P90X focuses on muscle toning, but can be used to gain strength.
Tony Horton's 12-week P90X workout program primarily features high-volume and intense workouts that are designed to help you tone your muscles and decrease your body fat percentage. However, there are workouts included in the at-home program that will improve your strength and flexibility. In addition to these particular workouts, you can tweak the other workouts in the P90X program to focus more on building muscular strength.
Yoga X Workout
The Yoga X workout is scheduled at least once every week throughout the 12-week P90X program. The workout requires you to perform a variety of complex poses -- all of which elongate and stretch particular muscles -- and then hold those poses for a specific amount of time. The Runners, Crescent and Warrior poses are among those included in the workout. According to Mark D. Tran and Dr. Robert G. Holly's 2001 study published by the "Preventive Cardiology" journal, yoga effectively improves muscle flexibility. The Yoga X workout, which lasts about an hour, also increases your strength as your muscles work to hold you in position.
The X-stretch workout is also scheduled once each week. While it does incorporate a handful of yoga poses that are included in the Yoga X workout, it's significantly less intense than the yoga session. Instead of requiring you to get into and hold complex and challenging poses, flexibility is improved with static stretches -- including activities for your neck, shoulder, glutes and hamstrings -- which you hold for about 30 seconds each. According to Chat Williams of the National Strength and Conditioning Association, static stretching, when performed for 30 to 60 seconds, effectively increases flexibility. While X-stretch will improve flexibility, it's not an effective session for increasing muscular strength.
Strength Training Workouts
Strength training workouts are at the heart of P90X's program. Three strength training workouts are scheduled each week. Each one lasts about 60 minutes and focuses on two to three particular muscle groups, which allows you to complete a high number of exercises, sets and reps for each group. The program features workouts focusing on your chest and back; shoulders and arms; legs and back; chest, shoulders and triceps; and back and biceps. P90X also includes Core Synergistics and Ab Ripper X workouts, which focus on your core muscles. When you're just starting to train, these workouts will provide enough of a stimulus to help you tone your body, but are not designed for maximum strength gains. After about a month you'll need to tweak the strength workouts slightly to continue to develop.
Tweaking the P90X Program for Strength
Because P90X's strength workouts assign you a high number of reps for each exercise, the weight you'll need to use won't be adequate for maximum strength improvements. Therefore, instead of performing an exercise for 30 to 60 seconds and completing 12 to 20 reps, as the P90X training videos suggest, select a heavier weight and perform six reps of each exercise. When you're training for strength, you'll need more rest between sets, so as the lifters on the videos finish their high-rep sets, use those opportunities to allow your muscles to recover.