Ever since Gwen Stefani started as the frontwoman of No Doubt, she has not been shy about showing off her rock-solid abs. While she still knows how to rock out, the 42-year-old mom of two admits to Marie Claire that she can't quite train like she used to. "I was definitely swimming upstream," she says, "trying to balance everything that's been going on with having kids and a family. There's no way to do all these things." Now she has a less intense workout regimen, cutting back her gym sessions and opting for Pilates to keep her core tight and toned. Take a cue from Stefani and don't hold yourself to the workout regimens that used to work for you before the days of PTA meetings and carpool. Like everything else in life, let your exercise routine change and evolve with your needs and demands.