Lance Armstrong at the "Planet in Peril" after party at the Roosevelt Hotel in hollywood, CA. on October 17, 2007.
Lester Cohen/WireImage.com

And he's off! Lance Armstrong is gearing up for the NYC marathon on November 4.

"It’s going good," Armstrong, 36, told Usmagazine.com of training last night at a Hollywood screening of the documentary Planet in Peril. "I’m running more this year than I did last year. Last week I ran 18 miles.”

The seven-time Tour de France champ — who recently split with fashion designer Tory Burch— tells Us running is harder than cycling because "riding a bike is more efficient and not as hard on the body."

No doubt Armstrong's three children — son Luke, 8, and twins, Isabelle and Grace, 5 (he split with their mom, Kristin Richard, in 2003) — are also giving him a workout these days.

“They are totally into Halloween!" he says. "My girls are going to be The American Dolls. I don’t have a costume yet.”

How do they all chill in his downtime? " We watch Animal Planet, Shark Week, and Planet Earth," he says. "My son was in mourning for like a week when the Crocodile Hunter died.”

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