Three types of Pain or tapas (adhyatmik – spiritual, adhidevik – environmental and adhibhautik – physical).
Aseshatapataptanam samasrayamatho hathah /
aseshayogayuktanamadharakamatho hathah // (Chapter -1, Verse -10).
For those continually tempered by the heat of tapas or austerities (the three types of pain – spiritual, environmental and physical) Hatha Yoga is like the hermitage giving protection from the heat. (Chapter -1, Verse -10).