Ashne Lamb says running is like a drug.

"It is something that you get very addicted to and that's why you keep going back for more," Ashne said.

Ashne started running about nine years ago at her local parkrun in Melbourne's northern suburbs, initially as practice for competing in triathlons.

But the 32-year-old enjoyed it so much she stuck to running, gradually building her endurance and feeling happier as a result. 

"Every couple of months you feel so good after a run you think 'Oh, I could actually do a little bit more'," Ashne said.

Ashne started with a 5-kilometre parkrun before racing as far as 56 kilometres.

"So I can do 10 kilometres and then I can do 15 and before you know it you're doing marathons and then ultramarathons."

Admittedly, ultramarathons aren't everyone's cup of tea but a feeling of elation and accomplishment is something everybody can embrace.

Like Ashne, Kate Corner is an ultramarathon runner.

"I don't run fast but I do run far," Kate quips.

Kate, 44, ran as a kid before "life got in the way" and she stopped, but her passion for the activity re-ignited when she moved to Adelaide more than a decade ago and eventually joined her local parkrun: Pakapakanthi in the Adelaide Park Lands.

And like Ashne, Kate keeps coming back to it because she gets that "euphoria".

"I don't know how else to describe it."

Kate says it's often when she's running by herself, over long distances and out in remote bushland that her euphoria peaks.

"And the fact that I'm still running… that's part of what drives that sense of achievement," Kate explains.

"Wow, I'm out here and I'm moving and I've been moving for hours, even though I'm not moving fast."

That almost indescribable feeling that Ashne and Kate are trying to grasp is what many term as the 'runner's high'.

So what is 'runner's high' and how do you get it?

Depending on who you talk to it's quite rare, an "elusive holy grail", according to Professor David Bishop from Victoria University's Institute of Health and Sport.

"It's almost when you forget you're running," explained Professor Bishop, who researches the benefits of exercise and how to get the most from your movement.

"When you start running you'll feel your heart rate increase, your breathing increase and maybe your muscles will hurt a little bit, and you're pounding on the ground."

So that's the feeling — for want of a better word — but what's actually happening at a physiological level?

For a long time the 'runner's high' has been linked to endorphins — that pleasure-inducing group of chemicals made in the body when we're stressed or in pain.

"I'll sound like the classic egghead academic but I don't think we really know (the cause)," Professor Bishop said.

"But the more recent research suggests that they don't actually cross what's called the blood brain barrier.

"So they're running around in your blood but there doesn't really seem a way that they could get into your brain and stimulate this 'runner's high'."

Professor Bishop points to more recent studies showing the 'runner's high' is linked to endocannabinoids — a group of molecules that activate cannabinoid receptors, which are found throughout the body and mainly in the brain.

"So these are the same thing that's in the THC (tetrahydrocannabinol) in marijuana," he explained.

"So maybe it makes sense to call it 'runner's high' from that perspective!

"These molecules can actually cross the blood brain barrier."

However, it's possible, according to Professor Bishop, the 'runner's high' has nothing to do with these substances in the blood at all.

Hitting the track brings more than just 'runner's high'

For many runners, from weekend warriors to ultramarathon runners, hitting that 'runner's high' might seem impossible.

And while it's addictive for Ashne and Kate it's not the only reason to strap on your runners.

"There are lots of mental health benefits to exercise (and) you don't need to achieve the 'runner's high' to get those benefits," Professor Bishop said.

"If you do, it's a nice bonus."

Kate is most in her element running on long trails in nature.

"I don't like listening to music… I just like to run with my own thoughts in my head.

"It helps you narrow down what's really important. You just let the brain go and the body move."

But it's not always about the individual, Ashne explains.

"Sometimes you can go for a run with somebody else and they've achieved a PB (personal best) or they've managed a distance they've never run before and you get that second-hand 'runner's high', you could say, where you've helped somebody else achieve their goal."

Ashne believes if everyone went for a run, the world would be a less stressful place.

"They would probably be less stressed and I definitely wish that more people would just try running."