Miranda Kerr and Heidi Klum

Miranda Kerr and Heidi Klum

For Heidi Klum's Summer Run series, the supermodel and super-mom is running everyday in the sweltering New York City heat, tracking her steps and calories burned for her new AOL website. And she's usually not flying solo—she's running with her celebrity friends. So far, Klum has pounded the pavement with fellow Victoria Secret model Miranda Kerr, Sports Illustrated swimsuit model Brooklyn Decker (with Klum above), and designer Michael Kors (it took her four weeks to talk him into it).

Admit it, it's cute to see Klum and her friends having fun together while getting fit (or rather fitter, they're all in great shape). But what really made me smile this week was my friends' willingness to workout with me. I recently signed up for theTough Mudder Tri-State, a 12-mile obstacle course that features running, wall-climbing, monkey bars, something called underwater tunnels, and more. I'm psyched for the event, it sounds so weird and challenging, and training for it seems like just the thing to get me out of my workout rut of outdoor running only. The event is many months away, but I already want to get started, and my friends have been quite eager to get in on the fun. Two decided to sign up for the course, including my roommate who said he would join me for parkour classes at my (rarely attended) gym. And others have just offered to help me train. I woke up this morning to an email from my friend Lauren full of links to cross-fit and boot camp classes. My friend Raquel even offered to teach me how to swim. (I can successfully not drown, but the arm motion involved in truly strong swimming eludes me.)

Miranda Kerr and Heidi Klum

I've always ran alone, and used exercise as my form of meditation, so I am a bit nervous about losing that time, but I'm more excited that my friends and I are going to try something new together. Plus, studies have shown that exercising with other people makes you feel happier, more likely to keep up the pace, and more likely to lose weight. (Even virtual partners may help.) Oh and grab the BF or hubby too: A Duke University study found that sedentary men were 50 percent more likely to get off the couch for thrice-weekly workouts if their significant other was participating.