobic capacity. Meanwhile, a 2023 review in the Journal of Applied Physiology on midlife and older women recommends starting endurance training before or shortly after menopause to maximise gains, and reports that women who have trained consistently for years or decades have a VO2 max on par with — or better than — much younger sedentary women, with masters runners in their fifties and sixties reaching close to double the VO2 max of non-exercising postmenopausal peers.
The takeaway that survives all of this: the biggest modifiable driver of your aerobic capacity in your 50s is how much you train, not your oestrogen status. That is genuinely good news, because training is something you control. If declining hormones are affecting your energy, sleep or joints enough to derail exercise, that is worth raising with a clinician — see exercise during menopause and menopause and heart health.
How is VO2 max measured, and how wrong can your watch be?
A true VO2 max comes from cardiopulmonary exercise testing (CPET): you exercise to exhaustion on a treadmill or bike while a mask measures the oxygen you inhale and the carbon dioxide you exhale. Everything else is an estimate built on a model.
| Method | How it works | Accuracy | Best used for |
|---|---|---|---|
| Lab CPET with mask | Maximal graded test with breath-by-breath gas analysis | Reference standard | A true number; also detects abnormal heart, lung or blood-pressure responses to exertion |
| Submaximal lab or clinic test | Heart-rate response to a set workload, extrapolated | Estimate; error widens if your max heart rate differs from the age formula or you take heart-rate-affecting medicines | Screening and tracking when CPET is not available |
| Smartwatch estimate (running-based) | Model using pace, heart rate, age, weight and sex | Running-based estimates have landed within roughly 5–10% of lab values in some validation work; a 2025 PLOS One study of about 30 adults found the Apple Watch underestimated by a mean of 6.07 mL/kg/min, with a 13.3% mean absolute percentage error and Bland-Altman limits of agreement spanning −6.1 to +18.3 mL/kg/min | Watching your own trend over months — not comparing yourself with anyone else |
| Non-exercise questionnaire estimate | Age, sex, BMI, resting heart rate, self-reported activity | Population-level estimate only | Risk screening in research and primary care |
| Field tests (1-mile walk, Cooper 12-min) | Time or distance converted by equation | Estimate; depends on pacing effort and motivation | Cheap repeatable benchmarks you can redo every 8–12 weeks |
The practical rule: your watch number is a trend line, not a verdict. Validation cohorts have been small and skewed young and fit, devices are calibrated mainly on running, and accuracy degrades for beginners, for very fit people and for non-running activity. If your watch says 31 and a lab says 26, the watch is not lying to you exactly — it is answering a slightly different question with a wide error bar. A rise of 3 points on your own watch over three months, measured the same way each time, is far more informative than the absolute value.
What is a "good" VO2 max for a woman my age?
Treat the table below as reference, not a grade. These are 50th-percentile values from the FRIEND registry, which pooled maximal treadmill tests from US laboratories in adults without known cardiovascular disease. The registry drew on eight laboratories across eight states, used varying treadmill protocols, and included relatively few women over 70 (fewer than 100 tests in that decade) — so it describes a population, not your personal target.
| Age | 50th percentile (mL/kg/min) | What it roughly means |
|---|---|---|
| 20–29 | 37.6 | Peak decade for most untrained women |
| 30–39 | 30.2 | Decline typically becomes visible |
| 40–49 | 26.7 | The decade where training pays the biggest dividends |
| 50–59 | 23.4 | Median sits only ~2 points above the AHA low-fitness marker for women (21) |
| 60–69 | 20.0 | Daily tasks start costing a larger share of capacity |
| 70–79 | 18.3 | Small sample; interpret loosely |
That 50s row is the reason this metric deserves attention now. The median American woman in her fifties is close to the fitness level the AHA flags as low. Being average here is not reassuring.
What actually raises VO2 max — and how fast?
Here is a finding that deserves more attention than it gets. A 2023 systematic review and meta-analysis looking specifically at women compared moderate-to-vigorous continuous training with high-intensity interval training and found no meaningful difference: continuous training raised VO2 max by about 3.20 mL/kg/min, intervals by about 3.16, with a mean difference of −0.42 (95% CI −1.43 to 0.60). In mixed-sex populations, meta-analyses have often favoured intervals. In women, the two approaches came out even — and what predicted gains better was simply how many sessions were completed.
So the sensible structure is not "intervals or nothing":
- Build the base. Most of your weekly aerobic minutes should be easy enough to hold a conversation — the classic zone 2 cardio approach. This is what builds mitochondrial density and capillary networks, and it is sustainable enough that you actually accumulate volume.
- Add some hard work, once you have a base. One or two harder sessions a week. Longer intervals (roughly 3–4 minutes hard with a similar recovery) may work better than very short bursts for VO2 max, though that is a secondary observation within the trials rather than a settled finding. Hills and brisk stairs count.
- Meet the floor first. The AHA recommends at least 150 minutes a week of moderate aerobic activity or 75 minutes of vigorous activity (or an equivalent mix), plus muscle-strengthening on at least two days, building amount and intensity gradually. Roughly 300 minutes adds further benefit.
- Do not drop strength work. Muscle mass supports the "extraction" end of oxygen use and protects the bone and joint health that lets you keep training. See strength training for women.
Realistic timeline: expect little visible change in the first 3–4 weeks, measurable gains by 8–12 weeks, and most of the achievable improvement over 6–12 months of consistent training. Typical gains in previously sedentary midlife women land in the range of 3–5 mL/kg/min, which is close to a full MET — the same increment associated with 13% lower mortality in the pooled cohort data. Response varies a lot between individuals, and some of that is genetic; the people who gain least from a given programme still gain, and they gain more by training more often. If your number stalls, the usual culprits are too little total volume, too much time in an uncomfortable middle intensity, or under-recovery — not a broken metabolism.
When to see a doctor
Most women can increase easy aerobic activity without any clearance. The caution applies to hard effort. Current ACSM pre-participation screening no longer stratifies everyone by risk factors; it asks three things — are you currently exercising regularly, do you have known cardiovascular, metabolic or kidney disease, and do you have signs or symptoms suggesting it.
Talk to a clinician before starting high-intensity intervals if you:
- have known heart, kidney, or metabolic disease (including type 1 or type 2 diabetes), or have had a cardiac event or procedure
- have been largely inactive and want to jump straight to vigorous training
- get chest discomfort, unusual breathlessness, palpitations, dizziness or fainting with exertion
- have uncontrolled high blood pressure, a known arrhythmia, or a heart murmur that has not been evaluated
- are on medicines that blunt heart rate (such as beta blockers), which also make watch- and formula-based estimates less reliable — do not change any medicine on your own; that is a prescriber's decision
Stop and seek urgent care for chest pressure, pain or tightness; pain radiating to the jaw, neck, back or arm; sudden severe breathlessness; fainting; or an irregular heartbeat that does not settle with rest. In the US, call 911. Women's heart-attack symptoms more often present as nausea, extreme fatigue, back or jaw pain and breathlessness rather than crushing chest pain, which is one reason they get dismissed — read heart attack symptoms in women. If you want a structured look at your overall cardiovascular picture before you start, our heart risk check walks through the standard factors, and exercise after 50 covers safe progression.
The bottom line
VO2 max is one of the few health numbers where the evidence is strong, the trend is unfavourable with age, and the lever is largely in your hands. You do not need a lab test to act on it — the training that raises VO2 max is the same regardless of whether you ever measure it. But if you like data, measure it consistently with one method, ignore cross-person comparisons, and watch the direction of travel over quarters rather than weeks.
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