How Fitness Age Is Calculated

요약

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.

작동 방식

1. Estimate VO₂ Max — using your age, sex, BMI, and physical activity level (Jackson et al. equation)
2. 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
3. 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
4. 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

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)

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

계산 예시

입력값 설명

• 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.

출력값 설명

• 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

Females

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

가정 및 제한사항

• 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.

검증

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