What is a good cardio fitness score by age?

Apple Watch classifies Cardio Fitness (VO2 max) into four tiers: Low, Below Average, Above Average, and High. For men aged 30–39, 'Above Average' begins at approximately 40 ml/kg/min and 'High' at approximately 48 ml/kg/min. For women in the same age range, 'Above Average' begins around 34 ml/kg/min. These thresholds shift with age — the same VO2 max that ranks you 'Above Average' at 40 would rank you 'High' at 60. The ACSM classifies VO2 max of 33–36 ml/kg/min as 'Good' for men aged 40–49 and 27–30 ml/kg/min as 'Good' for women in the same range.

What is Cardio Fitness on Apple Watch?

Apple Watch's Cardio Fitness is its estimate of your VO2 max — the maximum amount of oxygen your body can use during intense exercise, expressed in milliliters of oxygen per kilogram of body weight per minute (ml/kg/min). Apple estimates this using heart rate data during outdoor walks, runs, and hikes. The estimate updates automatically and is classified into four tiers (Low, Below Average, Above Average, High) relative to your age and sex. For a full explanation of how Apple calculates these tiers, see the dedicated guide on cardio fitness on Apple Watch.

How fast does VO2 max decline with age?

VO2 max declines approximately 10% per decade from your mid-20s onward in sedentary individuals. This works out to roughly 1% per year. In active individuals who maintain consistent aerobic training, the decline is closer to 5–7% per decade — roughly half the rate. The good news: starting aerobic training at any age slows this decline significantly, and previously sedentary adults can improve their VO2 max by 10–25% within 3–6 months of structured training, moving up one or more fitness categories.

Can I improve my cardio fitness score on Apple Watch?

Yes. Apple Watch's Cardio Fitness (VO2 max estimate) responds to actual fitness improvements over weeks to months. The most effective training strategies are consistent Zone 2 aerobic exercise (3–5 sessions of 30–60 minutes per week at 50–70% of max heart rate) and one to two high-intensity interval sessions per week. Research shows that combining moderate aerobic volume with periodic high-intensity work produces the fastest VO2 max gains. See the guide on how to improve cardio fitness on Apple Watch for a structured protocol.

Why does my Apple Watch Cardio Fitness score seem low?

Several factors can cause Apple Watch to underestimate your VO2 max. The most common are: not taking outdoor walks or runs (the metric only updates during these activities), elevated resting heart rate from illness, poor sleep, or high stress, and high body weight relative to cardiovascular capacity (VO2 max is expressed per kilogram). The estimate also takes several weeks to stabilize — a new Apple Watch user may see a gradually improving score as the algorithm accumulates data. If you suspect your score is inaccurate, ensure you are doing regular outdoor workouts and check that heart rate sensors are reading correctly.

Cardio Fitness by Age: VO2 Max Norms and Apple Watch Tier Guide

Quick answer

Cardio fitness (VO2 max) peaks in your mid-20s and declines roughly 10% per decade in sedentary individuals — but only 5–7% per decade with consistent aerobic training. For men aged 30–39, a VO2 max of 37–41 ml/kg/min is "Good" (ACSM); for women it is 31–34 ml/kg/min. Apple Watch's Cardio Fitness tiers (Low / Below Average / Above Average / High) are calibrated to these age-sex norms, so the threshold to reach "High" drops with age. A 2018 cohort study in JAMA Network Open found that being in the lowest fitness quintile carries a 5-fold higher all-cause mortality risk (HR ≈ 5.04) compared with elite fitness — a larger risk-factor association than smoking (HR ≈ 1.41), diabetes, or hypertension. (Mandsager et al., JAMA Netw Open, 2018)

Cardio fitness — your body's maximum aerobic capacity, measured as VO2 max — is one of the strongest objective predictors of long-term health and longevity. Apple Watch surfaces this as your "Cardio Fitness" score under the Heart section of the Health app, classifying it into four tiers relative to your age and sex. Understanding where you fall on the spectrum and what drives the numbers at each age can help you make smarter training decisions for the next decade.

For a complete breakdown of VO2 max norms across all ages and fitness levels with full ACSM tables, see VO2 max by age: ACSM norms for men and women. This page focuses specifically on the cardio fitness context, Apple Watch tier thresholds, and age-related trajectory.

Cardio Fitness (VO2 Max) Norms by Age

The table below shows VO2 max ranges by ACSM fitness classification for men and women across six age groups. These norms are broadly comparable to the age- and sex-adjusted population framework behind Apple Watch Cardio Fitness tiers, though Apple's exact thresholds are not fully public. Values are in ml/kg/min.

VO2 Max by Age — Men (ml/kg/min)

Age	Poor	Fair	Good	Excellent	Superior
20–29	<32	32–37	38–43	44–50	>50
30–39	<30	30–35	36–41	42–48	>48
40–49	<27	27–32	33–38	39–44	>44
50–59	<24	24–28	29–34	35–40	>40
60–69	<21	21–24	25–29	30–36	>36
70+	<18	18–22	23–27	28–33	>33

Source: ACSM fitness classifications (American College of Sports Medicine). Values are approximate — the published ACSM tables use percentile bands that vary by source edition.

VO2 Max by Age — Women (ml/kg/min)

Age	Poor	Fair	Good	Excellent	Superior
20–29	<27	27–31	32–36	37–41	>41
30–39	<25	25–29	30–34	35–39	>39
40–49	<22	22–26	27–31	32–36	>36
50–59	<20	20–23	24–28	29–33	>33
60–69	<17	17–20	21–24	25–30	>30
70+	<15	15–18	19–22	23–27	>27

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Women's VO2 max values are approximately 10–15% lower than men's at every age, primarily due to lower average hemoglobin concentration and smaller heart size relative to body mass. This is a normal physiological difference, not a performance gap that can be fully closed by training.

Apple Watch Cardio Fitness Tiers by Age

Apple Watch classifies your VO2 max estimate into four tiers — Low, Below Average, Above Average, and High — relative to your age and sex. The thresholds for each tier shift with age: the VO2 max that earns a "High" classification at 60 would be "Below Average" at 25. For the exact threshold values Apple uses and a detailed explanation of what each tier means, see cardio fitness on Apple Watch explained.

Apple Watch Cardio Fitness Tier Approximations — Men (ml/kg/min)

Age	Low	Below Average	Above Average	High
20–29	<33	33–39	40–47	≥48
30–39	<31	31–39	40–47	≥48
40–49	<28	28–35	36–43	≥44
50–59	<25	25–30	31–38	≥39
60–69	<22	22–26	27–33	≥34
70+	<19	19–22	23–28	≥29

Apple Watch tier thresholds are approximations based on ACSM population norms. Apple does not publish exact threshold values. Tiers for women are approximately 5–8 ml/kg/min lower than the values shown for men at each age group.

Why Cardio Fitness Matters More Than Most Metrics

VO2 max is not just a fitness metric — it is one of the strongest predictors of long-term health and longevity available without clinical testing. A 2018 cohort study in JAMA Network Open followed over 122,000 patients and found that being in the lowest cardiorespiratory fitness quintile carries a 5-fold higher all-cause mortality risk (HR ≈ 5.04) compared with elite fitness — a larger risk-factor association than smoking (HR ≈ 1.41), diabetes, or hypertension. In other words, low cardiorespiratory fitness as a risk factor is more strongly associated with mortality than smoking as a risk factor. [Mandsager et al., JAMA Netw Open, 2018]

This finding holds across ages — improving cardiorespiratory fitness in your 40s, 50s, and 60s still delivers substantial health benefits. The AHA has recognized cardiorespiratory fitness as a clinical vital sign, recommending that physicians assess and track it alongside traditional cardiovascular risk factors.

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How Cardio Fitness Changes with Age

The 10% Per Decade Rule

In sedentary individuals, VO2 max declines roughly 10% per decade from the mid-20s onward — approximately 1% per year. The mechanisms are well understood: maximum heart rate declines with age (roughly 1 beat per minute per year), cardiac output decreases, and the muscles' ability to extract and use oxygen also diminishes. By age 65, a sedentary individual may have a VO2 max only 40–50% of what it was at age 25.

Training Slows the Decline

Adults who maintain consistent aerobic exercise experience a decline of only 5–7% per decade — roughly half the rate of sedentary peers. Masters athletes (competitive older athletes) who maintain high training volumes show even smaller declines, with some retaining VO2 max values in their 60s that rival those of sedentary 30-year-olds. The key insight is that most of the age-related decline in VO2 max attributed to "aging" is actually the result of reduced training volume — and much of it is reversible.

Trainability at Every Age

Cardiorespiratory fitness remains highly trainable well into later life. Research consistently shows that previously sedentary adults in their 50s, 60s, and even 70s can improve VO2 max by 10–25% within 3–6 months of structured aerobic training. This improvement translates directly to higher Apple Watch Cardio Fitness scores and, more importantly, to measurably reduced cardiovascular disease risk and improved daily function.

How to Improve Your Cardio Fitness Score

Build an Aerobic Base with Zone 2 Training

Zone 2 training — sustained effort at 50–70% of max heart rate — is the cornerstone of VO2 max development. This intensity improves mitochondrial density in muscle cells, increases stroke volume (the amount of blood the heart pumps per beat), and builds the aerobic infrastructure that supports all higher-intensity work. Aim for 3–5 sessions of 30–60 minutes per week. See the how to improve cardio fitness on Apple Watch guide for a structured protocol with progression.

Add High-Intensity Intervals

One to two high-intensity interval sessions per week (e.g., 4–6 intervals of 3–4 minutes at 85–95% of max heart rate with equal recovery) produce the largest acute improvements in VO2 max. HIIT works by pushing cardiac output near its maximum, forcing adaptations in heart function and oxygen delivery. The combination of high aerobic volume (Zone 2) plus periodic high-intensity stress is more effective than either alone for improving VO2 max and maintaining Cardio Fitness scores.

Consistency Over Months, Not Weeks

VO2 max improvements are slow by nature — they require structural adaptations in the heart, lungs, blood, and muscles that take weeks to months to develop. Most individuals see meaningful score changes after 6–12 weeks of consistent training, with larger gains accumulating over 6–12 months. Tracking your Cardio Fitness score trend rather than single values is more informative — look for a 3-month trajectory, not week-to-week fluctuations.

Key Takeaways

VO2 max declines ~10% per decade without training, ~5–7% with consistent aerobic exercise
Apple Watch Cardio Fitness tiers are age-calibrated — compare your score to your age group, not a universal standard
Moving from "Low" to "Below Average" or higher is associated with substantially lower mortality risk at any age
Zone 2 training (3–5x/week) plus 1–2 HIIT sessions produces the fastest VO2 max gains
VO2 max remains trainable in your 50s, 60s, and 70s — a meaningful portion of the decline is modifiable
For full ACSM VO2 max tables and percentile detail, see VO2 max by age

Your Cardio Fitness score is one of the most actionable health metrics your Apple Watch gives you. Unlike resting heart rate or HRV — which fluctuate daily — VO2 max trends slowly and reflects genuine, lasting adaptations in cardiovascular capacity. Track it over months, train consistently in the aerobic zones, and use the tier improvement as a concrete marker of health progress at any age.