Hatha Yoga describes the Shatkarma in the second chapter of the Hatha Yoga Pradipika. Shat is Sanskrit for 6 and Karma is the word for Action. The ancient Yogis believed that in order to understand the universe you needed to first clear out the impurities, toxins and distractions of humanity. To do so you had to begin by cleaning out your body.
The Encyclopaedia of Traditional Asanas describes hundreds of seats; various ways in which to move the body in an effort to eliminate the limitations that result in discomfort. The Sanskrit word "as" means "to sit." Asana can also be interpreted as "establishment in the original state." The postures were designed to create heat (Tapas) allowing us to eliminate toxins and impurities in the physical body so that we could move into svabhava (introversion). The practice of Asana eventually provides us with steadiness and inner awareness of our True Self.
Breath and movement are the keys to Yoga. Every breath directs and deepens movement. Directed breath or kripalu.org/resources/why-do-pranayama Pranayama specifically directs your body, mind and internal energy. Proper practice of Pranayama can lead to the creation of body heat, spiritual experiences and energetic shifts. The formal practices described by Hatha Yoga are done so with a specific intended use and course.
By today's standards some of the practices described by Hatha Yoga are downright disgusting. Swallowing a milk soaked rag (Dhuati Karma) doesn't sound like something I want to do. However, there are many practices that we continue to apply today in order to keep our bodies clean.
Neti: Nasal cleaning involved the use of a string threaded up the nostrils and through the sinus passage. Today we use neti pots, sprays and tissues.
Dhauti: Cleansing of the digestive tract included milk soaked rags and forced vomitting. Modern science has helped us to identify foods that can clean our system.
Bhasti: Thank goodness for modern science and doctors who help us to keep our colons healthy.
Trataka: Blinkless gazing was used to clean the eyes. Many of us practice this just because the view is so beautiful. Eye drops assist us when we are ill or require a little help on a dry day.
Consider that which you do to keep your body healthy and clean. Many of our current practices and habits have roots in those of the ancient Yogis. What practices can you add to you life to clear away the toxins from the world around you, eliminate that which you do not need and create a bit more space for internal focus?