Want muscles like Cameron Diaz, Jessica Alba, or Jessica Biel? You may want to try CrossFit. The workout has many devoted fans, not just incredibly fit celebrities, who love it not only for its scalability — workouts are tailored to your current ability, and the difficulty increases as you get better — but also for the mental challenge that comes from pushing yourself further with each workout.
CrossFit uses simple exercises involving body resistance, gymnastics, aerobics, weight lifting, and other moves, which are done at a high intensity. While the exercises are simple, that doesn't mean you'll be bored — CrossFit is all about mixing up exercises and ramping up difficulty over time so you don't do the same workout twice in a row.