One thing that makes a good yoga flow is the use of counter poses. These poses are the ones that ‘reset’ the body. Every pose has one that follows it which will allow the spine to reset itself. These poses are particularly important following poses that challenge the student in ways that their body is not use to. For example, after doing a cow pose it is often then switched to a cat pose, or after the spine is put into extension it is moved into flexion. Many times this will then be followed by a twist, to neutralize the spine all together.
Counter poses show fluidly in a flow, allowing a beautiful dance to begin in an āsana practice. For example, say a yogi starts out their practice with an excessive number of sun salutations—arms over head, forward fold, flatten back, top of a pushup, lower down, cobra, downward dog, back to forward fold, flatten back, back to mountain pose—after a number of these there is an excessive amount of pressure placed on the wrists. In an Ashtanga flow, Sri K. Pattabhi Jois would recommend Padangushthasana and Pada Hastasana. Both of these poses take the weight out of the wrists and allowed them to rest for a time before beginning the rest of the Primary Series. Still even after doing a counter pose, there are counter poses to that pose. This action and reaction would build up the flow for the student to allow the dance to begin.
This is much the concept the T.K.V. Desikachar teaches in his book The Heart of Yoga, Developing a Personal Practice. Another example of poses and counter poses creating a beautiful flow is shown in his book, starting with Shirshasana or head stand—granted a student would never start a flow with Shirshasana without first being warmed up, generally this poses is put towards the end of any practice. Desikachar suggests that a student after practicing Shirshasana would then move into Halasana (plow pose) to Salamba (shoulder stand) to Halasana again finally come into Matsyasana (fish pose). Desikachar says that given the amount of stress placed on the neck during Shirshasana, Salamba is the perfect counter pose because it elongates the neck. First it is always wise to come into Halasana before Salamba, because it prepares the body. Finally a student must counter the amount of stress in the upper body created by Salamba, thus moving into Matsyasana. Many yogis would then recommend that a student practice some kind of twist, usually a reclined twist, to neutralize the spine. Just this one sequence can be a focus of an entire practice. If so it would create its own flow upon its self, with different poses warming and preparing the body for Shirshasana, and their counter poses opening up to the student into a seamless dance.
Of course there is nothing in yoga that is reserved purely to the mat. Counter poses allow one to flow in their practice teaching balance both on and off the mat. The idea that is mostly accepted is that to every action there are equal and opposite reactions. Both Desikachar and Paramahansa Yogananda agree that to every action there are positive and negative reactions. Counter poses allow a student to feel in the middle space and find balance in their practice on their mats. Yet off the mat students begin to see how everything that they do has these reactions and many begin to see different ways in which they can counter the actions and minimize the negative reactions. Naturally a yoga practice opens up a student to the world around them and a better way of living.
Again counter poses are one of the fundamental ideas behind a balanced yoga practice. It allows not only a physical practice to flow and flourish, but it also teaches valuable lesions off the mat, showing the reactions to many of our actions. With this teaching it brings awareness to our bodies, minds, emotions, and spirits.