Power yoga is a form of Vinyasa yoga in a heated room.
Vinyasa Yoga is characterized by a focus on viṅyāsa, or a dynamic connecting posture, that creates a flow between the more static traditional yoga postures. Vinyasa translates as linking and the system also implies the linking of the movement to the breath. Essentially the breath dictates the movement and the length of time held in the postures. Unlike some Hatha yoga styles, attention is also placed on the journey between the postures not just the postures themselves. The viṅyāsa 'flow' is a variant of Sūrya namaskāra, the Sun Salutation. The whole practice is defined by six specific series of postures, always done in the same order, combined with specific breathing patterns (Free breathing with the ujjāyī sound).
A standard viṅyāsa consists (for example) of the flow from caturaṅga, or plank, to caturaṅga daṇḍāsana, or low plank, to ūrdhva mukha śvānāsana or upward-facing dog, to Adho Mukha Svanasana, or downward-facing dog. The purpose of viṅyāsa is to create heat in the body, which leads to purification of the body through increased circulation and sweating. Ashtanga Vinyasa brings in the principles of Agni and inversion to purify the entire body.
It also improves flexibility, as well as tendon and hard tissue strength, allowing the student to practice advanced āsanas with reduced risk of injury.