The actress insists she's not a fitness fanatic but she loves the way her body feels after a good run - and she likes to set a good health example to her kids.

Plus, she needs to keep running to prepare for her annual half marathon challenge in her native Iowa.

"I run a half marathon every year with Maria, my best friend from my hometown in Iowa," Michelle tells Shape magazine. "I've known her since I was a kid. We usually do races in different cities, so we'll make a weekend out of it.

"It's great because there are days when I have to do an eight-mile run, and I'll get a text from Maria saying, 'I did eight miles! Did you do yours?' Training with her helps motivate and encourage me."

But she doesn't need much of that: "When I'm not shooting, I aim to work out at least three times a week...," she explains. "On shoot days, I start at about five in the morning and don't get home until seven at night, so it's hard to find time for exercise. I throw myself a bone and don't get too worried about it. I know that when I have time again, I can kick it up a notch.

"I get crabby when I don't work out. Just ask my husband! I really depend on exercising to relieve stress. Last week, I was overwhelmed and I thought, 'I need to go for a run or a hike to clear my head'. I had a to-do list that was a mile long, and I didn't know what to tackle first. When I run, it helps put everything into place."

Her healthy outlook on life means she never has to obsess about what she eats.

"I have never liked fruit. To make up for it, I have a green juice every morning, which is totally devoid of fruit but has tons of vitamins from vegetables," she explains. "A typical day of eating for me is eggs or oatmeal for breakfast, soup or salad for lunch, and fish or meat and lots of veggies for dinner.

"I don't have a sweet tooth; I have a savory tooth. There are six or seven cheeses in my fridge at all times. My idea of snacking is putting cheeses on a platter with prosciutto and crackers and sitting in front of it and stuffing my face."