Why the direction your aerobic fitness is moving may matter more than you think
Most of us have a handful of health numbers we keep an eye on.
Weight.
Blood pressure.
Cholesterol.
Perhaps our daily step count.
They are all useful pieces of information. But there is another number that receives far less attention outside sport and exercise, despite telling us something fundamental about how well the body is functioning.
Cardiorespiratory fitness.
Or, more specifically, our ability to take in oxygen, transport it around the body and use it to produce energy.
In exercise science this is often expressed as VO₂ max.
The name makes it sound like something designed for cyclists in Lycra or athletes wearing oxygen masks in laboratories.
It isn’t.
Your aerobic fitness influences something much more ordinary.
How hard it feels to walk up a hill.
How quickly you recover after climbing a flight of stairs.
Whether you can keep up with your children or grandchildren.
How easily you tolerate a long day of walking on holiday.
And, increasingly, research is suggesting that it may tell us something important about how well we are likely to age.
What makes a new study published this month particularly interesting is that the researchers didn’t simply ask whether fitter people were healthier.
They asked a different question.
What happens when our fitness changes?
Your Fitness Is Not Fixed
It is easy to think of fitness almost like height.
You are either fit or you aren’t.
Some people have always been runners. Others hated PE at school and decided long ago that cardiovascular exercise simply wasn’t their thing.
But fitness isn’t a fixed characteristic.
It is an adaptation.
Challenge the cardiovascular system regularly and it responds. The heart becomes better at pumping blood. Muscles become better at extracting and using oxygen. Mitochondria, the tiny energy-producing structures inside our cells, adapt to meet the demand being placed upon them.
Stop providing that stimulus and the process can gradually move in the opposite direction.
That means the more useful question may not simply be:
How fit am I?
It may be:
Am I getting fitter or less fit?
That distinction is at the heart of some fascinating new research.
What the New Research Found
Researchers analysed 11,530 adults aged between 40 and 73 from the UK Biobank.
Importantly, their cardiorespiratory fitness wasn’t measured just once.
Participants completed two fitness assessments using a submaximal cycling test, roughly four years apart. Researchers could therefore estimate whether their VO₂ max had improved, remained relatively stable or declined.
They then followed the group for cardiovascular outcomes.
The median follow-up from the original assessment was around 14 years. During that period there were 921 new cardiovascular disease events and 119 cardiovascular deaths.
And this is where things became interesting.
People whose estimated VO₂ max improved by at least 1 mL/kg/min per year had around a 16% lower risk of developing cardiovascular disease compared with those whose fitness remained stable.
Those whose fitness declined by the same amount had around a 33% higher risk.
The association remained even after the researchers accounted for baseline fitness and a range of other factors including physical activity, BMI changes, smoking, diet and genetic predisposition to cardiovascular disease.
There was also an association between increasing fitness and lower cardiovascular mortality, although the number of cardiovascular deaths was much smaller and those figures should therefore be interpreted with appropriate caution.
This was an observational study, so it cannot prove that increasing VO₂ max directly caused the reduction in cardiovascular events.
That’s an important distinction.
But it adds another piece to an already substantial body of evidence suggesting that cardiorespiratory fitness is worth paying attention to.
And perhaps most importantly, it suggests that change itself matters.
You Don’t Have to Start as the Fittest Person in the Room
This is the part of the research I find particularly encouraging.
When people hear about VO₂ max, comparisons usually follow.
What’s a good VO₂ max for my age?
Where do I rank?
How fit should I be at 50?
Those questions can be useful. Age-related norms give us context.
But constantly comparing yourself with somebody who has been running for 30 years isn’t necessarily very helpful.
Imagine two people.
One has always been naturally fit but has gradually stopped training. Their cardiovascular fitness is slowly falling each year.
The other starts from a lower level but begins walking regularly, adds some structured cardiovascular training and gradually improves.
The first person may still score higher today.
But their trajectories are heading in opposite directions.
And trajectory is something we can influence.
That is a far more useful message than simply being told that you should have started exercising 20 years ago.
You cannot change what your fitness was at 35.
You can change what it might be at 55, 65 or 75.
Researchers analysed 11,530 adults aged between 40 and 73 from the UK Biobank.
Importantly, their cardiorespiratory fitness wasn’t measured just once.
Participants completed two fitness assessments using a submaximal cycling test, roughly four years apart. Researchers could therefore estimate whether their VO₂ max had improved, remained relatively stable or declined.
They then followed the group for cardiovascular outcomes.
The median follow-up from the original assessment was around 14 years. During that period there were 921 new cardiovascular disease events and 119 cardiovascular deaths.
And this is where things became interesting.
People whose estimated VO₂ max improved by at least 1 mL/kg/min per year had around a 16% lower risk of developing cardiovascular disease compared with those whose fitness remained stable.
Those whose fitness declined by the same amount had around a 33% higher risk.
The association remained even after the researchers accounted for baseline fitness and a range of other factors including physical activity, BMI changes, smoking, diet and genetic predisposition to cardiovascular disease.
There was also an association between increasing fitness and lower cardiovascular mortality, although the number of cardiovascular deaths was much smaller and those figures should therefore be interpreted with appropriate caution.
This was an observational study, so it cannot prove that increasing VO₂ max directly caused the reduction in cardiovascular events.
That’s an important distinction.
But it adds another piece to an already substantial body of evidence suggesting that cardiorespiratory fitness is worth paying attention to.
And perhaps most importantly, it suggests that change itself matters.
Why Midlife Matters
Another large study published in the Journal of the American College of Cardiology earlier this year gives us another reason to pay attention before old age arrives.
Researchers looked at 24,576 adults whose cardiorespiratory fitness had been measured earlier in life using treadmill testing.
They then examined what happened as those people moved into later life.
Those with higher levels of fitness in midlife were associated with a longer healthspan, fewer chronic diseases and a slightly longer lifespan.
Perhaps the most tangible finding was this:
Across 11 major chronic conditions, disease onset occurred on average at least 1.5 years later in the high-fitness groups compared with the low-fitness groups.
Again, association is not causation.
People with higher fitness may differ from those with lower fitness in many ways.
But taken alongside decades of cardiovascular research, the pattern is becoming difficult to ignore.
Your 40s and 50s are not a waiting room before you need to start worrying about ageing.
They are potentially some of the most valuable years in which to build physical capacity.
This is the part of the research I find particularly encouraging.
When people hear about VO₂ max, comparisons usually follow.
What’s a good VO₂ max for my age?
Where do I rank?
How fit should I be at 50?
Those questions can be useful. Age-related norms give us context.
But constantly comparing yourself with somebody who has been running for 30 years isn’t necessarily very helpful.
Imagine two people.
One has always been naturally fit but has gradually stopped training. Their cardiovascular fitness is slowly falling each year.
The other starts from a lower level but begins walking regularly, adds some structured cardiovascular training and gradually improves.
The first person may still score higher today.
But their trajectories are heading in opposite directions.
And trajectory is something we can influence.
That is a far more useful message than simply being told that you should have started exercising 20 years ago.
You cannot change what your fitness was at 35.
You can change what it might be at 55, 65 or 75.
Researchers analysed 11,530 adults aged between 40 and 73 from the UK Biobank.
Importantly, their cardiorespiratory fitness wasn’t measured just once.
Participants completed two fitness assessments using a submaximal cycling test, roughly four years apart. Researchers could therefore estimate whether their VO₂ max had improved, remained relatively stable or declined.
They then followed the group for cardiovascular outcomes.
The median follow-up from the original assessment was around 14 years. During that period there were 921 new cardiovascular disease events and 119 cardiovascular deaths.
And this is where things became interesting.
People whose estimated VO₂ max improved by at least 1 mL/kg/min per year had around a 16% lower risk of developing cardiovascular disease compared with those whose fitness remained stable.
Those whose fitness declined by the same amount had around a 33% higher risk.
The association remained even after the researchers accounted for baseline fitness and a range of other factors including physical activity, BMI changes, smoking, diet and genetic predisposition to cardiovascular disease.
There was also an association between increasing fitness and lower cardiovascular mortality, although the number of cardiovascular deaths was much smaller and those figures should therefore be interpreted with appropriate caution.
This was an observational study, so it cannot prove that increasing VO₂ max directly caused the reduction in cardiovascular events.
That’s an important distinction.
But it adds another piece to an already substantial body of evidence suggesting that cardiorespiratory fitness is worth paying attention to.
And perhaps most importantly, it suggests that change itself matters.
Think of Fitness as Your Engine
There is a simple way to think about aerobic fitness.
It is the size of your engine.
Imagine that walking quickly up a steep hill requires a certain amount of energy.
If that effort represents 90% of your cardiovascular capacity, the hill feels hard. Your breathing becomes laboured and fatigue arrives quickly.
Increase your capacity and exactly the same hill might now require 60%.
The hill hasn’t changed.
You have.
That extra capacity creates what we might call physiological headroom.
And that headroom becomes increasingly valuable as we get older.
It gives us more capacity for travel, gardening, sport, walking, playing with grandchildren and simply getting through busy days without feeling exhausted.
It may also give us greater reserve when life doesn’t go according to plan.
Illness, surgery and periods of inactivity can all reduce physical capacity. Starting with a bigger engine gives us more to work with.
This is one reason BlueZone places aerobic fitness alongside strength, balance, mobility and power when we think about healthspan. It isn’t simply about endurance sport. It is part of the physical reserve that allows us to remain capable.
Exercise and Fitness Aren’t Quite the Same Thing
There is another distinction worth making.
Physical activity is what you do.
Fitness is how your body has adapted to what you do.
You can record 10,000 steps on a watch.
You can complete three workouts this week.
You can cycle every Sunday.
All of those behaviours are worthwhile.
But the more interesting question is whether they are creating the adaptation you want.
Has your walking pace improved?
Can you cover more distance in the same time?
Does the hill that used to leave you breathless now feel manageable?
Can you run at the same speed with a lower heart rate?
Do you recover more quickly between harder efforts?
Those are signs that the engine may be changing.
This is why measurement can be so useful.
Not because everyone needs to turn exercise into a laboratory experiment.
And certainly not because every workout needs another number attached to it.
But because without an occasional benchmark, it is surprisingly difficult to know whether we are maintaining capacity, gaining it or quietly losing it.
So How Do You Improve Aerobic Fitness?
Fortunately, improving your cardiovascular system doesn’t require every workout to leave you lying on the floor.
In fact, it probably shouldn’t.
A good aerobic programme usually contains different gears.
There is value in steady cardiovascular work: brisk walking, running, cycling, swimming, rowing or any other activity that keeps you moving continuously at a manageable intensity.
This builds the foundation.
You are teaching the body to deliver oxygen efficiently and produce energy for longer periods without excessive fatigue.
Then there is a place for harder work.
Shorter intervals, hills or periods of faster running or cycling can challenge the upper end of the cardiovascular system and help raise the ceiling.
The exact prescription should depend on age, current fitness, training history and health status.
Someone returning to exercise at 68 does not need the same session as a well-trained 42-year-old.
The principle, however, is remarkably similar.
Give the body a reason to adapt. Recover. Then repeat it consistently.
And don’t underestimate ordinary movement.
Walk to the shops.
Take the stairs.
Go out after dinner.
Garden.
Carry things.
Move whenever life gives you the opportunity.
Those activities may not replace structured training when the goal is specifically to improve cardiovascular fitness, but they create an active lifestyle around it.
The combination is powerful.
Measure Something That Can Change
A laboratory VO₂ max test gives us a detailed assessment of cardiorespiratory fitness, but most people don’t need a laboratory every few months.
Well-chosen field tests can also give us a useful benchmark.
The key is consistency.
Use the same test.
Use a similar protocol.
Record the result.
Train.
Then repeat it.
At BlueZone, aerobic fitness is assessed using safe, age-appropriate testing so that it can sit alongside other measures of physical capability such as strength, balance, mobility and power. The aim isn’t to hand somebody a score and send them home.
It is to establish a starting point.
Assess. Improve. Retest.
Because a fitness result only becomes truly useful when it helps you decide what to do next.
Don’t Chase Someone Else’s Number
There is a danger when we start measuring health.
Numbers can quickly become another form of competition.
That isn’t the point.
If you are 63 and beginning exercise again after ten sedentary years, your starting result may not be where you would like it to be.
Fine.
It is information, not a verdict.
The first goal might simply be to stop the decline.
Then improve a little.
Then improve again.
Six months later, perhaps the hill feels easier.
Perhaps you can walk further.
Perhaps your recovery is better.
Perhaps the test result has moved.
That is progress.
The new UK Biobank study is particularly interesting because it shifts our attention away from fitness as a static label and towards fitness as something dynamic.
You aren’t simply fit or unfit.
Your body is adapting all the time.
The question is which direction you are encouraging it to move.
The Number Matters. The Direction Matters More.
We spend a great deal of time worrying about ageing as though it is something that suddenly happens to us.
It isn’t.
Most of the changes we associate with ageing accumulate quietly over decades.
A little less muscle.
A little less fitness.
A little less balance.
A slightly smaller physical world.
And because the decline is gradual, it is remarkably easy not to notice.
Until something that used to feel easy suddenly doesn’t.
That is why I like this research.
It gives us a much more optimistic way to think about the future.
You don’t need perfect health.
You don’t need the VO₂ max of an endurance athlete.
And you don’t have to undo every year of inactivity overnight.
What matters is creating a body that is moving in the right direction.
A little stronger.
A little fitter.
A little more capable.
Then checking occasionally to make sure the plan is actually working.
Because the goal isn’t simply to add more years to life.
It is to arrive at those years with an engine that still allows you to use them.