Extension, in compare with asana movement.

Extension is an increase in the angle of a joint. Extension of a joint makes a body part move in a backwards direction. (The knee joint is the only exception to this rule where flexion moves the lower leg backwards and extension moves the lower leg forwards.). Spinal extension is a movement that lengthens the spine upwards (axial extension) and backwards. Otherwise known as backward bends (or simply backbends) in yoga, spinal extension stretches and strengthens the spine, particularly opening up the thoracic spine and the muscles of the chest and shoulders.