Several schools of yoga exist and use all or some of the eight limbs.
The traditional practice of yoga was quite rigorous. A lifelong devotion to the practice and adherence to strict sacrifices was expected. Later-age yoga teachers have modified the techniques, and various paths emerged:
Bhakti yoga: the path of devotion
Gyana yoga: the path of knowledge
Raja yoga: the path of wisdom to self-realization and enlightenment
Karma yoga: the path of action
Other techniques such as hatha yoga (path of physical self-discipline), mudra yoga (the path of channeling life force), and chakra yoga (the path of energy forces) have also gained popularity.
Today, many schools of yoga have simplified the techniques and made them easy to practice for working people.
The system of yoga is in the process of developing as an organized science. Various techniques have developed and become popular throughout the world, particularly in the West, which are, in comparison with the old methods, simpler and less time consuming. Examples of popular systems in the West include kriya yoga and Simplified Kundalini Yoga.
Kriya yoga became popular in the West because of the efforts of its founder, Paramhansa Yogananda and the Self-Realization Fellowship in the United States. The word kriya is derived from the Sanskrit root kri meaning "to do," "to act," and "to react." This method involves a psychophysiological method by which human blood is decarbonated and recharged with oxygen. This extra oxygen is converted into life current to rejuvenate the central nervous system, lessen and prevent the decay of tissues, and enhance evolution of the mind.
One well-evolved school of yoga is kundalini yoga, or a system of primordial energy unification. The hallmark of this school is that it starts from the seventh step in Asthangayoga that of Dhyana or meditation.
In kundalini yoga, the fundamental meditation technique involves performing a "formless" contemplation at different points including the pituitary and the hypothalamus glands. In addition to the meditation, selected asanas, breathing techniques, and relaxation geared primarily toward muscular strain reduction, enhancing the vital capacity of the lungs, and balancing the endocrine and central nervous systems are also practiced. With this system of yoga, physical exercises are simplified.
The techniques of this school have been popularized by the Universal Peace Sanctuary (Erode, India) established in 1937 and World Community Service Centre (Chennai, India) established in 1958. Both these organizations have several branches all over the world and have taught several thousands of practitioners in these techniques.
A recent variation is called power yoga, in which practitioners take a more athletic approach and move rapidly from one pose to another.