Traders, Bankers, coders and other office slaves sit (on chair) for long hours on daily basis. The hours and days add up and result in postural imbalances that cause other issues. Sitting cannot be avoided for most of these professionals. So, any well constructed Āsana training should address restoration (i.e. mitigate/correct the imbalance from sitting) and more importantly, preparation (i.e. prepare the body adequately for sitting prolonged time).
Sitting and Postural Imbalance
Picture the sitting position. The L shape fold at the hip leaves the hip-flexor muscle in contracted state. The hip flexors run from the lower spine (lumbar region), through the hip joints, to the femurs. When they flex (i.e. contract), legs are pulled up to the torso or the torso fold forward towards legs (or both). The chair, by offering support, deactivates the glutes. Compare this with “unassisted” sitting like squatting on the floor. The glutes stay active and engaged.
Shortened hip flexors inhibit extension of hips, so the hips tend to tip forward resulting in the familiar anterior pelvic tilt (APT). The shortened hip-flexor pulls the torso forward and down, when standing upright. If the glute muscles are not strong, this tipping leaves the hamstrings in a stretched state. This also pulls torso forward and down, when standing upright. The only way to keep an upright standing posture is then to recruit lower back muscles.
In other words, prolonged sitting leaves you with over-worked hip flexors, hamstrings and lower back muscles and under-worked glutes.
Stretching Tight Hamstrings?
The person will most likely have difficulty with standing (or sitting) forward fold. He or she will probably have to generously bend the knees for the hands to be on the floor. Frequently, this gets diagnosed as “tight hamstrings”. Many beginner Yoga classes have a lot of hamstring stretches.
However, for a person, who sits prolonged hours on a chair, hamstrings will be in a stretched state. They might be tight, but they are stretched tight. Stretching them even further will likely cause injury and more importantly, will aggravate the imbalance (the hips will be able to tilt even more forward, resulting in more load on the lower back and so on). The result is that, even if the āsana practice leaves you with a feeling of nice stretch of the back, the (inadvertent) aggravation of imbalance could lead to more lower back stress.
Note: Ashtanga Primary Series has insane number of forward folds. Given that the tradition is that you work up the series linearly, these forward folds (every fold compresses the hip flexors) could aggravate the imbalance from sitting and hence need to modified.
Any Āsana routine (be it for restoration or otherwise) must be a complete practice in itself i.e. mobilise spine in all planes of movement. Some postures may be selected and held for longer duration to address specific restorative or preparatory elements. Also, āsana practice must be done with Vinyasa for maximum benefit (see the article on Vinyasa for more information).
Restoration in this context should focus on stretching the hip flexors, releasing the hamstrings and stretching the lower back muscles. Urdhva Mukha Svānāsana or Upward facing dog (active, strong legs with glutes contracted), Veerabhadrāsana or Warrior-1 pose modification with heel of the back leg lifted to engage hamstrings and glutes (see figure 4 here) and Ustrāsana or Camel pose are some āsanas useful to stretch the hip flexors.
Preparation for sitting must focus on strength and flexibility of glutes, developing core strength and strength and flexibility of back muscles. All these must be done with as little stress on the hip flexors as possible. Typically “core strengthening” exercises tend to work the hip flexors more than the abdominal muscles (e.g. leg lifts, boat pose, etc). These need to be moderated or avoided. Utkatāsana or Chair pose, Shalabhasana or Locust pose and straight arm plank are some useful āsanas.