Stressing Fitness

Getting fit the P90X way means working out 6-7 days per week, with each workout lasting about 1-1½ hours. And the workouts are so rigorous that you're asked to take a fitness test before ordering the P90X system, to see whether you're up to the challenge.

Each workout is presented in a circuit format, in which you move from exercise to exercise with little rest in between, thus keeping your heart rate up. The strengthening DVDs target certain parts of the body each day: chest and back; then shoulders and arms; legs and back; chest, shoulders, and triceps; and back and biceps. Other DVDs focus on plyometrics (explosive "power" movements), Kenpo kickboxing, cardio fitness, abs/core, yoga, and stretching. 

The P90X system is based on the concept of "muscle confusion," which means varying the workout schedule and introducing new moves so the body never fully adapts. This is similar to the periodization techniques athletes use to get their bodies in top condition.  It also has a basis in science; research suggests that workout programs that offer variation bring greater benefits than those that do not.