But they also have a very serious mission. And it's especially important for one South Philadelphia woman.
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When 33-year-old Sarah Happy started with her trainer, she wanted to stick to the gym.
"I said, you know, I love working out, but I hate running, so we're not going to to that," she says with a chuckle.
But Cyrena Chang Paulin of the Sporting Club at the Bellevue encouraged Sarah to run anyway.
And now she's hooked.
This weekend, Sarah will run and walk her first half-marathon, the Philadelphia Rock'N'Roll Half Marathon.
She's now a Runner for Research, raising money for the American Association for Cancer Research, the race's charity partner.
Sarah's first encounter with cancer came just after college.
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"I could feel something in my arm, under my arm, and I went to the doctor," she says
The diagnosis was lymphoma.
"I had tumors in my chest cavity, and there was a shadow over my heart from the cancer," recalls Sarah. "Everything in my life changed."
After 6 months of chemo and 2 months of radiation, Sarah was cancer-free - until a routine Pap test a year later.
She recounts, "They're calling me and saying they want a biopsy, they're saying there's these cancer cells and we have to remove them."
It took 2 operations, but Sarah beat cervical cancer and she recently got married.
This 2-time survivor says having doctors with access to the latest research saved her life, so she hopes other runners will join the race, too.
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"You can get involved with not only something you love, but something that's going to benefit a lot of people," she remembers.
And along with that, the AACR says the music keeps runners going.
"All of a sudden, you see this blue band or a soul band or a rock'n'roll band - it's fantastic," says AACR executive director Mitch Stoller.
Here in Philadelphia, there's actually a whole weekend of events, including a fitness expo on Friday and Saturday. The 5K and 10K races are on Saturday and the half-marathon is Sunday.
Online registration is closed, however, runners can register for the 5K and 10K at the expo on Friday or for the half-marathon at the expo Friday and Saturday.
For more information on the 2017 Philadelphia Rock'N'Roll Half-Marathon, CLICK HERE.