There are many interpretations, styles and forms of Hatha Yoga. The Sanskrit word Hatha actually means forceful! Which is strange because Hatha Yoga in the west can sometimes mean easy, gentle, restorative. Back around the 11th century a powerful Yogi named Goraksha created a system of Yoga, quite different than the traditionalist called Hatha Yoga. His philosophy was to use the body as a means to reach Samadhi, (enlightenment). To forcefully open the physical and ethereal channels, (Nadis), which will allow the subtle energies, (Prana & Shakti), to free flow in, through and around us! The Barkan Method of Hot Yoga interprets and embraces Goraksha’s teaching!!
Before Goraksha, practicing asana was primarily done to prepare the yogi for meditation. Goraksha was born in Bengal and was said to be a native of Punjab, located in the northeast of India. My theory is that over the last thousand years the various regions of India interpreted the teachings of Goraksha in a multitude of ways, hence the different styles of Hatha Yoga; Iyengar, Ashtanga, Vinyasa, Bikram and of course the Barkan Method of Hot Yoga.