and Josh Duhamel
, there's nothing like a little rivalry to keep things lively – at the gym.
"She's definitely more competitive than [I am]," Duhamel told PEOPLE at Thursday's New York City Reebok RealFlex footwear launch. "But it's all in fun."
He adds: "She's likely to say, 'Let's do one more mile,' and every time she finishes a workout she says, 'The glory is mine!' meaning she actually got up and did it."
But for the Transformers
star, 38, and his Black Eyed Peas singer wife, 36, a friendly dose of competition isn't necessarily a bad thing. Instead, he says, it helps keep their marriage in tip-top shape.
"We motivate each other. She pushes me, and I push her," says Duhamel, who tied the knot
with Fergie in January 2009. "It's something that we've always done for each other, whether it's working out or in our life together. We're compatible in that way."
Keeping fit and eating healthy is actually a Duhamel tradition. "My mother was a P.E. teacher, and she was kind of a fanatic about fitness and nutrition growing up, so it was ingrained in me at a young age," he says. "As I get older, I'm finding out it's not about getting all buffed up and looking good. It's more about staying healthy and flexible and trying to stay athletic."
When he's not hitting the gym, the actor, who was nicknamed
"Josh Dumbbell" as a kid (more as a joke rather than for his exercise routine), does admit to one vice.
"I'm happy to eat fast food, like McDonald's," he said. "Come on, who doesn't eat it? It's all about moderation, and I don't eat it all the time. But it's definitely a guilty pleasure of mine."