Even if you’re someone who manages to run regularly now, doing so when you’re 80 may seem ambitious.
But, if you’re worried it may take you hours to jog smaller distances as a pensioner, scientists have the perfect solution for you.
Researchers from Yale University have crafted a formula to help runners predict how much they will – or won’t – slow down as they get older.
And physical decline is slower than you might think – without injury or illness, regular runners can expect to get just one per cent slower per year after they turn 40.
The maths does seem to suggest people have hit their peak by 40 and continue to train the same way afterwards, but shows age can be just a number.
Their calculations suggest a runner should actually only be around 40 per cent slower when they’re 75 than they were at the age of 40.
For example, a 40-year-old who can run 5km (3.1 miles) in half an hour should only take 42 minutes to complete the same distance at the age of 75.
Dr Ray Fair and his colleague, Professor Edward Kaplan, worked out the formula based on marathon records among people in different age groups.
Dr Fair told The Times: ‘People don’t slow down that much even in their seventies and while we are roughly twice as slow at 88 as we were at 40, that’s not all that bad.
‘The bottom line is that people are physically capable of running well for longer than we would expect, which is encouraging.
‘Between 40 and 80 years of age, the time it takes someone to complete a run of a set distance only increases by about one per cent per year.’
To work out how much your running might slow down you only need to know your current age, the age you want to find out about, and your current running time.
Each age between 40 and 95 has a factor (all of which are listed in the table at the bottom of this story) to represent it in the calculation.
The factor for the age you’re testing must be divided by the factor for your current age, then that number should be multiplied by your current time.
For example, if you’re 50 and can run 10km (6.2 miles) in an hour, and want to know how fast you’ll be when you’re 80, you should do these sums:
1.5004 (the factor for 80) ÷ 1.1033 (the factor for 50) = 1.35
1.35 x 60 (current time in minutes) = 81
So you could expect to run the same distance in 81 minutes – 1hr 21m.
The calculator does assume a runner has reached their peak by the age of 40 and they continue to train as hard without being seriously injured or having a long illness.
In reality, people would find it harder to stick to losing just one per cent of fitness per year.
And there is a steeper drop when someone reaches 80 – the fall in fitness between ages 80 and 90 is bigger than the entire period between 40 and 80.
But, experts say, the figures show it is possible for people to stave off ageing by trying to keep fit.
A doctor at Imperial College NHS Trust in London, Frank Miskelly, told The Times: ‘Until you hit 80 you should really feel as good as you did when you were 20.
‘A lot of the decline that comes with age is actually due to the psychological approach to it.
‘Older people are often told they need to slow down; sit around more and take fewer “risks”, but those behavioural changes have more of an impact on fitness than age does.
‘If you maintain a good level of exercise there’s no reason you shouldn’t be physically very capable until you’re 80.’
People become weaker as they get older because of a process called sarcopenia, which is when calcium leaks out of proteins inside the muscles.
This then triggers a chain reaction which eventually makes muscles less able to contract, and therefore weaker, a Columbia University study found in 2011.
The risk of disease is also higher and conditions like type 2 diabetes, high blood pressure and weaker breathing muscles can also make people less able.
Dr Fair and Professor Kaplan published their research in the journal The Review of Economics and Statistics.