By Nicolette Helling & photojournalist John Thain, FOX 21 News

DULUTH - Watching thousands of Grandma's Marathon runners pass you by can be inspiring.

But what does it take to run 26.2 miles?

Being able to run that kind of distance doesn't come with the snap of a finger.

Dr. Ben Nelson is a sports medicine specialist with Saint Mary's Duluth Clinic.

He says the best place to start a running program is at the doctor's office.

"First, I would check with your primary care physician to talk about if running is safe for you," he said. "Make sure you don't have an underlying medical issue that could be harmful with running."

Nelson said people with cardiovascular disease, diabetes or respiratory problems should be especially cautious before starting to run.

But what if you've never run a day in your life?

"If you've never run before, I would recommend alternating between walking and jogging intervals," he said.

A good way to start running is to start slow.

Nelson suggested running three times a week for 20 to 30 minutes and increasing your time and intensity as your body adapts.

He said some discomfort is normal.

"You might notice some more specific pains in the knees and ankles. Those things are very common," Nelson said. "They should go away."

Even if you've never run before, Nelson said after three or four months of training, you could run a 5k.

But before you sign up for a race, make sure you have the right shoes.

Rachael Stack works at the Duluth Running Company and is a self-proclaimed shoe-guru.

She says there is no general answer to what kind of shoe a person should wear; it has to be customized.

"It's extremely important," said Stack. "If you're in the wrong shoe you can have numerous injuries like knee pain, back pain..."

So, can a person who has never run before finish a marathon?

Nelson says yes.

"I think it would probably take a year long commitment in staying in shape through the winter so that you're ready to really begin serious training four or five months before the race," Nelson said.

Stack, who runs cross country and track for the University of Minnesota Duluth, has simple advice for those starting to run. 

"Don't give up," she said. "Once you get into a routine, you will enjoy it."