Doutzen Kroes at the Beach in Miami
Kroes:"I used to always box and run, and with boxing, I would build a lot of muscle. After I had my son, I started doing ballet. It makes you long and lean—it’s like the Pilates look. One thing that I’ve always done since I was younger is suck in my stomach. I think that gave me [ab] muscles. I don’t even think about it—like when you sit in a car, use your core to sit up straight. You can work out sitting in a car! I did leg and butt exercises during my pregnancy, but I haven’t done anything since I had my baby because I don’t want to damage my stomach muscles. It’s better to wait a while."