Ramona Braganza, the celebrity trainer and Gold's Gym ambassador who developed REDBOOK's Wedding Dress Challenge fitness plan, says the number one mistake she sees women make is overdoing it on cardio—just running, running, running on a treadmill at one moderate pace, without changing things up. The key to getting more out of your workouts, says Braganza, is adding interval training—bursts of high-intensity moves—to your routine.