By Alexandria Hoff

PHILADELPHIA (CBS) — Thousands of runners in Philadelphia will hopefully get some extra shut-eye tonight. It’s marathon weekend and the big races are just hours away.

The Convention Center welcomed tens of thousands of participants to its health and fitness expo to pick up their runner’s packets.

“There’s something about proving that you can do something that seems impossible to everybody else, especially when you tell all your friends and family. It’s just kind of fun,” Amanda Brown said.

It will be Brown’s first marathon in Philly but seasoned veterans of the run have also arrived with their hardware.

“I was a former Philadelphia resident and I wanted to come back and run the race, so I did then and it just kept coming,” Mark Sullivan said.

Sullivan and Bob Koen are competing in their 26th Philadelphia Marathon.

“There were only 1,500 people at the first one. I don’t even think they had a half-marathon. It just keeps getting better and better,” Koen said.

“In two years we have had a 24% increase in participants,” said Mitch Stoller, the chief philanthropic officer for the American Association for Cancer Research.

The three races over two days benefit cancer research.

“I think they are really starting to understand that there is a cause,” Stoller said. “The AACR is connected to this event and it makes it just a little more special than just participating in any old run.”

Over $256,000 has been raised so far.

An 8K and half-marathon will take place Saturday and the full marathon will happen on Sunday. Some will run all of them.

“A lot of it is a mental game, a lot of it is mental training,” said ultra runner Jesse Keenan.

Keenan says she will complete all three lengths in what’s known as the Freedom Challenge.

“Before you know it you’re finished and eating soft pretzels,” she said.

Alexandria Hoff