Want muscles like Cameron Diaz [1], Jessica Alba [2], or Jessica Biel [3]? 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.

1. Beginner's workout: CrossFit Games champ Mel Ockerby takes us through a simple workout of squats, sit-ups, and push-ups that anyone can try. You probably know how to do these moves already; get the beginner's CrossFit workout here [4].
2. Back to basics: CrossFit is all about basic moves, so here's a good poster workout [5] to try if you're new to CrossFit. Using moves like push-ups, squats, and deadlifts, this workout is an effective one you can do almost anywhere.
3. Outdoor workout: Who needs a gym when the weather's this nice? Brick gym owner and CrossFit coach Jarett Perelmutter shows us a total-body outdoor CrossFit workout that you can do outside; all you need is a park bench. Get the CrossFit bench workout video here [6].
4. Eight-minute workout: CrossFit is all about high-intensity intervals to get results fast. This Tabata workout video [7] from CrossFit trainer Shirley Brown uses 20-second intense intervals of squats and push-ups to whip you into shape in only eight minutes.
5. Kettlebell workout: There's a reason Jessica Alba always looks so strong and sexy: her trainer Yumi Lee introduced the actress to CrossFit. Yumi showed us how to burn major calories with this CrossFit kettlebell video workout [8].