When Kristen Horler had her first child, she, like many new mothers, found that the time demands of parenting made it difficult to exercise. The only workout options open to her were to hire an expensive personal trainer or call a babysitter each time she wanted to go to the gym. Luckily, Horler wasn't just a mom—she was also a group fitness instructor, personal trainer, and triathlete. She soon devised Baby boot camp, a stroller-fitness program that lets new moms and mothers to be engage in challenging workouts while interacting with their babies. StrollFit, the camp's most popular class, leads women through cardio drills, strength training, and gentle stretching routines, ending it all with an intense ab workout designed to whittle down baby weight and redefine the meaning of "tummy time." They also host Strollga, a yoga-inspired fitness class that uses strollers as props, and even lead an eight-week 5K training program.