Your Actual Age vs All the Other "Ages" Your Devices Give You
- TTG Staff
- 2 days ago
- 8 min read
You are 45 years old.
Your Tanita scan tells you your Metabolic Age is 37.
Your Garmin tells you your Fitness Age is 40.
Your Oura Ring tells you your Cardiovascular Age is 42.
Your WHOOP tells you your WHOOP Age is 39.
So… how old are you?
45.
The other numbers aren't different versions of your actual age.
They are estimates created by taking particular measurements or health and fitness data, comparing them with reference data, and presenting the result as an age because an age is something most people can easily understand.
That can make these numbers useful.
But it can also make them very easy to misinterpret.
A Metabolic Age of 35 doesn't mean your entire body is biologically 35.
A Fitness Age of 30 doesn't mean you've somehow reversed ageing.
And two different devices giving you completely different ages doesn't necessarily mean one of them is wrong.
They're often measuring completely different things.
So let's look at what these numbers actually mean.
First: Your Chronological Age
This is the easy one.
Your chronological age is how long you've been alive.
If you were born 45 years ago, you're 45.
Unlike the other numbers we're about to discuss, this isn't an estimate or an algorithm.
Everything else is attempting to answer a different question:
How do certain characteristics of your body, fitness or behaviour compare with those typically associated with people of different ages?
And exactly which characteristics are being assessed depends entirely on the device.
Metabolic Age
The Number You'll See on Your Tanita Scan at The Training Ground
If you've completed one of our Tanita body-composition scans at The Training Ground, you've probably noticed your Metabolic Age.
It is one of those numbers that immediately gets people's attention.
If you're 45 and it says 36, you're probably pretty happy.
If you're 35 and it says 47, you probably want to know what went wrong.
But first we need to understand what Tanita is actually calculating.
Tanita describes Metabolic Age as a comparison between your Basal Metabolic Rate (BMR) and the average BMR associated with your chronological age group.
What is BMR?
Your Basal Metabolic Rate is an estimate of the energy your body requires at rest to maintain essential functions such as:
breathing
circulation
maintaining body temperature
organ function
cellular activity.
Even if you spent the entire day lying still, your body would still require a substantial amount of energy simply to keep you alive.
Your body size and composition influence that requirement.
Lean tissue is metabolically active, so factors such as your amount of fat-free mass contribute to your estimated BMR.
Tanita uses information from your body-composition assessment to estimate BMR and then compares that with age-related reference information to produce your Metabolic Age.
So if you're:
Chronological Age: 45
Metabolic Age: 37
that does not mean your body is literally eight years younger.
It means your result is more similar to the metabolic reference Tanita associates with that younger age.
That's still useful information.
It just needs to be interpreted correctly.
How Does the Tanita Know Your Body Composition?
This is another important distinction.
Our Tanita doesn't open you up and physically measure the amount of muscle and fat inside your body.
It uses Bioelectrical Impedance Analysis (BIA).
A very small electrical current travels through the body and the device measures characteristics such as resistance and reactance as that current passes through different tissues.
Combined with information including your:
height
weight
age
sex; and
measured electrical impedance,
the device uses prediction equations to estimate body composition.
Those estimates then contribute to other calculated values.
This creates an important distinction:
Some things are measured. Other things are estimated from those measurements.
Your Metabolic Age sits further along that chain.
It is a calculated comparison derived from estimated physiological information.
That doesn't make it useless.
It simply means we shouldn't treat a Metabolic Age of 37 as though a laboratory has discovered that your body is biologically exactly 37 years old.
Fitness Age
Fitness Age is something you may have seen on devices such as a Garmin watch.
The concept is similar, but what it is assessing is very different.
Garmin uses cardiorespiratory fitness information, including VO₂ max, as an important part of its Fitness Age calculations.
VO₂ max describes your body's ability to take in, transport and use oxygen during intense exercise.
It is one of the most established measures of cardiorespiratory fitness.
Depending on the Garmin device, additional factors used in Fitness Age calculations can include:
vigorous activity
resting heart rate
body-fat percentage; or
BMI when body-fat information isn't available.
The result is then expressed as an age.
If you're:
Chronological Age: 45
Garmin Fitness Age: 38
Garmin isn't telling you every part of your body is equivalent to a 38-year-old.
It's giving you an age-style interpretation of your fitness data.
Cardiovascular Age
Oura takes yet another approach.
Its Cardiovascular Age is designed to compare aspects of your cardiovascular system with age-related expectations.
One of the important concepts here is arterial stiffness.
Healthy arteries aren't completely rigid. Their ability to expand and recoil helps accommodate the pressure created as your heart pumps blood around your body.
Oura uses information derived from its sensors to estimate pulse wave velocity, which is related to arterial stiffness.
It then compares this information with age-related reference information to generate a Cardiovascular Age relative to your chronological age.
So you could theoretically be:
45 years old
with a:
Metabolic Age of 37
Fitness Age of 39
Cardiovascular Age of 43
There's nothing inherently contradictory about those results.
They're looking through different windows.
Vascular Age
You may also encounter the term Vascular Age.
This appears on some smart scales, cardiovascular systems and health platforms.
Like Cardiovascular Age, the general idea is to translate information associated with the condition of your blood vessels into an age-related comparison.
Depending on the system, this may incorporate measures related to arterial stiffness, pulse wave velocity or cardiovascular risk.
Again, the important question isn't simply:
"What's my Vascular Age?"
It's:
"What did this particular device measure to calculate it?"
WHOOP Age
WHOOP has taken the age concept even further through its Healthspan features.
Rather than focusing predominantly on one physiological characteristic, WHOOP Age uses a broader collection of longer-term data.
This can include factors relating to:
sleep duration
sleep consistency
daily steps
time spent in different heart-rate zones
strength training
resting heart rate
VO₂ max; and
lean body mass.
WHOOP then uses this information to produce a physiological-age estimate.
This is quite different from Tanita Metabolic Age.
Your Tanita result is heavily connected to body composition and estimated metabolism.
WHOOP Age attempts to incorporate a much broader picture of your behaviours and fitness characteristics over time.
Same unit.
Different calculation.
Pace of Aging
WHOOP also provides another interesting metric called Pace of Aging.
Instead of simply asking:
"What age does my current health profile resemble?"
Pace of Aging attempts to describe the direction and rate at which that profile is changing.
This distinction is useful.
Think about someone who has spent years:
sleeping poorly
exercising inconsistently
carrying excess body fat
doing very little cardiovascular training; and
doing no resistance training.
They decide to make substantial changes.
Three months later, their calculated physiological age may still not be where they want it.
But the direction of travel could have changed dramatically.
That is an important idea that extends beyond WHOOP.
Where you are today matters.
But so does where you're heading.
What About Biological Age?
This is where things become particularly confusing.
You've probably heard terms such as:
Biological Age
Body Age
Physiological Age
Health Age
Heart Age
These terms can sound much more definitive than they really are.
There is genuine scientific interest in biological ageing, including research examining molecular, cellular and physiological changes associated with ageing.
But there isn't one universally accepted consumer measurement that can simply tell you:
"Your body is biologically 37.4 years old."
Different systems can use completely different inputs.
Some may examine blood biomarkers.
Others may use cardiovascular measurements.
Others may use fitness.
Others may analyse body composition.
Some biological-age research uses molecular markers such as DNA methylation.
So when someone says:
"My biological age is 32."
the next question should be:
According to what?
Because without knowing what was measured and how the result was calculated, the number tells us very little.
How Can All of My "Ages" Be Different?
Imagine you're 45.
You receive the following results:
Measurement | Result |
Chronological Age | 45 |
Tanita Metabolic Age | 37 |
Garmin Fitness Age | 40 |
Oura Cardiovascular Age | 42 |
WHOOP Age | 39 |
Which one is correct?
Potentially all of them, within the context of what each system is designed to estimate.
They're answering different questions.
Tanita: How does your estimated BMR compare with age-related reference values?
Garmin: How does your cardiorespiratory fitness and related fitness information compare?
Oura: How do characteristics associated with your cardiovascular system compare?
WHOOP: What does a broader collection of your fitness, activity, sleep and body-composition
data suggest about your physiological-age profile?
The mistake is assuming they're all trying to measure the same thing.
They aren't.
Three Questions to Ask Whenever a Device Gives You an "Age"
Rather than immediately celebrating or panicking when you see an age score, ask three questions.
1. What is actually being measured?
Is it looking at:
body composition?
BMR?
VO₂ max?
resting heart rate?
arterial stiffness?
sleep?
physical activity?
blood biomarkers?
a combination of several variables?
This tells you what the number can potentially tell you something about.
2. What is it being compared against?
An age score requires a comparison.
That could be population averages, age-specific reference data, risk relationships or a manufacturer's own proprietary model.
The comparison matters.
3. What can I actually do with this information?
This is the most important question.
Because knowing that your Fitness Age is 48 when you're 42 isn't particularly useful unless it changes what you do next.
Is a Younger Age Always Better?
Generally, these systems are designed so that a younger age relative to your chronological age represents a favourable result.
But don't turn this into a competition to produce the lowest possible number.
Instead, improve the characteristics underneath it.
If you want to improve your body composition and metabolic health, that may involve:
regular resistance training
maintaining or building muscle
appropriate energy intake
improving body composition where necessary
regular physical activity.
If you want to improve your cardiorespiratory fitness, that may involve:
aerobic training
appropriate higher-intensity exercise
increasing daily physical activity
improving VO₂ max
consistently training over time.
If you're thinking about healthy ageing more broadly, the picture becomes larger again.
Strength matters.
Muscle matters.
Cardiorespiratory fitness matters.
Body composition matters.
Blood pressure matters.
Sleep matters.
Nutrition matters.
Balance and mobility matter.
And your ability to continue doing the things you want and need to do matters enormously.
No single "Age" score captures all of that.
Look at Trends, Not Just Scores
One of the most useful things we can do with health and fitness measurements is stop obsessing over individual readings and start looking at trends.
This is particularly important with body-composition testing.
Hydration, recent food and fluid intake, exercise, and testing conditions can influence BIA measurements.
That's why we encourage people completing repeat Tanita scans at The Training Ground to test under reasonably consistent conditions.
A single result gives us information.
Repeated measurements give us a trend.
Imagine that over twelve months you:
increase muscle mass
reduce excess body fat
become considerably stronger
improve your VO₂ max
lower your resting heart rate
increase your daily activity; and
improve your cardiovascular fitness.
Those improvements are far more meaningful than being able to say:
"My Metabolic Age dropped six years."
The lower age might be a nice reflection of the progress.
But the progress itself is what matters.
Don't Let an Algorithm Define Your Health
Age-style scores exist partly because they're easy to understand.
Tell someone their estimated VO₂ max has increased from 36 to 42 mL/kg/min and they may not immediately understand what that means.
Tell them their Fitness Age has moved from 48 to 40 and the improvement feels obvious.
That's useful.
It turns complicated physiological information into something relatable.
The danger comes when the simplified score becomes more important than the information underneath it.
At The Training Ground, we're interested in your numbers.
We'll measure them.
We'll track them.
And we'll use them when they help us make better decisions.
But we're far more interested in what those numbers represent.
Are you stronger than you were?
Can you do more work without becoming exhausted?
Are you maintaining muscle as you get older?
Is your cardiovascular fitness improving?
Can you move confidently?
Can you continue doing the things you enjoy?
Are you building a body that is more capable of handling what life asks of it?
You can't stop your chronological age from increasing.
And you don't need to.
The goal isn't to somehow become younger.
The goal as we see it is to become more capable at the age you are, and maintain as much of that capability as possible for the years ahead.
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