Rx: 30 minutes of weight training followed by 30 minutes of cardio 3x a week, plus 45 to 60 minutes of straight cardio 3x a week. One day of rest.
The great thing about being in your 20s is that your body is so strong, you can get away with abusing it. The bad thing is that you often do, punishing it with late nights and bad eating habits. And you routinely fail to appreciate what you've got. This is the decade of anxiety—frantic exercise, fad diets, the mad pursuit of pinup perfection and self-hatred when you fail to meet it. The fitness challenge of these years: Get over it.
"I tell my young clients, 'Forget looking like Jessica Simpson or Halle Berry, and forget weight; think health,'" says Jeanette Jenkins, 32, a Los Angeles based private trainer who has worked with rapper Queen Latifah and actress Taryn Manning. The mistake many 20-somethings make is simply opting for "endless cardio and crunches," adds Vanessa Carver, 25, a personal trainer at Fitness Quest 10 in San Diego, whose clients include professional ice-skaters and dancers. Lots of cardio is great, she says, especially if you mix it up so you're really pushing the body. But it's weight training that builds muscle definition, not to mention bone density, which will be crucial for staying active later on and preventing osteoporosis. "You've got to lift more than just three or five pounds," she says. "If you can do 10 to 15 repetitions of a weight with no real effort, it's too light. The last four or five reps should be challenging enough that you feel your muscles getting fatigued." And put your mind into it, she says. "Lifting weights while chatting on the cell phone is a joke."