British running is booming.
More than 2 million people aged 14 and over take part in athletics for at least 30 minutes a week.
Everyone from OAPs to astronauts now run marathons.
This can only be a good thing surely? Or is it? Could too much exercise actually be harming us?
Everyone's at it
There are now more races and runners than ever.
One million extra races were run in 2015 compared to the previous year.
And running isn't looking so lonely either. It's the fastest-growing participatory sport in the country.
Marathons are booming worldwide. Between 2009 to 2014 there was a 13% increase in marathon running with women picking up faster (26% increase) than men (8% increase).
We love marathons in the UK. (Although, ahem, we are the second slowest nation in Europe just ahead of Greece).
A record total of 247,069 people entered the ballot for the 2016 London Marathon in April.
Last year the oldest runner was 90 and this year even astronaut Tim Peake will be running the London marathon from the International Space Station.
Elite athletes live longer
Government guidelines suggest adults should be doing 150 minutes (2½ hours) of moderate intensity activity every week. And we should aim to be active daily.
But Prof Alejandro Lucia, an expert in the health of elite athletes, believes we should be doing much more than that.
He believes 450 minutes (7½ hours) a week would be ideal.
"Exercise is the only medical intervention [that] benefits most tissues in the body," he told Trust Me, I'm a Doctor's Michael Mosley.
An inactive lifestyle can lead to many health problems like diabetes, osteoporosis, stroke and heart disease.
But beyond that exercise may even help keep us stay younger and more alert.
"There's growing evidence that exercise prevents, to some extent, the risk of cognitive decline with aging," says Prof Lucia.
It is even an antidepressant.
Exercise also reduces the risk of some diseases like colon and breast cancer.
A new ongoing clinical trial is exploring whether running could be offered on the NHS as a cure for cancer.
And elite athletes live longer than the general population.
Trust Me, I'm A Doctor is on BBC Two at 21:00 GMT on Wednesday night - or later on BBC iPlayer