How Fitness Age Is Calculated

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ملخص

Fitness age estimates how old your cardiovascular system is relative to population norms. A 45-year-old with excellent fitness might have a fitness age of 30, meaning their VO₂ Max (maximal oxygen uptake) matches the population average for a 30-year-old.

The concept was popularised by the NTNU Cardiac Exercise Research Group (CERG) in Norway. This calculator uses the Jackson et al. (1990) non-exercise prediction equation to estimate VO₂ Max, then maps the result to an age using population reference data.

كيف يعمل

Estimate VO₂ Max — using your age, sex, BMI, and physical activity level (Jackson et al. equation)
Optionally refine — if you provide your resting heart rate, the Uth et al. (2004) heart rate ratio method gives a second estimate, which is combined with the first using a harmonic mean
Map to fitness age — your estimated VO₂ Max is compared against population average VO₂ Max values for each age, and the age where your VO₂ Max would be “average” becomes your fitness age
Classify fitness level — your VO₂ Max is also classified against Cooper Institute norms (Very Poor to Superior) for your age and sex

The formulas

Jackson et al. (1990) — non-exercise prediction

VO₂max = 56.363 + 1.921 × PAR − 0.381 × Age − 0.754 × BMI + 10.987 × Gender

Where

PAR= Physical Activity Rating on a 0–7 scale

Age= Chronological age in years

BMI= Body Mass Index (kg/m²)

Gender= 1 for male, 0 for female

This equation was derived from over 2,000 participants and achieves a correlation of R ≈ 0.80 against laboratory VO₂ Max tests, with a standard error of approximately ±5 ml/kg/min.

Uth et al. (2004) — heart rate ratio (optional)

VO₂max = 15.3 × (HRmax ÷ HRrest)

Where

HRmax= Estimated maximum heart rate (208 − 0.7 × Age, from Tanaka et al. 2001)

HRrest= Resting heart rate in bpm

When both estimates are available, they are combined using a harmonic mean: 2 × J × U / (J + U), which gives less weight to outlier estimates.

Physical Activity Rating (PAR) scale

Rating	Description
0	Avoids walking or exertion
1	Walks for pleasure, uses stairs routinely
3	Light activity 1–2 days/week
5	Moderate activity 3–5 days/week
7	Vigorous activity 6–7 days/week, intense

مثال محلول

35-year-old male, 78 kg, 175 cm, moderate activity (PAR=5), resting HR 68 bpm

Calculate BMI

78 ÷ 1.75² = 78 ÷ 3.0625 = 25.47 kg/m²

= 25.47

Jackson VO₂ Max estimate

56.363 + 1.921×5 − 0.381×35 − 0.754×25.47 + 10.987×1 = 44.42

= 44.42 ml/kg/min

Uth VO₂ Max estimate (with resting HR)

MHR = 208 − 0.7×35 = 183.5; VO₂max = 15.3 × (183.5 ÷ 68) = 41.29

= 41.29 ml/kg/min

Combine via harmonic mean

2 × 44.42 × 41.29 ÷ (44.42 + 41.29) = 42.79

= 42.79 ml/kg/min

Map to fitness age

Male avg VO₂max at age 25 is 43.0 — our 42.79 maps to approximately age 26

= Fitness age: 26

Result

Fitness age = 26 (9 years younger than actual age of 35)

شرح المدخلات

Age — your chronological age (18–80)
Sex — biological sex; males have higher average VO₂ Max due to greater haemoglobin levels and cardiac output
Weight and height — used to calculate BMI, which is an input to the Jackson equation
Exercise level — maps to the Physical Activity Rating (PAR) scale. Higher activity → higher predicted VO₂ Max
Resting heart rate (optional) — measured first thing in the morning before getting out of bed. A lower resting HR indicates better cardiovascular fitness. When provided, enables the Uth heart rate ratio method for a more refined estimate.

شرح المخرجات

Fitness age — the age for which your estimated VO₂ Max would be the population average. Lower than your actual age = fitter than average.
Age difference — fitness age minus chronological age. Negative = younger, positive = older.
Estimated VO₂ Max — your predicted maximal oxygen uptake in ml/kg/min. Elite endurance athletes typically score 60–85; sedentary adults 20–40.
Fitness category — your VO₂ Max classified against Cooper Institute norms for your age and sex (Very Poor through Superior).
BMI — your Body Mass Index, shown for context since it affects the VO₂ Max estimate.

Cooper Institute fitness categories (VO₂ Max, ml/kg/min)

Males

Age	Very Poor	Poor	Fair	Good	Excellent	Superior
20–29	below 33.0	33.0–36.4	36.5–42.4	42.5–46.4	46.5–52.4	above 52.4
30–39	below 31.5	31.5–35.4	35.5–40.9	41.0–44.9	45.0–49.4	above 49.4
40–49	below 30.2	30.2–33.5	33.6–38.9	39.0–43.7	43.8–48.0	above 48.0
50–59	below 26.1	26.1–30.9	31.0–35.7	35.8–40.9	41.0–45.3	above 45.3
60+	below 20.5	20.5–26.0	26.1–32.2	32.3–36.4	36.5–44.2	above 44.2

Females

Age	Very Poor	Poor	Fair	Good	Excellent	Superior
20–29	below 23.6	23.6–28.9	29.0–32.9	33.0–36.9	37.0–41.0	above 41.0
30–39	below 22.8	22.8–26.9	27.0–31.4	31.5–35.6	35.7–40.0	above 40.0
40–49	below 21.0	21.0–24.4	24.5–28.9	29.0–32.8	32.9–36.9	above 36.9
50–59	below 20.2	20.2–22.7	22.8–26.9	27.0–31.4	31.5–35.7	above 35.7
60+	below 17.5	17.5–20.1	20.2–24.4	24.5–30.2	30.3–31.4	above 31.4

Source: The Physical Fitness Specialist Certification Manual, The Cooper Institute for Aerobics Research, Dallas TX, revised 1997 (via Heyward 1998).

الافتراضات والقيود

Non-exercise estimate only. The Jackson equation predicts VO₂ Max from questionnaire data with a standard error of ±5 ml/kg/min. A laboratory cardiopulmonary exercise test is the gold standard.
The Uth heart rate ratio (15.3 coefficient) was validated on well-trained men aged 21–51 only. It may overestimate VO₂ Max for women, older adults, and untrained individuals. The calculator mitigates this by blending Uth with the Jackson estimate via harmonic mean.
Population reference data is approximate. The VO₂ Max-to-age mapping uses values derived from ACSM and HUNT study norms, which represent Western populations and may not apply equally to all ethnic groups.
Activity self-assessment is subjective. The PAR scale relies on honest self-reporting, which can introduce bias.
Fitness age is not a clinical diagnosis. It is a motivational tool that contextualises VO₂ Max in an intuitive way.

التحقق

Test case	Input	Expected VO₂ Max	Expected Fitness Age	Source
Active male	35yo M, 78kg, 175cm, PAR=5, RHR=68	42.79	26	Jackson + Uth harmonic mean
Sedentary female	50yo F, 70kg, 165cm, PAR=3	23.69	64	Jackson only
Very fit male	25yo M, 85kg, 180cm, PAR=7, RHR=55	52.23	18 (clamped)	Jackson + Uth harmonic mean

All values verified against manual calculation of the Jackson et al. (1990) and Uth et al. (2004) equations.

Sources

Academic

Jackson et al. (1990) — Non-exercise VO2max predictionaccessed 15 Feb 2026

Academic

Uth et al. (2004) — Heart rate ratio VO2max estimationaccessed 15 Feb 2026

Academic

Tanaka et al. (2001) — Age-predicted maximal heart rateaccessed 15 Feb 2026

Academic

Cooper Institute — VO2max fitness classification normsaccessed 15 Feb 2026

Academic

ACSM Guidelines for Exercise Testing and Prescription (10th ed.)accessed 15 Feb 2026

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fitness-age vo2max cardiovascular exercise heart-rate