What is PiYo? This article from The Nest explains it very well:
PiYo is a total-body fitness system designed to whip you into shape from head to toe. It combines the practices of Pilates and yoga to help you build strength, lose weight, increase flexibility and have a great time doing it. PiYo was created by Chalene Johnson, the founder of the Turbo Kick system. It was designed for people who want the mind-body benefits of a yoga or Pilates workout, but with a higher-energy, higher-sweat class.
PiYo is different than other yoga and Pilates blends in many ways. While it does blend together these two mind-body exercises, it also adds in components of martial arts and dance for a more intense, kick-booty workout. PiYo also prides itself on using upbeat, mainstream music, rather than traditional zen yoga music, to keep students excited, interested and in the zone during the workout.
The PiYo system is a total-body strengthening workout. Poses such as plank, side plank, core work, lunges and squats are key elements to engage the large and small muscles of the body. By working in and out of these poses, you build strength using your own body's resistance. In some classes, light hand weights are also used to increase the amount of strength building. In this style of classes, your muscles are worked to be toned and sculpted, but not bulky as in some classes.
Unlike most yoga and Pilates classes, PiYo classes are aerobic. PiYo classes link together dynamic, constantly flowing exercises to increase your heart rate, burn calories and make you sweat. These classes are low-impact but high energy, with moves and poses taken from traditional yoga, Pilates and dance, linked together in a new way to add more cardio and fun. These moves include flowing in and out of Warrior pose, stepping in and out of lunges, and flowing through traditional Sun Salutations.
According to PiYo teachers, these classes not only build muscle and help you increase your cardiac health, but they also have additional benefits. The poses and moves help add flexibility to the muscles. The teachers also claim that these exercises help to increase the range of motion in your joints, improve your balance, improve energy and reduce stress, for a total mind-body, blissed-out workout.