Standing poses, also known as Utthita Sthiti in Sanskrit, are considered the foundation of Iyengar Yoga curriculum. When a student first learns yoga poses in the Iyengar way, s/he begins with standing poses such as Triangle pose, Warrior poses and perhaps the balancing Tree pose as well. In essence, standing poses tone the legs and back muscles and prepare the student for other poses that deal with forward-bending or back-bending movements.
In standing poses, the student begins to discover the close connections how the feet and legs align with other parts of the body. For example, in Triangle pose, if the front (the moving side) foot is not centered or the front leg is not fully extended, that side of the chest will not be able to fully open. When the front leg is fully extended, observe the parallel alignment of the sides of the chest.
Moreover, in standing poses, the student learns how to engage the gravity by working on muscular contractions, extension, abduction, adduction and rotation. Revolving Triangle pose, for example, helps the student to develop a sense of balance by contracting the outer musculature toward the core, thus allowing the spinal muscles and the chest muscles to rotate.
Furthermore, standing poses energize and build stamina. In Warrior I pose, the student brings the arms up overhead, the body and the energy center are immediately charged upwards.
Below is a sample video in which a senior Iyengar Yoga teacher John Schumacher instructs on Triangle Pose. Pay special attention to the details on the alignment of the feet and the actions of the legs. See how the workings of the feet and legs allow the extension of the spine and expansion of the chest.