Backstage with Sandy Kenyon: 'Dancing with the Stars' turns 25

NEW YORK (WABC) -- It's season 25 of "Dancing with the Stars," but for the contestants, it's anything but easy. So what's the toughest part, that came without warning?

"How sore you're going to be," actor Frankie Muniz said. "I mean, you're using muscles that you never use."

Nick and Vanessa Lachey, Debbie Gibson, Derek Fisher and more will try to wipe the ballroom floor with the competition.

"The ballroom is a completely different thing," actor Jordan Fisher said. "You have to focus on every section, every limb, every ligament."

Former NFL star Terrell Owens will partner with pro Cheryl Burke this season to battle it out on the dance floor for the coveted Mirror Ball Trophy.

"Your body's just being put in positions you've never been in before," he said.

The former NFL wide receiver began his professional career with the San Francisco 49ers in 1996. Burke took home the Mirror Ball Trophy for two consecutive seasons, 2 and 3, with celebrity partners Drew Lachey and Emmitt Smith.

"Every girl since they've been young has really wanted to be a dancer," professional wrestler Nikki Bella said. "And when you see them dance, you're like, yeah, OK, I wanna do that."

This season will also see the first-ever official fantasy league for the show.

"This is kind of a once-in-a-life opportunity, to get to be taught by, you know, have an experience like this, it's unrea," violinist Lindsey Stirling said. "And he's such a great teacher. I've wanted to do this show for years, so I'm stoked."

Athletes have had success on the show, winning the Mirror Ball Trophy 10 times. NFL running back Rashad Jennings was last season's champion, with former Chicago Cubs catcher and current ESPN commentator David Ross finishing second.

"I have a handful of friends that have done the show before," Jordan Fisher said. "They've been through the ringer, and they've all said the same thing. They've all said, 'If Dancing with the Stars ever approaches you, you have to say yes.'"

Dancing With the Stars airs Mondays at 8 p.m. ET | 7 p.m. CT on ABC, beginning Sept. 18.