Singer and star of the new film SparkleJordin Sparks certainly set off a few sparks of her own as she graced the cover of Shape magazine in a teeny-weeny bikini. The star toned up and slimmed down by shedding 50 lbs. thanks to circuit training and even Zumba workouts. "When I first started working out, I only had enough stamina to walk," says the singer who struggled with her weight for years. "But now that I'm exercising every day, I can kick it up a notch -- I've even tried CrossFit!" Got an aggressive weight-loss goal? Be inspired by Sparks and try this routine to work your way up to a high-energy fitness regimen.