ST. PAUL, Minn. -- Tens of thousands of runners might still be in recovery mode today after this weekend's Twin Cities Marathon.

That doesn't mean they're not basking in the bliss of finishing a long race. What is "runner's high"? And what happens in our bodies to create it?

It's hard to match the feeling of winning a marathon, but that doesn't mean those still miles from the finish line aren't finding joy.

"I started feeling it about maybe 23, 24 miles into marathon," said runner Jose Perales.

"It was just pure accomplishment and adrenaline that I pushed through to the end," described another runner.

Happiness from running some would describe as a high. Chris Lundstrom, a senior lecturer at University of Minnesota and long distance running coach, has experienced the unique feeling many times. He said "runner's high" is a subjective feeling.

"People describe a sense of euphoria, a feeling of wellbeing after finishing running especially," said Lundstrom.

Do runners need to reach a certain distance to feel the high? One told us she definitely doesn't notice the high in the first few miles, describing that opening stretch as tough.

"That probably has some variability to it, too," said Lundstrom. "I think as a general rule, it's gotta be 20-plus minutes (of running)."

What is happening in the body that creates the high when running?

"The original theory was it was endorphins which our body produces. these and they go throughout our body," said Lundstrom.

Endorphins can help a runner push through the pain that builds at long distances, allowing some to run further than they planned. But Lundstrom said something else is proving to be the cause thanks to new research.

"They've done a lot of research on endocannabinoids, which similar to cannabis have those kinds of effects on the body, but they're produced within our own body," said Lundstrom.

Exercise increases the level of endocannabinoids in the bloodstream, creating a feeling of calmness and euphoria like the effects of THC in marijuana.

"The first time that I ever ran it, (the high) lasted like 2-3 days," said Perales.

Exercise is known to elevate the mood and lessen depression, said Lundstrom.

He adds that runners seem to think the high they feel is unique, however, specifically when finishing the race. That's an accomplishment in its own right, but with bliss as a bonus.

"When you've stopped running, pay attention to how great it feels and that's a real good motivator for getting out there next time," said Lundstrom.

New runners might not feel the high their first few times out. Even experienced runners don't feel it every time, said Lundstrom.