About the props
BKS Iyengar has introduced numerous innovative accessories, called "props"in English, like walls, straps, blankets, chairs, bolsters, ropes, sundries such as wooden bricks, benches, quarter-rounds, back-bend supports, tressler, etc.
An article published in Yoga Rahasya (Vol. 12, No. 5, 2005), explains the usefulness of these materials. Here are some excerpts:
Yoga, a neurological science
In the beginning of my teaching, I asked myself how I could attract people to yoga. I wanted to transmit the experience of extension and relaxation which go together. For this reason I introduced the props and this made yoga
Relaxing alone or independently is not easy. With the props, relaxation becomes possible. If you do Viparita Dandasana on a chair, the brain relaxes.
Uttitha Trikonasana on the tressler allows you to feel less exhausted.
Sirsasana on ropes brings biological relaxation while Sirsasana on the floor brings a psychological demand. Biological relaxation gives neurological strength.
Viparita Dandasana on a chair offers a certain comfort. The props act like a balancer which brings neurological control.
Neurological body is the medium between psychology and organic body. That's why you have to work on neurology. Yoga is completely a neurological
science. Neurology is the hub of the life force. In each asana, you are working on muscles and bones.
Everything begins with fluids in joints. If you move the fluids, blood circulates. Without lubrication of the joints there is arthritis and blood does not circulate. When blood circulates, muscles develop and tone the inner and outer body. Inner body is about bone marrow. It's imperative that muscles move towards the bones so the bones generate new blood.This is the mystery of yoga. That's why you need to study the depth of the asanas.